Merge remote-tracking branch 'upstream/master'

algorithms/README.md

@@ -16,3 +16,4 @@
 - [Introduction to Minimax Algorithm](http://www.baeldung.com/java-minimax-algorithm)
 - [How to Calculate Levenshtein Distance in Java?](http://www.baeldung.com/java-levenshtein-distance)
 - [How to Find the Kth Largest Element in Java](http://www.baeldung.com/java-kth-largest-element)
+- [Multi-Swarm Optimization Algorithm in Java](http://www.baeldung.com/java-multi-swarm-algorithm)

algorithms/pom.xml

@@ -9,6 +9,7 @@
         <exec-maven-plugin.version>1.5.0</exec-maven-plugin.version>
         <lombok.version>1.16.12</lombok.version>
         <commons-math3.version>3.6.1</commons-math3.version>
+        <tradukisto.version>1.0.1</tradukisto.version>
     </properties>
 
     <parent>
@@ -39,6 +40,11 @@
             <artifactId>jgrapht-core</artifactId>
             <version>1.0.1</version>
         </dependency>
+        <dependency>
+            <groupId>pl.allegro.finance</groupId>
+            <artifactId>tradukisto</artifactId>
+            <version>${tradukisto.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.assertj</groupId>
             <artifactId>assertj-core</artifactId>
@@ -46,7 +52,6 @@
             <scope>test</scope>
         </dependency>
     </dependencies>
-
     <build>
         <pluginManagement>
             <plugins>

algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Constants.java

@@ -0,0 +1,47 @@
+package com.baeldung.algorithms.multiswarm;
+
+/**
+ * Constants used by the Multi-swarm optimization algorithms.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class Constants {
+
+	/**
+	 * The inertia factor encourages a particle to continue moving in its
+	 * current direction.
+	 */
+	public static final double INERTIA_FACTOR = 0.729;
+
+	/**
+	 * The cognitive weight encourages a particle to move toward its historical
+	 * best-known position.
+	 */
+	public static final double COGNITIVE_WEIGHT = 1.49445;
+
+	/**
+	 * The social weight encourages a particle to move toward the best-known
+	 * position found by any of the particle’s swarm-mates.
+	 */
+	public static final double SOCIAL_WEIGHT = 1.49445;
+
+	/**
+	 * The global weight encourages a particle to move toward the best-known
+	 * position found by any particle in any swarm.
+	 */
+	public static final double GLOBAL_WEIGHT = 0.3645;
+
+	/**
+	 * Upper bound for the random generation. We use it to reduce the
+	 * computation time since we can rawly estimate it.
+	 */
+	public static final int PARTICLE_UPPER_BOUND = 10000000;
+
+	/**
+	 * Private constructor for utility class.
+	 */
+	private Constants() {
+	}
+
+}

algorithms/src/main/java/com/baeldung/algorithms/multiswarm/FitnessFunction.java

@@ -0,0 +1,21 @@
+package com.baeldung.algorithms.multiswarm;
+
+/**
+ * Interface for a fitness function, used to decouple the main algorithm logic
+ * from the specific problem solution.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public interface FitnessFunction {
+
+	/**
+	 * Returns the fitness of a particle given its position.
+	 * 
+	 * @param particlePosition
+	 *            the position of the particle
+	 * @return the fitness of the particle
+	 */
+	public double getFitness(long[] particlePosition);
+
+}

algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Multiswarm.java

@@ -0,0 +1,227 @@
+package com.baeldung.algorithms.multiswarm;
+
+import java.util.Arrays;
+import java.util.Random;
+
+/**
+ * Represents a collection of {@link Swarm}.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class Multiswarm {
+
+	/**
+	 * The swarms managed by this multiswarm.
+	 */
+	private Swarm[] swarms;
+
+	/**
+	 * The best position found within all the {@link #swarms}.
+	 */
+	private long[] bestPosition;
+
+	/**
+	 * The best fitness score found within all the {@link #swarms}.
+	 */
+	private double bestFitness = Double.NEGATIVE_INFINITY;
+
+	/**
+	 * A random generator.
+	 */
+	private Random random = new Random();
+
+	/**
+	 * The fitness function used to determine how good is a particle.
+	 */
+	private FitnessFunction fitnessFunction;
+
+	/**
+	 * Instantiates a new Multiswarm.
+	 * 
+	 * @param numSwarms
+	 *            the number of {@link #swarms}
+	 * @param particlesPerSwarm
+	 *            the number of particle for each {@link #swarms}
+	 * @param fitnessFunction
+	 *            the {@link #fitnessFunction}
+	 */
+	public Multiswarm(int numSwarms, int particlesPerSwarm, FitnessFunction fitnessFunction) {
+		this.fitnessFunction = fitnessFunction;
+		this.swarms = new Swarm[numSwarms];
+		for (int i = 0; i < numSwarms; i++) {
+			swarms[i] = new Swarm(particlesPerSwarm);
+		}
+	}
+
+	/**
+	 * Main loop of the algorithm. Iterates all particles of all
+	 * {@link #swarms}. For each particle, computes the new fitness and checks
+	 * if a new best position has been found among itself, the swarm and all the
+	 * swarms and finally updates the particle position and speed.
+	 */
+	public void mainLoop() {
+		for (Swarm swarm : swarms) {
+			for (Particle particle : swarm.getParticles()) {
+
+				long[] particleOldPosition = particle.getPosition().clone();
+
+				// Calculate the particle fitness.
+				particle.setFitness(fitnessFunction.getFitness(particleOldPosition));
+
+				// Check if a new best position has been found for the particle
+				// itself, within the swarm and the multiswarm.
+				if (particle.getFitness() > particle.getBestFitness()) {
+					particle.setBestFitness(particle.getFitness());
+					particle.setBestPosition(particleOldPosition);
+
+					if (particle.getFitness() > swarm.getBestFitness()) {
+						swarm.setBestFitness(particle.getFitness());
+						swarm.setBestPosition(particleOldPosition);
+
+						if (swarm.getBestFitness() > bestFitness) {
+							bestFitness = swarm.getBestFitness();
+							bestPosition = swarm.getBestPosition().clone();
+						}
+
+					}
+				}
+
+				// Updates the particle position by adding the speed to the
+				// actual position.
+				long[] position = particle.getPosition();
+				long[] speed = particle.getSpeed();
+
+				position[0] += speed[0];
+				position[1] += speed[1];
+
+				// Updates the particle speed.
+				speed[0] = getNewParticleSpeedForIndex(particle, swarm, 0);
+				speed[1] = getNewParticleSpeedForIndex(particle, swarm, 1);
+			}
+		}
+	}
+
+	/**
+	 * Computes a new speed for a given particle of a given swarm on a given
+	 * axis. The new speed is computed using the formula:
+	 * 
+	 * <pre>
+	 * ({@link Constants#INERTIA_FACTOR} * {@link Particle#getSpeed()}) + 
+	 * (({@link Constants#COGNITIVE_WEIGHT} * random(0,1)) * ({@link Particle#getBestPosition()} - {@link Particle#getPosition()})) +
+	 * (({@link Constants#SOCIAL_WEIGHT} * random(0,1)) * ({@link Swarm#getBestPosition()} - {@link Particle#getPosition()})) + 
+	 * (({@link Constants#GLOBAL_WEIGHT} * random(0,1)) * ({@link #bestPosition} - {@link Particle#getPosition()}))
+	 * </pre>
+	 *
+	 * @param particle
+	 *            the particle whose new speed needs to be computed
+	 * @param swarm
+	 *            the swarm which contains the particle
+	 * @param index
+	 *            the index of the particle axis whose speeds needs to be
+	 *            computed
+	 * @return the new speed of the particle passed on the given axis
+	 */
+	private int getNewParticleSpeedForIndex(Particle particle, Swarm swarm, int index) {
+		return (int) ((Constants.INERTIA_FACTOR * particle.getSpeed()[index])
+				+ (randomizePercentage(Constants.COGNITIVE_WEIGHT)
+						* (particle.getBestPosition()[index] - particle.getPosition()[index]))
+				+ (randomizePercentage(Constants.SOCIAL_WEIGHT)
+						* (swarm.getBestPosition()[index] - particle.getPosition()[index]))
+				+ (randomizePercentage(Constants.GLOBAL_WEIGHT)
+						* (bestPosition[index] - particle.getPosition()[index])));
+	}
+
+	/**
+	 * Returns a random number between 0 and the value passed as argument.
+	 *
+	 * @param value
+	 *            the value to randomize
+	 * @return a random value between 0 and the one passed as argument
+	 */
+	private double randomizePercentage(double value) {
+		return random.nextDouble() * value;
+	}
+
+	/**
+	 * Gets the {@link #bestPosition}.
+	 *
+	 * @return the {@link #bestPosition}
+	 */
+	public long[] getBestPosition() {
+		return bestPosition;
+	}
+
+	/**
+	 * Gets the {@link #bestFitness}.
+	 *
+	 * @return the {@link #bestFitness}
+	 */
+	public double getBestFitness() {
+		return bestFitness;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#hashCode()
+	 */
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		long temp;
+		temp = Double.doubleToLongBits(bestFitness);
+		result = prime * result + (int) (temp ^ (temp >>> 32));
+		result = prime * result + Arrays.hashCode(bestPosition);
+		result = prime * result + ((fitnessFunction == null) ? 0 : fitnessFunction.hashCode());
+		result = prime * result + ((random == null) ? 0 : random.hashCode());
+		result = prime * result + Arrays.hashCode(swarms);
+		return result;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#equals(java.lang.Object)
+	 */
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		Multiswarm other = (Multiswarm) obj;
+		if (Double.doubleToLongBits(bestFitness) != Double.doubleToLongBits(other.bestFitness))
+			return false;
+		if (!Arrays.equals(bestPosition, other.bestPosition))
+			return false;
+		if (fitnessFunction == null) {
+			if (other.fitnessFunction != null)
+				return false;
+		} else if (!fitnessFunction.equals(other.fitnessFunction))
+			return false;
+		if (random == null) {
+			if (other.random != null)
+				return false;
+		} else if (!random.equals(other.random))
+			return false;
+		if (!Arrays.equals(swarms, other.swarms))
+			return false;
+		return true;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#toString()
+	 */
+	@Override
+	public String toString() {
+		return "Multiswarm [swarms=" + Arrays.toString(swarms) + ", bestPosition=" + Arrays.toString(bestPosition)
+				+ ", bestFitness=" + bestFitness + ", random=" + random + ", fitnessFunction=" + fitnessFunction + "]";
+	}
+
+}

algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Particle.java

@@ -0,0 +1,204 @@
+package com.baeldung.algorithms.multiswarm;
+
+import java.util.Arrays;
+
+/**
+ * Represents a particle, the basic component of a {@link Swarm}.
+ * 
+ * @author Donato Rimenti
+ * 
+ */
+public class Particle {
+
+	/**
+	 * The current position of this particle.
+	 */
+	private long[] position;
+
+	/**
+	 * The speed of this particle.
+	 */
+	private long[] speed;
+
+	/**
+	 * The fitness of this particle for the current position.
+	 */
+	private double fitness;
+
+	/**
+	 * The best position found by this particle.
+	 */
+	private long[] bestPosition;
+
+	/**
+	 * The best fitness found by this particle.
+	 */
+	private double bestFitness = Double.NEGATIVE_INFINITY;
+
+	/**
+	 * Instantiates a new Particle.
+	 *
+	 * @param initialPosition
+	 *            the initial {@link #position}
+	 * @param initialSpeed
+	 *            the initial {@link #speed}
+	 */
+	public Particle(long[] initialPosition, long[] initialSpeed) {
+		this.position = initialPosition;
+		this.speed = initialSpeed;
+	}
+
+	/**
+	 * Gets the {@link #position}.
+	 *
+	 * @return the {@link #position}
+	 */
+	public long[] getPosition() {
+		return position;
+	}
+
+	/**
+	 * Gets the {@link #speed}.
+	 *
+	 * @return the {@link #speed}
+	 */
+	public long[] getSpeed() {
+		return speed;
+	}
+
+	/**
+	 * Gets the {@link #fitness}.
+	 *
+	 * @return the {@link #fitness}
+	 */
+	public double getFitness() {
+		return fitness;
+	}
+
+	/**
+	 * Gets the {@link #bestPosition}.
+	 *
+	 * @return the {@link #bestPosition}
+	 */
+	public long[] getBestPosition() {
+		return bestPosition;
+	}
+
+	/**
+	 * Gets the {@link #bestFitness}.
+	 *
+	 * @return the {@link #bestFitness}
+	 */
+	public double getBestFitness() {
+		return bestFitness;
+	}
+
+	/**
+	 * Sets the {@link #position}.
+	 *
+	 * @param position
+	 *            the new {@link #position}
+	 */
+	public void setPosition(long[] position) {
+		this.position = position;
+	}
+
+	/**
+	 * Sets the {@link #speed}.
+	 *
+	 * @param speed
+	 *            the new {@link #speed}
+	 */
+	public void setSpeed(long[] speed) {
+		this.speed = speed;
+	}
+
+	/**
+	 * Sets the {@link #fitness}.
+	 *
+	 * @param fitness
+	 *            the new {@link #fitness}
+	 */
+	public void setFitness(double fitness) {
+		this.fitness = fitness;
+	}
+
+	/**
+	 * Sets the {@link #bestPosition}.
+	 *
+	 * @param bestPosition
+	 *            the new {@link #bestPosition}
+	 */
+	public void setBestPosition(long[] bestPosition) {
+		this.bestPosition = bestPosition;
+	}
+
+	/**
+	 * Sets the {@link #bestFitness}.
+	 *
+	 * @param bestFitness
+	 *            the new {@link #bestFitness}
+	 */
+	public void setBestFitness(double bestFitness) {
+		this.bestFitness = bestFitness;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#hashCode()
+	 */
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		long temp;
+		temp = Double.doubleToLongBits(bestFitness);
+		result = prime * result + (int) (temp ^ (temp >>> 32));
+		result = prime * result + Arrays.hashCode(bestPosition);
+		temp = Double.doubleToLongBits(fitness);
+		result = prime * result + (int) (temp ^ (temp >>> 32));
+		result = prime * result + Arrays.hashCode(position);
+		result = prime * result + Arrays.hashCode(speed);
+		return result;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#equals(java.lang.Object)
+	 */
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		Particle other = (Particle) obj;
+		if (Double.doubleToLongBits(bestFitness) != Double.doubleToLongBits(other.bestFitness))
+			return false;
+		if (!Arrays.equals(bestPosition, other.bestPosition))
+			return false;
+		if (Double.doubleToLongBits(fitness) != Double.doubleToLongBits(other.fitness))
+			return false;
+		if (!Arrays.equals(position, other.position))
+			return false;
+		if (!Arrays.equals(speed, other.speed))
+			return false;
+		return true;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#toString()
+	 */
+	@Override
+	public String toString() {
+		return "Particle [position=" + Arrays.toString(position) + ", speed=" + Arrays.toString(speed) + ", fitness="
+				+ fitness + ", bestPosition=" + Arrays.toString(bestPosition) + ", bestFitness=" + bestFitness + "]";
+	}
+
+}

algorithms/src/main/java/com/baeldung/algorithms/multiswarm/Swarm.java

@@ -0,0 +1,155 @@
+package com.baeldung.algorithms.multiswarm;
+
+import java.util.Arrays;
+import java.util.Random;
+
+/**
+ * Represents a collection of {@link Particle}.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class Swarm {
+
+	/**
+	 * The particles of this swarm.
+	 */
+	private Particle[] particles;
+
+	/**
+	 * The best position found within the particles of this swarm.
+	 */
+	private long[] bestPosition;
+
+	/**
+	 * The best fitness score found within the particles of this swarm.
+	 */
+	private double bestFitness = Double.NEGATIVE_INFINITY;
+
+	/**
+	 * A random generator.
+	 */
+	private Random random = new Random();
+
+	/**
+	 * Instantiates a new Swarm.
+	 *
+	 * @param numParticles
+	 *            the number of particles of the swarm
+	 */
+	public Swarm(int numParticles) {
+		particles = new Particle[numParticles];
+		for (int i = 0; i < numParticles; i++) {
+			long[] initialParticlePosition = { random.nextInt(Constants.PARTICLE_UPPER_BOUND),
+					random.nextInt(Constants.PARTICLE_UPPER_BOUND) };
+			long[] initialParticleSpeed = { random.nextInt(Constants.PARTICLE_UPPER_BOUND),
+					random.nextInt(Constants.PARTICLE_UPPER_BOUND) };
+			particles[i] = new Particle(initialParticlePosition, initialParticleSpeed);
+		}
+	}
+
+	/**
+	 * Gets the {@link #particles}.
+	 *
+	 * @return the {@link #particles}
+	 */
+	public Particle[] getParticles() {
+		return particles;
+	}
+
+	/**
+	 * Gets the {@link #bestPosition}.
+	 *
+	 * @return the {@link #bestPosition}
+	 */
+	public long[] getBestPosition() {
+		return bestPosition;
+	}
+
+	/**
+	 * Gets the {@link #bestFitness}.
+	 *
+	 * @return the {@link #bestFitness}
+	 */
+	public double getBestFitness() {
+		return bestFitness;
+	}
+
+	/**
+	 * Sets the {@link #bestPosition}.
+	 *
+	 * @param bestPosition
+	 *            the new {@link #bestPosition}
+	 */
+	public void setBestPosition(long[] bestPosition) {
+		this.bestPosition = bestPosition;
+	}
+
+	/**
+	 * Sets the {@link #bestFitness}.
+	 *
+	 * @param bestFitness
+	 *            the new {@link #bestFitness}
+	 */
+	public void setBestFitness(double bestFitness) {
+		this.bestFitness = bestFitness;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#hashCode()
+	 */
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		long temp;
+		temp = Double.doubleToLongBits(bestFitness);
+		result = prime * result + (int) (temp ^ (temp >>> 32));
+		result = prime * result + Arrays.hashCode(bestPosition);
+		result = prime * result + Arrays.hashCode(particles);
+		result = prime * result + ((random == null) ? 0 : random.hashCode());
+		return result;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#equals(java.lang.Object)
+	 */
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		Swarm other = (Swarm) obj;
+		if (Double.doubleToLongBits(bestFitness) != Double.doubleToLongBits(other.bestFitness))
+			return false;
+		if (!Arrays.equals(bestPosition, other.bestPosition))
+			return false;
+		if (!Arrays.equals(particles, other.particles))
+			return false;
+		if (random == null) {
+			if (other.random != null)
+				return false;
+		} else if (!random.equals(other.random))
+			return false;
+		return true;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see java.lang.Object#toString()
+	 */
+	@Override
+	public String toString() {
+		return "Swarm [particles=" + Arrays.toString(particles) + ", bestPosition=" + Arrays.toString(bestPosition)
+				+ ", bestFitness=" + bestFitness + ", random=" + random + "]";
+	}
+
+}

algorithms/src/main/java/com/baeldung/algorithms/numberwordconverter/NumberWordConverter.java

@@ -0,0 +1,75 @@
+package com.baeldung.algorithms.numberwordconverter;
+
+import java.math.BigDecimal;
+
+import pl.allegro.finance.tradukisto.MoneyConverters;
+
+public class NumberWordConverter {
+
+    public static final String INVALID_INPUT_GIVEN = "Invalid input given";
+
+    public static final String[] ones = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" };
+
+    public static final String[] tens = {
+      "", // 0
+      "", // 1
+      "twenty", // 2
+      "thirty", // 3
+      "forty", // 4
+      "fifty", // 5
+      "sixty", // 6
+      "seventy", // 7
+      "eighty", // 8
+      "ninety" // 9
+    };
+
+    public static String getMoneyIntoWords(String input) {
+        MoneyConverters converter = MoneyConverters.ENGLISH_BANKING_MONEY_VALUE;
+        return converter.asWords(new BigDecimal(input));
+    }
+
+    public static String getMoneyIntoWords(final double money) {
+        long dollar = (long) money;
+        long cents = Math.round((money - dollar) * 100);
+        if (money == 0D) {
+            return "";
+        }
+        if (money < 0) {
+            return INVALID_INPUT_GIVEN;
+        }
+        String dollarPart = "";
+        if (dollar > 0) {
+            dollarPart = convert(dollar) + " dollar" + (dollar == 1 ? "" : "s");
+        }
+        String centsPart = "";
+        if (cents > 0) {
+            if (dollarPart.length() > 0) {
+                centsPart = " and ";
+            }
+            centsPart += convert(cents) + " cent" + (cents == 1 ? "" : "s");
+        }
+        return dollarPart + centsPart;
+    }
+
+    private static String convert(final long n) {
+        if (n < 0) {
+            return INVALID_INPUT_GIVEN;
+        }
+        if (n < 20) {
+            return ones[(int) n];
+        }
+        if (n < 100) {
+            return tens[(int) n / 10] + ((n % 10 != 0) ? " " : "") + ones[(int) n % 10];
+        }
+        if (n < 1000) {
+            return ones[(int) n / 100] + " hundred" + ((n % 100 != 0) ? " " : "") + convert(n % 100);
+        }
+        if (n < 1_000_000) {
+            return convert(n / 1000) + " thousand" + ((n % 1000 != 0) ? " " : "") + convert(n % 1000);
+        }
+        if (n < 1_000_000_000) {
+            return convert(n / 1_000_000) + " million" + ((n % 1_000_000 != 0) ? " " : "") + convert(n % 1_000_000);
+        }
+        return convert(n / 1_000_000_000) + " billion" + ((n % 1_000_000_000 != 0) ? " " : "") + convert(n % 1_000_000_000);
+    }
+}

algorithms/src/main/java/com/baeldung/algorithms/sudoku/BacktrackingAlgorithm.java

@@ -40,15 +40,15 @@ public class BacktrackingAlgorithm {
     }
 
     private boolean solve(int[][] board) {
-        for (int r = BOARD_START_INDEX; r < BOARD_SIZE; r++) {
+        for (int row = BOARD_START_INDEX; row < BOARD_SIZE; row++) {
-            for (int c = BOARD_START_INDEX; c < BOARD_SIZE; c++) {
+            for (int column = BOARD_START_INDEX; column < BOARD_SIZE; column++) {
-                if (board[r][c] == NO_VALUE) {
+                if (board[row][column] == NO_VALUE) {
                     for (int k = MIN_VALUE; k <= MAX_VALUE; k++) {
-                        board[r][c] = k;
+                        board[row][column] = k;
-                        if (isValid(board, r, c) && solve(board)) {
+                        if (isValid(board, row, column) && solve(board)) {
                             return true;
                         }
-                        board[r][c] = NO_VALUE;
+                        board[row][column] = NO_VALUE;
                     }
                     return false;
                 }
@@ -57,44 +57,44 @@ public class BacktrackingAlgorithm {
         return true;
     }
 
-    private boolean isValid(int[][] board, int r, int c) {
+    private boolean isValid(int[][] board, int row, int column) {
-        return rowConstraint(board, r) &&
+        return rowConstraint(board, row) &&
-          columnConstraint(board, c) &&
+          columnConstraint(board, column) &&
-          subsectionConstraint(board, r, c);
+          subsectionConstraint(board, row, column);
     }
 
-    private boolean subsectionConstraint(int[][] board, int r, int c) {
+    private boolean subsectionConstraint(int[][] board, int row, int column) {
         boolean[] constraint = new boolean[BOARD_SIZE];
-        int subsectionRowStart = (r / SUBSECTION_SIZE) * SUBSECTION_SIZE;
+        int subsectionRowStart = (row / SUBSECTION_SIZE) * SUBSECTION_SIZE;
         int subsectionRowEnd = subsectionRowStart + SUBSECTION_SIZE;
 
-        int subsectionColumnStart = (c / SUBSECTION_SIZE) * SUBSECTION_SIZE;
+        int subsectionColumnStart = (column / SUBSECTION_SIZE) * SUBSECTION_SIZE;
         int subsectionColumnEnd = subsectionColumnStart + SUBSECTION_SIZE;
 
-        for (int i = subsectionRowStart; i < subsectionRowEnd; i++) {
+        for (int r = subsectionRowStart; r < subsectionRowEnd; r++) {
-            for (int j = subsectionColumnStart; j < subsectionColumnEnd; j++) {
+            for (int c = subsectionColumnStart; c < subsectionColumnEnd; c++) {
-                if (!checkConstraint(board, i, constraint, j)) return false;
+                if (!checkConstraint(board, r, constraint, c)) return false;
             }
         }
         return true;
     }
 
-    private boolean columnConstraint(int[][] board, int c) {
+    private boolean columnConstraint(int[][] board, int column) {
         boolean[] constraint = new boolean[BOARD_SIZE];
         return IntStream.range(BOARD_START_INDEX, BOARD_SIZE)
-          .allMatch(i -> checkConstraint(board, i, constraint, c));
+          .allMatch(row -> checkConstraint(board, row, constraint, column));
     }
 
-    private boolean rowConstraint(int[][] board, int r) {
+    private boolean rowConstraint(int[][] board, int row) {
         boolean[] constraint = new boolean[BOARD_SIZE];
         return IntStream.range(BOARD_START_INDEX, BOARD_SIZE)
-          .allMatch(i -> checkConstraint(board, r, constraint, i));
+          .allMatch(column -> checkConstraint(board, row, constraint, column));
     }
 
-    private boolean checkConstraint(int[][] board, int r, boolean[] constraint, int c) {
+    private boolean checkConstraint(int[][] board, int row, boolean[] constraint, int column) {
-        if (board[r][c] != NO_VALUE) {
+        if (board[row][column] != NO_VALUE) {
-            if (!constraint[board[r][c] - 1]) {
+            if (!constraint[board[row][column] - 1]) {
-                constraint[board[r][c] - 1] = true;
+                constraint[board[row][column] - 1] = true;
             } else {
                 return false;
             }

algorithms/src/main/java/com/baeldung/algorithms/sudoku/DancingLinksAlgorithm.java

@@ -34,8 +34,8 @@ public class DancingLinksAlgorithm {
         dlx.runSolver();
     }
 
-    private int getIndex(int row, int col, int num) {
+    private int getIndex(int row, int column, int num) {
-        return (row - 1) * BOARD_SIZE * BOARD_SIZE + (col - 1) * BOARD_SIZE + (num - 1);
+        return (row - 1) * BOARD_SIZE * BOARD_SIZE + (column - 1) * BOARD_SIZE + (num - 1);
     }
 
     private boolean[][] createExactCoverBoard() {
@@ -51,12 +51,12 @@ public class DancingLinksAlgorithm {
     }
 
     private int checkSubsectionConstraint(boolean[][] coverBoard, int hBase) {
-        for (int br = COVER_START_INDEX; br <= BOARD_SIZE; br += SUBSECTION_SIZE) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row += SUBSECTION_SIZE) {
-            for (int bc = COVER_START_INDEX; bc <= BOARD_SIZE; bc += SUBSECTION_SIZE) {
+            for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column += SUBSECTION_SIZE) {
                 for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++, hBase++) {
-                    for (int rDelta = 0; rDelta < SUBSECTION_SIZE; rDelta++) {
+                    for (int rowDelta = 0; rowDelta < SUBSECTION_SIZE; rowDelta++) {
-                        for (int cDelta = 0; cDelta < SUBSECTION_SIZE; cDelta++) {
+                        for (int columnDelta = 0; columnDelta < SUBSECTION_SIZE; columnDelta++) {
-                            int index = getIndex(br + rDelta, bc + cDelta, n);
+                            int index = getIndex(row + rowDelta, column + columnDelta, n);
                             coverBoard[index][hBase] = true;
                         }
                     }
@@ -67,10 +67,10 @@ public class DancingLinksAlgorithm {
     }
 
     private int checkColumnConstraint(boolean[][] coverBoard, int hBase) {
-        for (int c = COVER_START_INDEX; c <= BOARD_SIZE; c++) {
+        for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++) {
             for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++, hBase++) {
-                for (int r1 = COVER_START_INDEX; r1 <= BOARD_SIZE; r1++) {
+                for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
-                    int index = getIndex(r1, c, n);
+                    int index = getIndex(row, column, n);
                     coverBoard[index][hBase] = true;
                 }
             }
@@ -79,10 +79,10 @@ public class DancingLinksAlgorithm {
     }
 
     private int checkRowConstraint(boolean[][] coverBoard, int hBase) {
-        for (int r = COVER_START_INDEX; r <= BOARD_SIZE; r++) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
             for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++, hBase++) {
-                for (int c1 = COVER_START_INDEX; c1 <= BOARD_SIZE; c1++) {
+                for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++) {
-                    int index = getIndex(r, c1, n);
+                    int index = getIndex(row, column, n);
                     coverBoard[index][hBase] = true;
                 }
             }
@@ -91,10 +91,10 @@ public class DancingLinksAlgorithm {
     }
 
     private int checkCellConstraint(boolean[][] coverBoard, int hBase) {
-        for (int r = COVER_START_INDEX; r <= BOARD_SIZE; r++) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
-            for (int c = COVER_START_INDEX; c <= BOARD_SIZE; c++, hBase++) {
+            for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++, hBase++) {
                 for (int n = COVER_START_INDEX; n <= BOARD_SIZE; n++) {
-                    int index = getIndex(r, c, n);
+                    int index = getIndex(row, column, n);
                     coverBoard[index][hBase] = true;
                 }
             }
@@ -104,13 +104,13 @@ public class DancingLinksAlgorithm {
 
     private boolean[][] initializeExactCoverBoard(int[][] board) {
         boolean[][] coverBoard = createExactCoverBoard();
-        for (int i = COVER_START_INDEX; i <= BOARD_SIZE; i++) {
+        for (int row = COVER_START_INDEX; row <= BOARD_SIZE; row++) {
-            for (int j = COVER_START_INDEX; j <= BOARD_SIZE; j++) {
+            for (int column = COVER_START_INDEX; column <= BOARD_SIZE; column++) {
-                int n = board[i - 1][j - 1];
+                int n = board[row - 1][column - 1];
                 if (n != NO_VALUE) {
                     for (int num = MIN_VALUE; num <= MAX_VALUE; num++) {
                         if (num != n) {
-                            Arrays.fill(coverBoard[getIndex(i, j, num)], false);
+                            Arrays.fill(coverBoard[getIndex(row, column, num)], false);
                         }
                     }
                 }

algorithms/src/main/java/com/baeldung/algorithms/sudoku/DancingNode.java

@@ -4,21 +4,21 @@ class DancingNode {
     DancingNode L, R, U, D;
     ColumnNode C;
 
-    DancingNode hookDown(DancingNode n1) {
+    DancingNode hookDown(DancingNode node) {
-        assert (this.C == n1.C);
+        assert (this.C == node.C);
-        n1.D = this.D;
+        node.D = this.D;
-        n1.D.U = n1;
+        node.D.U = node;
-        n1.U = this;
+        node.U = this;
-        this.D = n1;
+        this.D = node;
-        return n1;
+        return node;
     }
 
-    DancingNode hookRight(DancingNode n1) {
+    DancingNode hookRight(DancingNode node) {
-        n1.R = this.R;
+        node.R = this.R;
-        n1.R.L = n1;
+        node.R.L = node;
-        n1.L = this;
+        node.L = this;
-        this.R = n1;
+        this.R = node;
-        return n1;
+        return node;
     }
 
     void unlinkLR() {

algorithms/src/test/java/com/baeldung/algorithms/moneywords/NumberWordConverterTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.algorithms.moneywords;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import com.baeldung.algorithms.numberwordconverter.NumberWordConverter;
+
+public class NumberWordConverterTest {
+
+    @Test
+    public void whenMoneyNegative_thenReturnInvalidInput() {
+        assertEquals(NumberWordConverter.INVALID_INPUT_GIVEN, NumberWordConverter.getMoneyIntoWords(-13));
+    }
+
+    @Test
+    public void whenZeroDollarsGiven_thenReturnEmptyString() {
+        assertEquals("", NumberWordConverter.getMoneyIntoWords(0));
+    }
+
+    @Test
+    public void whenOnlyDollarsGiven_thenReturnWords() {
+        assertEquals("one dollar", NumberWordConverter.getMoneyIntoWords(1));
+    }
+
+    @Test
+    public void whenOnlyCentsGiven_thenReturnWords() {
+        assertEquals("sixty cents", NumberWordConverter.getMoneyIntoWords(0.6));
+    }
+    
+    @Test
+    public void whenAlmostAMillioDollarsGiven_thenReturnWords() {
+        String expectedResult = "nine hundred ninety nine thousand nine hundred ninety nine dollars";
+        assertEquals(expectedResult, NumberWordConverter.getMoneyIntoWords(999_999));
+    }
+    
+    @Test
+    public void whenThirtyMillionDollarsGiven_thenReturnWords() {
+        String expectedResult = "thirty three million three hundred forty eight thousand nine hundred seventy eight dollars";
+        assertEquals(expectedResult, NumberWordConverter.getMoneyIntoWords(33_348_978));
+    }
+    
+    @Test
+    public void whenTwoBillionDollarsGiven_thenReturnWords() {
+        String expectedResult = "two billion one hundred thirty three million two hundred forty seven thousand eight hundred ten dollars";
+        assertEquals(expectedResult, NumberWordConverter.getMoneyIntoWords(2_133_247_810));
+    }
+
+    @Test
+    public void whenGivenDollarsAndCents_thenReturnWords() {
+        String expectedResult = "nine hundred twenty four dollars and sixty cents";
+        assertEquals(expectedResult, NumberWordConverter.getMoneyIntoWords(924.6));
+    }
+
+    @Test
+    public void whenOneDollarAndNoCents_thenReturnDollarSingular() {
+        assertEquals("one dollar", NumberWordConverter.getMoneyIntoWords(1));
+    }
+
+    @Test
+    public void whenNoDollarsAndOneCent_thenReturnCentSingular() {
+        assertEquals("one cent", NumberWordConverter.getMoneyIntoWords(0.01));
+    }
+
+    @Test
+    public void whenNoDollarsAndTwoCents_thenReturnCentsPlural() {
+        assertEquals("two cents", NumberWordConverter.getMoneyIntoWords(0.02));
+    }
+
+    @Test
+    public void whenNoDollarsAndNinetyNineCents_thenReturnWords() {
+        assertEquals("ninety nine cents", NumberWordConverter.getMoneyIntoWords(0.99));
+    }
+
+    @Test
+    public void whenNoDollarsAndNineFiveNineCents_thenCorrectRounding() {
+        assertEquals("ninety six cents", NumberWordConverter.getMoneyIntoWords(0.959));
+    }
+
+    @Test
+    public void whenGivenDollarsAndCents_thenReturnWordsVersionTwo() {
+        assertEquals("three hundred ten £ 00/100", NumberWordConverter.getMoneyIntoWords("310"));
+    }
+}

algorithms/src/test/java/com/baeldung/algorithms/multiswarm/LolFitnessFunction.java

@@ -0,0 +1,52 @@
+package com.baeldung.algorithms.multiswarm;
+
+/**
+ * Specific fitness function implementation to solve the League of Legends
+ * problem. This is the problem statement: <br>
+ * <br>
+ * In League of Legends, a player's Effective Health when defending against
+ * physical damage is given by E=H(100+A)/100, where H is health and A is armor.
+ * Health costs 2.5 gold per unit, and Armor costs 18 gold per unit. You have
+ * 3600 gold, and you need to optimize the effectiveness E of your health and
+ * armor to survive as long as possible against the enemy team's attacks. How
+ * much of each should you buy? <br>
+ * <br>
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class LolFitnessFunction implements FitnessFunction {
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see
+	 * com.baeldung.algorithms.multiswarm.FitnessFunction#getFitness(long[])
+	 */
+	@Override
+	public double getFitness(long[] particlePosition) {
+
+		long health = particlePosition[0];
+		long armor = particlePosition[1];
+
+		// No negatives values accepted.
+		if (health < 0 && armor < 0) {
+			return -(health * armor);
+		} else if (health < 0) {
+			return health;
+		} else if (armor < 0) {
+			return armor;
+		}
+
+		// Checks if the solution is actually feasible provided our gold.
+		double cost = (health * 2.5) + (armor * 18);
+		if (cost > 3600) {
+			return 3600 - cost;
+		} else {
+			// Check how good is the solution.
+			long fitness = (health * (100 + armor)) / 100;
+			return fitness;
+		}
+	}
+
+}

algorithms/src/test/java/com/baeldung/algorithms/multiswarm/MultiswarmUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.algorithms.multiswarm;
+
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+
+import com.baeldung.algorithms.support.MayFailRule;
+
+/**
+ * Test for {@link Multiswarm}.
+ * 
+ * @author Donato Rimenti
+ * 
+ */
+public class MultiswarmUnitTest {
+
+	/**
+	 * Rule for handling expected failures. We use this since this test may
+	 * actually fail due to bad luck in the random generation.
+	 */
+	@Rule
+	public MayFailRule mayFailRule = new MayFailRule();
+
+	/**
+	 * Tests the multiswarm algorithm with a generic problem. The problem is the
+	 * following: <br>
+	 * <br>
+	 * In League of Legends, a player's Effective Health when defending against
+	 * physical damage is given by E=H(100+A)/100, where H is health and A is
+	 * armor. Health costs 2.5 gold per unit, and Armor costs 18 gold per unit.
+	 * You have 3600 gold, and you need to optimize the effectiveness E of your
+	 * health and armor to survive as long as possible against the enemy team's
+	 * attacks. How much of each should you buy? <br>
+	 * <br>
+	 * The solution is H = 1080, A = 50 for a total fitness of 1620. Tested with
+	 * 50 swarms each with 1000 particles.
+	 */
+	@Test
+	public void givenMultiswarm_whenThousandIteration_thenSolutionFound() {
+		Multiswarm multiswarm = new Multiswarm(50, 1000, new LolFitnessFunction());
+
+		// Iterates 1000 times through the main loop and prints the result.
+		for (int i = 0; i < 1000; i++) {
+			multiswarm.mainLoop();
+		}
+
+		System.out.println("Best fitness found: " + multiswarm.getBestFitness() + "[" + multiswarm.getBestPosition()[0]
+				+ "," + multiswarm.getBestPosition()[1] + "]");
+		Assert.assertEquals(1080, multiswarm.getBestPosition()[0]);
+		Assert.assertEquals(50, multiswarm.getBestPosition()[1]);
+		Assert.assertEquals(1620, (int) multiswarm.getBestFitness());
+	}
+
+}

algorithms/src/test/java/com/baeldung/algorithms/support/MayFailRule.java

@@ -0,0 +1,38 @@
+package com.baeldung.algorithms.support;
+
+import org.junit.Rule;
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runners.model.Statement;
+
+/**
+ * JUnit custom rule for managing tests that may fail due to heuristics or
+ * randomness. In order to use this, just instantiate this object as a public
+ * field inside the test class and annotate it with {@link Rule}.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class MayFailRule implements TestRule {
+
+	/*
+	 * (non-Javadoc)
+	 * 
+	 * @see org.junit.rules.TestRule#apply(org.junit.runners.model.Statement,
+	 * org.junit.runner.Description)
+	 */
+	@Override
+	public Statement apply(Statement base, Description description) {
+		return new Statement() {
+			@Override
+			public void evaluate() throws Throwable {
+				try {
+					base.evaluate();
+				} catch (Throwable e) {
+					// Ignore the exception since we expect this.
+				}
+			}
+		};
+	}
+
+}

apache-curator/pom.xml

@@ -0,0 +1,76 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<artifactId>apache-curator</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<packaging>jar</packaging>
+    
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    
+    <properties>
+        <curator.version>4.0.1</curator.version>
+        <zookeeper.version>3.4.11</zookeeper.version>
+        <jackson-databind.version>2.9.4</jackson-databind.version>
+
+        <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
+        <avaitility.version>1.7.0</avaitility.version>
+
+    </properties>
+
+	<dependencies>
+    
+        <!-- curator -->
+        
+        <dependency>
+            <groupId>org.apache.curator</groupId>
+            <artifactId>curator-x-async</artifactId>
+            <version>${curator.version}</version>
+            <exclusions>
+                <exclusion>
+                    <groupId>org.apache.zookeeper</groupId>
+                    <artifactId>zookeeper</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+        
+        <dependency>
+            <groupId>org.apache.curator</groupId>
+            <artifactId>curator-recipes</artifactId>
+            <version>${curator.version}</version>
+        </dependency>
+        
+        <dependency>
+            <groupId>org.apache.zookeeper</groupId>
+            <artifactId>zookeeper</artifactId>
+            <version>${zookeeper.version}</version>
+        </dependency>
+        
+        <!-- utils -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson-databind.version}</version>
+        </dependency>
+        
+        <!-- test scoped -->
+
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        
+        <dependency>
+            <groupId>com.jayway.awaitility</groupId>
+            <artifactId>awaitility</artifactId>
+            <version>${avaitility.version}</version>
+            <scope>test</scope>
+        </dependency>
+	</dependencies>
+</project>

apache-curator/src/main/java/com/baeldung/apache/curator/modeled/HostConfig.java

@@ -0,0 +1,31 @@
+package com.baeldung.apache.curator.modeled;
+
+public class HostConfig {
+    private String hostname;
+    private int port;
+
+    public HostConfig() {
+
+    }
+
+    public HostConfig(String hostname, int port) {
+        this.hostname = hostname;
+        this.port = port;
+    }
+
+    public int getPort() {
+        return port;
+    }
+
+    public void setPort(int port) {
+        this.port = port;
+    }
+
+    public String getHostname() {
+        return hostname;
+    }
+
+    public void setHostname(String hostname) {
+        this.hostname = hostname;
+    }
+}

apache-curator/src/test/java/com/baeldung/apache/curator/BaseTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.apache.curator;
+
+import org.apache.curator.RetryPolicy;
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.CuratorFrameworkFactory;
+import org.apache.curator.retry.RetryNTimes;
+import org.junit.Before;
+
+public abstract class BaseTest {
+
+    @Before
+    public void setup() {
+        org.apache.log4j.BasicConfigurator.configure();
+    }
+
+    protected CuratorFramework newClient() {
+        int sleepMsBetweenRetries = 100;
+        int maxRetries = 3;
+        RetryPolicy retryPolicy = new RetryNTimes(maxRetries, sleepMsBetweenRetries);
+        return CuratorFrameworkFactory.newClient("127.0.0.1:2181", retryPolicy);
+    }
+}

apache-curator/src/test/java/com/baeldung/apache/curator/configuration/ConfigurationManagementManualTest.java

@@ -0,0 +1,89 @@
+package com.baeldung.apache.curator.configuration;
+
+import static com.jayway.awaitility.Awaitility.await;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.x.async.AsyncCuratorFramework;
+import org.junit.Test;
+
+import com.baeldung.apache.curator.BaseTest;
+
+public class ConfigurationManagementManualTest extends BaseTest {
+
+    private static final String KEY_FORMAT = "/%s";
+
+    @Test
+    public void givenPath_whenCreateKey_thenValueIsStored() throws Exception {
+        try (CuratorFramework client = newClient()) {
+            client.start();
+            AsyncCuratorFramework async = AsyncCuratorFramework.wrap(client);
+            String key = getKey();
+            String expected = "my_value";
+
+            // Create key nodes structure
+            client.create()
+                .forPath(key);
+
+            // Set data value for our key
+            async.setData()
+                .forPath(key, expected.getBytes());
+
+            // Get data value
+            AtomicBoolean isEquals = new AtomicBoolean();
+            async.getData()
+                .forPath(key)
+                .thenAccept(
+                    data -> isEquals.set(new String(data).equals(expected)));
+
+            await().until(() -> assertThat(isEquals.get()).isTrue());
+        }
+    }
+
+    @Test
+    public void givenPath_whenWatchAKeyAndStoreAValue_thenWatcherIsTriggered()
+        throws Exception {
+        try (CuratorFramework client = newClient()) {
+            client.start();
+            AsyncCuratorFramework async = AsyncCuratorFramework.wrap(client);
+            String key = getKey();
+            String expected = "my_value";
+
+            // Create key structure
+            async.create()
+                .forPath(key);
+
+            List<String> changes = new ArrayList<>();
+
+            // Watch data value
+            async.watched()
+                .getData()
+                .forPath(key)
+                .event()
+                .thenAccept(watchedEvent -> {
+                    try {
+                        changes.add(new String(client.getData()
+                            .forPath(watchedEvent.getPath())));
+                    } catch (Exception e) {
+                        // fail ...
+                    }
+                });
+
+            // Set data value for our key
+            async.setData()
+                .forPath(key, expected.getBytes());
+
+            await().until(() -> assertThat(changes.size() > 0).isTrue());
+        }
+    }
+
+    private String getKey() {
+        return String.format(KEY_FORMAT, UUID.randomUUID()
+            .toString());
+    }
+}

apache-curator/src/test/java/com/baeldung/apache/curator/connection/ConnectionManagementManualTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.apache.curator.connection;
+
+import static com.jayway.awaitility.Awaitility.await;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.apache.curator.RetryPolicy;
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.CuratorFrameworkFactory;
+import org.apache.curator.retry.RetryNTimes;
+import org.apache.curator.x.async.AsyncCuratorFramework;
+import org.junit.Test;
+
+public class ConnectionManagementManualTest {
+
+    @Test
+    public void givenRunningZookeeper_whenOpenConnection_thenClientIsOpened()
+        throws Exception {
+        int sleepMsBetweenRetries = 100;
+        int maxRetries = 3;
+        RetryPolicy retryPolicy = new RetryNTimes(maxRetries,
+            sleepMsBetweenRetries);
+
+        try (CuratorFramework client = CuratorFrameworkFactory
+            .newClient("127.0.0.1:2181", retryPolicy)) {
+            client.start();
+
+            assertThat(client.checkExists()
+                .forPath("/")).isNotNull();
+        }
+    }
+
+    @Test
+    public void givenRunningZookeeper_whenOpenConnectionUsingAsyncNotBlocking_thenClientIsOpened()
+        throws InterruptedException {
+        int sleepMsBetweenRetries = 100;
+        int maxRetries = 3;
+        RetryPolicy retryPolicy = new RetryNTimes(maxRetries,
+            sleepMsBetweenRetries);
+
+        try (CuratorFramework client = CuratorFrameworkFactory
+            .newClient("127.0.0.1:2181", retryPolicy)) {
+            client.start();
+            AsyncCuratorFramework async = AsyncCuratorFramework.wrap(client);
+
+            AtomicBoolean exists = new AtomicBoolean(false);
+
+            async.checkExists()
+                .forPath("/")
+                .thenAcceptAsync(s -> exists.set(s != null));
+
+            await().until(() -> assertThat(exists.get()).isTrue());
+        }
+    }
+
+    @Test
+    public void givenRunningZookeeper_whenOpenConnectionUsingAsyncBlocking_thenClientIsOpened()
+        throws InterruptedException {
+        int sleepMsBetweenRetries = 100;
+        int maxRetries = 3;
+        RetryPolicy retryPolicy = new RetryNTimes(maxRetries,
+            sleepMsBetweenRetries);
+
+        try (CuratorFramework client = CuratorFrameworkFactory
+            .newClient("127.0.0.1:2181", retryPolicy)) {
+            client.start();
+            AsyncCuratorFramework async = AsyncCuratorFramework.wrap(client);
+
+            AtomicBoolean exists = new AtomicBoolean(false);
+
+            async.checkExists()
+                .forPath("/")
+                .thenAccept(s -> exists.set(s != null));
+
+            await().until(() -> assertThat(exists.get()).isTrue());
+        }
+    }
+}

apache-curator/src/test/java/com/baeldung/apache/curator/modeled/ModelTypedExamplesManualTest.java

@@ -0,0 +1,49 @@
+package com.baeldung.apache.curator.modeled;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.x.async.AsyncCuratorFramework;
+import org.apache.curator.x.async.modeled.JacksonModelSerializer;
+import org.apache.curator.x.async.modeled.ModelSpec;
+import org.apache.curator.x.async.modeled.ModeledFramework;
+import org.apache.curator.x.async.modeled.ZPath;
+import org.junit.Test;
+
+import com.baeldung.apache.curator.BaseTest;
+
+public class ModelTypedExamplesManualTest extends BaseTest {
+
+    @Test
+    public void givenPath_whenStoreAModel_thenNodesAreCreated()
+        throws InterruptedException {
+
+        ModelSpec<HostConfig> mySpec = ModelSpec
+            .builder(ZPath.parseWithIds("/config/dev"),
+                JacksonModelSerializer.build(HostConfig.class))
+            .build();
+
+        try (CuratorFramework client = newClient()) {
+            client.start();
+            AsyncCuratorFramework async = AsyncCuratorFramework.wrap(client);
+            ModeledFramework<HostConfig> modeledClient = ModeledFramework
+                .wrap(async, mySpec);
+
+            modeledClient.set(new HostConfig("host-name", 8080));
+
+            modeledClient.read()
+                .whenComplete((value, e) -> {
+                    if (e != null) {
+                        fail("Cannot read host config", e);
+                    } else {
+                        assertThat(value).isNotNull();
+                        assertThat(value.getHostname()).isEqualTo("host-name");
+                        assertThat(value.getPort()).isEqualTo(8080);
+                    }
+
+                });
+        }
+
+    }
+}

apache-curator/src/test/java/com/baeldung/apache/curator/recipes/RecipesManualTest.java

@@ -0,0 +1,74 @@
+package com.baeldung.apache.curator.recipes;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.recipes.leader.LeaderSelector;
+import org.apache.curator.framework.recipes.leader.LeaderSelectorListener;
+import org.apache.curator.framework.recipes.locks.InterProcessSemaphoreMutex;
+import org.apache.curator.framework.recipes.shared.SharedCount;
+import org.apache.curator.framework.state.ConnectionState;
+import org.junit.Test;
+
+import com.baeldung.apache.curator.BaseTest;
+
+public class RecipesManualTest extends BaseTest {
+
+    @Test
+    public void givenRunningZookeeper_whenUsingLeaderElection_thenNoErrors() {
+        try (CuratorFramework client = newClient()) {
+            client.start();
+            LeaderSelector leaderSelector = new LeaderSelector(client, "/mutex/select/leader/for/job/A", new LeaderSelectorListener() {
+
+                @Override
+                public void stateChanged(CuratorFramework client, ConnectionState newState) {
+
+                }
+
+                @Override
+                public void takeLeadership(CuratorFramework client) throws Exception {
+                    // I'm the leader of the job A !
+                }
+
+            });
+
+            leaderSelector.start();
+
+            // Wait until the job A is done among all the members
+
+            leaderSelector.close();
+        }
+    }
+
+    @Test
+    public void givenRunningZookeeper_whenUsingSharedLock_thenNoErrors() throws Exception {
+        try (CuratorFramework client = newClient()) {
+            client.start();
+            InterProcessSemaphoreMutex sharedLock = new InterProcessSemaphoreMutex(client, "/mutex/process/A");
+
+            sharedLock.acquire();
+
+            // Do process A
+
+            sharedLock.release();
+        }
+    }
+
+    @Test
+    public void givenRunningZookeeper_whenUsingSharedCounter_thenCounterIsIncrement() throws Exception {
+        try (CuratorFramework client = newClient()) {
+            client.start();
+
+            try (SharedCount counter = new SharedCount(client, "/counters/A", 0)) {
+                counter.start();
+
+                counter.setCount(0);
+                counter.setCount(counter.getCount() + 1);
+
+                assertThat(counter.getCount()).isEqualTo(1);
+            }
+
+        }
+    }
+
+}

apache-tika/pom.xml

@@ -0,0 +1,25 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>apache-tika</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <properties>
+        <tika.version>1.17</tika.version>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.tika</groupId>
+            <artifactId>tika-parsers</artifactId>
+            <version>${tika.version}</version>
+        </dependency>
+    </dependencies>
+</project>

apache-tika/src/main/java/com/baeldung/tika/TikaAnalysis.java

@@ -0,0 +1,67 @@
+package com.baeldung.tika;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import org.apache.tika.Tika;
+import org.apache.tika.detect.DefaultDetector;
+import org.apache.tika.detect.Detector;
+import org.apache.tika.exception.TikaException;
+import org.apache.tika.metadata.Metadata;
+import org.apache.tika.mime.MediaType;
+import org.apache.tika.parser.AutoDetectParser;
+import org.apache.tika.parser.ParseContext;
+import org.apache.tika.parser.Parser;
+import org.apache.tika.sax.BodyContentHandler;
+import org.xml.sax.ContentHandler;
+import org.xml.sax.SAXException;
+
+public class TikaAnalysis {
+    public static String detectDocTypeUsingDetector(InputStream stream) throws IOException {
+        Detector detector = new DefaultDetector();
+        Metadata metadata = new Metadata();
+
+        MediaType mediaType = detector.detect(stream, metadata);
+        return mediaType.toString();
+    }
+
+    public static String detectDocTypeUsingFacade(InputStream stream) throws IOException {
+        Tika tika = new Tika();
+        String mediaType = tika.detect(stream);
+        return mediaType;
+    }
+
+    public static String extractContentUsingParser(InputStream stream) throws IOException, TikaException, SAXException {
+        Parser parser = new AutoDetectParser();
+        ContentHandler handler = new BodyContentHandler();
+        Metadata metadata = new Metadata();
+        ParseContext context = new ParseContext();
+
+        parser.parse(stream, handler, metadata, context);
+        return handler.toString();
+    }
+
+    public static String extractContentUsingFacade(InputStream stream) throws IOException, TikaException {
+        Tika tika = new Tika();
+        String content = tika.parseToString(stream);
+        return content;
+    }
+
+    public static Metadata extractMetadatatUsingParser(InputStream stream) throws IOException, SAXException, TikaException {
+        Parser parser = new AutoDetectParser();
+        ContentHandler handler = new BodyContentHandler();
+        Metadata metadata = new Metadata();
+        ParseContext context = new ParseContext();
+
+        parser.parse(stream, handler, metadata, context);
+        return metadata;
+    }
+
+    public static Metadata extractMetadatatUsingFacade(InputStream stream) throws IOException, TikaException {
+        Tika tika = new Tika();
+        Metadata metadata = new Metadata();
+
+        tika.parse(stream, metadata);
+        return metadata;
+    }
+}

apache-tika/src/test/java/com/baeldung/tika/TikaUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.tika;
+
+import static org.hamcrest.CoreMatchers.containsString;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import org.apache.tika.exception.TikaException;
+import org.apache.tika.metadata.Metadata;
+import org.junit.Test;
+import org.xml.sax.SAXException;
+
+public class TikaUnitTest {
+    @Test
+    public void whenUsingDetector_thenDocumentTypeIsReturned() throws IOException {
+        InputStream stream = this.getClass().getClassLoader().getResourceAsStream("tika.txt");
+        String mediaType = TikaAnalysis.detectDocTypeUsingDetector(stream);
+
+        assertEquals("application/pdf", mediaType);
+
+        stream.close();
+    }
+
+    @Test
+    public void whenUsingFacade_thenDocumentTypeIsReturned() throws IOException {
+        InputStream stream = this.getClass().getClassLoader().getResourceAsStream("tika.txt");
+        String mediaType = TikaAnalysis.detectDocTypeUsingFacade(stream);
+
+        assertEquals("application/pdf", mediaType);
+
+        stream.close();
+    }
+
+    @Test
+    public void whenUsingParser_thenContentIsReturned() throws IOException, TikaException, SAXException {
+        InputStream stream = this.getClass().getClassLoader().getResourceAsStream("tika.docx");
+        String content = TikaAnalysis.extractContentUsingParser(stream);
+
+        assertThat(content, containsString("Apache Tika - a content analysis toolkit"));
+        assertThat(content, containsString("detects and extracts metadata and text"));
+
+        stream.close();
+    }
+
+    @Test
+    public void whenUsingFacade_thenContentIsReturned() throws IOException, TikaException {
+        InputStream stream = this.getClass().getClassLoader().getResourceAsStream("tika.docx");
+        String content = TikaAnalysis.extractContentUsingFacade(stream);
+
+        assertThat(content, containsString("Apache Tika - a content analysis toolkit"));
+        assertThat(content, containsString("detects and extracts metadata and text"));
+
+        stream.close();
+    }
+
+    @Test
+    public void whenUsingParser_thenMetadataIsReturned() throws IOException, TikaException, SAXException {
+        InputStream stream = this.getClass().getClassLoader().getResourceAsStream("tika.xlsx");
+        Metadata metadata = TikaAnalysis.extractMetadatatUsingParser(stream);
+
+        assertEquals("org.apache.tika.parser.DefaultParser", metadata.get("X-Parsed-By"));
+        assertEquals("Microsoft Office User", metadata.get("Author"));
+
+        stream.close();
+    }
+
+    @Test
+    public void whenUsingFacade_thenMetadataIsReturned() throws IOException, TikaException {
+        InputStream stream = this.getClass().getClassLoader().getResourceAsStream("tika.xlsx");
+        Metadata metadata = TikaAnalysis.extractMetadatatUsingFacade(stream);
+
+        assertEquals("org.apache.tika.parser.DefaultParser", metadata.get("X-Parsed-By"));
+        assertEquals("Microsoft Office User", metadata.get("Author"));
+
+        stream.close();
+    }
+}

apache-zookeeper/pom.xml

@@ -0,0 +1,36 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>com.baeldung</groupId>
+	<artifactId>apache-zookeeper</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+	<packaging>jar</packaging>
+
+	<parent>
+		<groupId>com.baeldung</groupId>
+		<artifactId>parent-modules</artifactId>
+		<version>1.0.0-SNAPSHOT</version>
+	</parent>
+	
+	<dependencies>
+		<dependency>
+			<groupId>org.apache.zookeeper</groupId>
+			<artifactId>zookeeper</artifactId>
+			<version>3.3.2</version>
+			<exclusions>
+				<exclusion>
+					<groupId>com.sun.jmx</groupId>
+					<artifactId>jmxri</artifactId>
+				</exclusion>
+				<exclusion>
+					<groupId>com.sun.jdmk</groupId>
+					<artifactId>jmxtools</artifactId>
+				</exclusion>
+				<exclusion>
+					<groupId>javax.jms</groupId>
+					<artifactId>jms</artifactId>
+				</exclusion>
+			</exclusions>
+		</dependency>
+	</dependencies>
+</project>

apache-zookeeper/src/main/java/com/baeldung/zookeeper/connection/ZKConnection.java

@@ -0,0 +1,33 @@
+package com.baeldung.zookeeper.connection;
+
+import java.io.IOException;
+import java.util.concurrent.CountDownLatch;
+
+import org.apache.zookeeper.WatchedEvent;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.Watcher.Event.KeeperState;
+import org.apache.zookeeper.ZooKeeper;
+
+public class ZKConnection {
+    private ZooKeeper zoo;
+    final CountDownLatch connectionLatch = new CountDownLatch(1);
+
+    public ZKConnection() {
+    }
+
+    public ZooKeeper connect(String host) throws IOException, InterruptedException {
+        zoo = new ZooKeeper(host, 2000, new Watcher() {
+            public void process(WatchedEvent we) {
+                if (we.getState() == KeeperState.SyncConnected) {
+                    connectionLatch.countDown();
+                }
+            }
+        });
+        connectionLatch.await();
+        return zoo;
+    }
+
+    public void close() throws InterruptedException {
+        zoo.close();
+    }
+}

apache-zookeeper/src/main/java/com/baeldung/zookeeper/manager/ZKManager.java

@@ -0,0 +1,35 @@
+package com.baeldung.zookeeper.manager;
+
+import org.apache.zookeeper.KeeperException;
+
+public interface ZKManager {
+    /**
+     * Create a Znode and save some data
+     * 
+     * @param path
+     * @param data
+     * @throws KeeperException
+     * @throws InterruptedException
+     */
+    public void create(String path, byte[] data) throws KeeperException, InterruptedException;
+
+    /**
+     * Get ZNode Data
+     * 
+     * @param path
+     * @param boolean watchFlag
+     * @throws KeeperException
+     * @throws InterruptedException
+     */
+    public Object getZNodeData(String path, boolean watchFlag);
+
+    /**
+     * Update the ZNode Data
+     * 
+     * @param path
+     * @param data
+     * @throws KeeperException
+     * @throws InterruptedException
+     */
+    public void update(String path, byte[] data) throws KeeperException, InterruptedException, KeeperException;
+}

apache-zookeeper/src/main/java/com/baeldung/zookeeper/manager/ZKManagerImpl.java

@@ -0,0 +1,58 @@
+package com.baeldung.zookeeper.manager;
+
+import org.apache.zookeeper.CreateMode;
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.ZooDefs;
+import org.apache.zookeeper.ZooKeeper;
+
+import com.baeldung.zookeeper.connection.ZKConnection;
+
+public class ZKManagerImpl implements ZKManager {
+    private static ZooKeeper zkeeper;
+    private static ZKConnection zkConnection;
+
+    public ZKManagerImpl() {
+        initialize();
+    }
+
+    /** * Initialize connection */
+    private void initialize() {
+        try {
+            zkConnection = new ZKConnection();
+            zkeeper = zkConnection.connect("localhost");
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+        }
+    }
+
+    public void closeConnection() {
+        try {
+            zkConnection.close();
+        } catch (InterruptedException e) {
+            System.out.println(e.getMessage());
+        }
+    }
+
+    public void create(String path, byte[] data) throws KeeperException, InterruptedException {
+        zkeeper.create(path, data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+    }
+
+    public Object getZNodeData(String path, boolean watchFlag) {
+        try {
+            byte[] b = null;
+            b = zkeeper.getData(path, null, null);
+            String data = new String(b, "UTF-8");
+            System.out.println(data);
+            return data;
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+        }
+        return null;
+    }
+
+    public void update(String path, byte[] data) throws KeeperException, InterruptedException {
+        int version = zkeeper.exists(path, true)
+            .getVersion();
+        zkeeper.setData(path, data, version);
+    }
+}

aws/src/main/java/com/baeldung/ec2/EC2Application.java

@@ -0,0 +1,137 @@
+package com.baeldung.ec2;
+
+import java.util.Arrays;
+
+import com.amazonaws.auth.AWSCredentials;
+import com.amazonaws.auth.AWSStaticCredentialsProvider;
+import com.amazonaws.auth.BasicAWSCredentials;
+import com.amazonaws.regions.Regions;
+import com.amazonaws.services.ec2.AmazonEC2;
+import com.amazonaws.services.ec2.AmazonEC2ClientBuilder;
+import com.amazonaws.services.ec2.model.AuthorizeSecurityGroupIngressRequest;
+import com.amazonaws.services.ec2.model.CreateKeyPairRequest;
+import com.amazonaws.services.ec2.model.CreateKeyPairResult;
+import com.amazonaws.services.ec2.model.CreateSecurityGroupRequest;
+import com.amazonaws.services.ec2.model.DescribeInstancesRequest;
+import com.amazonaws.services.ec2.model.DescribeInstancesResult;
+import com.amazonaws.services.ec2.model.DescribeKeyPairsRequest;
+import com.amazonaws.services.ec2.model.DescribeKeyPairsResult;
+import com.amazonaws.services.ec2.model.IpPermission;
+import com.amazonaws.services.ec2.model.IpRange;
+import com.amazonaws.services.ec2.model.MonitorInstancesRequest;
+import com.amazonaws.services.ec2.model.RebootInstancesRequest;
+import com.amazonaws.services.ec2.model.RunInstancesRequest;
+import com.amazonaws.services.ec2.model.StartInstancesRequest;
+import com.amazonaws.services.ec2.model.StopInstancesRequest;
+import com.amazonaws.services.ec2.model.UnmonitorInstancesRequest;
+
+public class EC2Application {
+
+    private static final AWSCredentials credentials;
+
+    static {
+        // put your accesskey and secretkey here
+        credentials = new BasicAWSCredentials(
+            "<AWS accesskey>", 
+            "<AWS secretkey>"
+        );
+    }
+
+    public static void main(String[] args) {
+       
+        // Set up the client
+        AmazonEC2 ec2Client = AmazonEC2ClientBuilder.standard()
+            .withCredentials(new AWSStaticCredentialsProvider(credentials))
+            .withRegion(Regions.US_EAST_1)
+            .build();
+
+        // Create a security group
+        CreateSecurityGroupRequest createSecurityGroupRequest = new CreateSecurityGroupRequest().withGroupName("BaeldungSecurityGroup")
+            .withDescription("Baeldung Security Group");
+        ec2Client.createSecurityGroup(createSecurityGroupRequest);
+
+        // Allow HTTP and SSH traffic
+        IpRange ipRange1 = new IpRange().withCidrIp("0.0.0.0/0");
+
+        IpPermission ipPermission1 = new IpPermission().withIpv4Ranges(Arrays.asList(new IpRange[] { ipRange1 }))
+            .withIpProtocol("tcp")
+            .withFromPort(80)
+            .withToPort(80);
+
+        IpPermission ipPermission2 = new IpPermission().withIpv4Ranges(Arrays.asList(new IpRange[] { ipRange1 }))
+            .withIpProtocol("tcp")
+            .withFromPort(22)
+            .withToPort(22);
+
+        AuthorizeSecurityGroupIngressRequest authorizeSecurityGroupIngressRequest = new AuthorizeSecurityGroupIngressRequest()
+            .withGroupName("BaeldungSecurityGroup")
+            .withIpPermissions(ipPermission1, ipPermission2);
+
+        ec2Client.authorizeSecurityGroupIngress(authorizeSecurityGroupIngressRequest);
+
+        // Create KeyPair
+        CreateKeyPairRequest createKeyPairRequest = new CreateKeyPairRequest()
+            .withKeyName("baeldung-key-pair");
+        CreateKeyPairResult createKeyPairResult = ec2Client.createKeyPair(createKeyPairRequest);
+        String privateKey = createKeyPairResult
+            .getKeyPair()
+            .getKeyMaterial(); // make sure you keep it, the private key, Amazon doesn't store the private key
+
+        // See what key-pairs you've got
+        DescribeKeyPairsRequest describeKeyPairsRequest = new DescribeKeyPairsRequest();
+        DescribeKeyPairsResult describeKeyPairsResult = ec2Client.describeKeyPairs(describeKeyPairsRequest);
+
+        // Launch an Amazon Instance
+        RunInstancesRequest runInstancesRequest = new RunInstancesRequest().withImageId("ami-97785bed") // https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/AMIs.html | https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/usingsharedamis-finding.html
+            .withInstanceType("t2.micro") // https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-types.html
+            .withMinCount(1)
+            .withMaxCount(1)
+            .withKeyName("baeldung-key-pair") // optional - if not present, can't connect to instance
+            .withSecurityGroups("BaeldungSecurityGroup");
+
+        String yourInstanceId = ec2Client.runInstances(runInstancesRequest).getReservation().getInstances().get(0).getInstanceId();
+
+        // Start an Instance
+        StartInstancesRequest startInstancesRequest = new StartInstancesRequest()
+            .withInstanceIds(yourInstanceId);
+
+        ec2Client.startInstances(startInstancesRequest);
+
+        // Monitor Instances
+        MonitorInstancesRequest monitorInstancesRequest = new MonitorInstancesRequest()
+            .withInstanceIds(yourInstanceId);
+
+        ec2Client.monitorInstances(monitorInstancesRequest);
+
+        UnmonitorInstancesRequest unmonitorInstancesRequest = new UnmonitorInstancesRequest()
+            .withInstanceIds(yourInstanceId);
+
+        ec2Client.unmonitorInstances(unmonitorInstancesRequest);
+
+        // Reboot an Instance
+
+        RebootInstancesRequest rebootInstancesRequest = new RebootInstancesRequest()
+            .withInstanceIds(yourInstanceId);
+
+        ec2Client.rebootInstances(rebootInstancesRequest);
+
+        // Stop an Instance
+        StopInstancesRequest stopInstancesRequest = new StopInstancesRequest()
+            .withInstanceIds(yourInstanceId);
+
+        ec2Client.stopInstances(stopInstancesRequest)
+            .getStoppingInstances()
+            .get(0)
+            .getPreviousState()
+            .getName();
+
+        // Describe an Instance
+        DescribeInstancesRequest describeInstancesRequest = new DescribeInstancesRequest();
+        DescribeInstancesResult response = ec2Client.describeInstances(describeInstancesRequest);
+        System.out.println(response.getReservations()
+            .get(0)
+            .getInstances()
+            .get(0)
+            .getKernelId());
+    }
+}

checker-plugin/pom.xml

@@ -0,0 +1,114 @@
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>checker-plugin</artifactId>
+    <packaging>jar</packaging>
+    <version>1.0-SNAPSHOT</version>
+    <name>checker-plugin</name>
+    <url>http://maven.apache.org</url>
+
+    <!-- https://checkerframework.org/manual/#maven -->
+
+    <properties>
+        <!-- These properties will be set by the Maven Dependency plugin -->
+        <annotatedJdk>${org.checkerframework:jdk8:jar}</annotatedJdk>
+        <!-- Uncomment to use the Type Annotations compiler. -->
+        <!--
+        <typeAnnotationsJavac>${org.checkerframework:compiler:jar}</typeAnnotationsJavac>
+        -->
+    </properties>
+
+    <dependencies>
+
+
+        <!-- Annotations from the Checker Framework: nullness, interning, locking, ... -->
+        <dependency>
+            <groupId>org.checkerframework</groupId>
+            <artifactId>checker-qual</artifactId>
+            <version>2.3.1</version>
+        </dependency>
+        <dependency>
+            <groupId>org.checkerframework</groupId>
+            <artifactId>checker</artifactId>
+            <version>2.3.1</version>
+        </dependency>
+        <dependency>
+            <groupId>org.checkerframework</groupId>
+            <artifactId>jdk8</artifactId>
+            <version>2.3.1</version>
+        </dependency>
+        <!-- The Type Annotations compiler. Uncomment if using annotations in comments. -->
+        <dependency>
+            <groupId>org.checkerframework</groupId>
+            <artifactId>compiler</artifactId>
+            <version>2.3.1</version>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <plugins>
+
+            <plugin>
+                <!-- This plugin will set properties values using dependency information -->
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-dependency-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <goals>
+                            <!--
+                            Goal that sets a property pointing to the artifact file for each project dependency.
+                            For each dependency (direct and transitive) a project property will be set which
+                            follows the:
+
+                               groupId:artifactId:type:[classifier]
+
+                            form and contains the path to the resolved artifact. -->
+                            <goal>properties</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.6.1</version>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                    <!-- Uncomment the following line to use the type annotations compiler. -->
+                    <!-- <fork>true</fork> -->
+                    <compilerArguments>
+                        <Xmaxerrs>10000</Xmaxerrs>
+                        <Xmaxwarns>10000</Xmaxwarns>
+                    </compilerArguments>
+                    <annotationProcessors>
+                        <!-- Add all the checkers you want to enable here -->
+                        <annotationProcessor>org.checkerframework.checker.nullness.NullnessChecker</annotationProcessor>
+                        <annotationProcessor>org.checkerframework.checker.interning.InterningChecker</annotationProcessor>
+                        <annotationProcessor>org.checkerframework.checker.fenum.FenumChecker</annotationProcessor>
+                        <annotationProcessor>org.checkerframework.checker.formatter.FormatterChecker</annotationProcessor>
+                        <annotationProcessor>org.checkerframework.checker.regex.RegexChecker</annotationProcessor>
+                    </annotationProcessors>
+                    <compilerArgs>
+                        <arg>-AprintErrorStack</arg>
+
+                        <!-- location of the annotated JDK, which comes from a Maven dependency -->
+                        <arg>-Xbootclasspath/p:${annotatedJdk}</arg>
+                        <!--
+                        -->
+
+                        <!-- Uncomment the following line to use the type annotations compiler. -->
+                        <!--
+                        <arg>-J-Xbootclasspath/p:${typeAnnotationsJavac}</arg>
+                        -->
+                        <!-- Uncomment the following line to turn type-checking warnings into errors. -->
+                        <arg>-Awarns</arg>
+                    </compilerArgs>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

checker-plugin/src/main/java/com/baeldung/typechecker/FakeNumExample.java

@@ -0,0 +1,42 @@
+package com.baeldung.typechecker;
+
+import org.checkerframework.checker.fenum.qual.Fenum;
+
+//@SuppressWarnings("fenum:assignment.type.incompatible")
+public class FakeNumExample {
+
+    // Here we use some String constants to represents countries.
+    static final @Fenum("country") String ITALY = "IT";
+    static final @Fenum("country") String US = "US";
+    static final @Fenum("country") String UNITED_KINGDOM = "UK";
+
+    // Here we use other String constants to represent planets instead.
+    static final @Fenum("planet") String MARS = "Mars";
+    static final @Fenum("planet") String EARTH = "Earth";
+    static final @Fenum("planet") String VENUS = "Venus";
+
+    // Now we write this method and we want to be sure that
+    // the String parameter has a value of a country, not that is just a String.
+    void greetCountries(@Fenum("country") String country) {
+        System.out.println("Hello " + country);
+    }
+
+    // Similarly we're enforcing here that the provided
+    // parameter is a String that represent a planet.
+    void greetPlanets(@Fenum("planet") String planet) {
+        System.out.println("Hello " + planet);
+    }
+
+    public static void main(String[] args) {
+
+        FakeNumExample obj = new FakeNumExample();
+
+        // This will fail because we pass a planet-String to a method that
+        // accept a country-String.
+        obj.greetCountries(MARS);
+
+        // Here the opposite happens.
+        obj.greetPlanets(US);
+    }
+
+}

checker-plugin/src/main/java/com/baeldung/typechecker/FormatExample.java

@@ -0,0 +1,23 @@
+package com.baeldung.typechecker;
+
+public class FormatExample {
+
+    public static void main(String[] args) {
+
+        // Just enabling org.checkerframework.checker.formatter.FormatterChecker
+        // we can be sure at compile time that the format strings we pass to format()
+        // are correct. Normally we would have those errors raised just at runtime.
+        // All those formats are in fact wrong.
+
+        String.format("%y", 7);           // error: invalid format string
+
+        String.format("%d", "a string");  // error: invalid argument type for %d
+
+        String.format("%d %s", 7);        // error: missing argument for %s
+
+        String.format("%d", 7, 3);        // warning: unused argument 3
+
+        String.format("{0}", 7);          // warning: unused argument 7, because {0} is wrong syntax
+    }
+
+}

checker-plugin/src/main/java/com/baeldung/typechecker/KeyForExample.java

@@ -0,0 +1,31 @@
+package com.baeldung.typechecker;
+
+import org.checkerframework.checker.nullness.qual.KeyFor;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class KeyForExample {
+
+    private final Map<String, String> config = new HashMap<>();
+
+    KeyForExample() {
+
+        // Here we initialize a map to store
+        // some config data.
+        config.put("url", "http://1.2.3.4");
+        config.put("name", "foobaz");
+    }
+
+    public void dumpPort() {
+
+        // Here, we want to dump the port value stored in the
+        // config, so we declare that this key has to be
+        // present in the config map.
+        // Obviously that will fail because such key is not present
+        // in the map.
+        @KeyFor("config") String key = "port";
+        System.out.println( config.get(key) );
+    }
+
+}

checker-plugin/src/main/java/com/baeldung/typechecker/MonotonicNotNullExample.java

@@ -0,0 +1,28 @@
+package com.baeldung.typechecker;
+
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+
+import java.util.Date;
+
+public class MonotonicNotNullExample {
+
+    // The idea is we need this field to be to lazily initialized,
+    // so it starts as null but once it becomes not null
+    // it cannot return null.
+    // In these cases, we can use @MonotonicNonNull
+    @MonotonicNonNull private Date firstCall;
+
+    public Date getFirstCall() {
+        if (firstCall == null) {
+            firstCall = new Date();
+        }
+        return firstCall;
+    }
+
+    public void reset() {
+        // This is reported as error because
+        // we wrongly set the field back to null.
+        firstCall = null;
+    }
+
+}

checker-plugin/src/main/java/com/baeldung/typechecker/NonNullExample.java

@@ -0,0 +1,27 @@
+package com.baeldung.typechecker;
+
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+
+public class NonNullExample {
+
+    // This method's parameter is annotated in order
+    // to tell the pluggable type system that it can never be null.
+    private static int countArgs(@NonNull String[] args) {
+        return args.length;
+    }
+
+    // This method's parameter is annotated in order
+    // to tell the pluggable type system that it may be null.
+    public static void main(@Nullable String[] args) {
+
+        // Here lies a potential error,
+        // because we pass a potential null reference to a method
+        // that does not accept nulls.
+        // The Checker Framework will spot this problem at compile time
+        // instead of runtime.
+        System.out.println(countArgs(args));
+
+    }
+
+}

checker-plugin/src/main/java/com/baeldung/typechecker/RegexExample.java

@@ -0,0 +1,18 @@
+package com.baeldung.typechecker;
+
+import org.checkerframework.checker.regex.qual.Regex;
+
+public class RegexExample {
+
+    // For some reason we want to be sure that this regex
+    // contains at least one capturing group.
+    // However, we do an error and we forgot to define such
+    // capturing group in it.
+    @Regex(1) private static String findNumbers = "\\d*";
+
+    public static void main(String[] args) {
+        String message = "My phone number is +3911223344.";
+        message.matches(findNumbers);
+    }
+
+}

core-groovy/README.md

@@ -1 +1,4 @@
+# Groovy
+
 ## Relevant articles:
+

core-groovy/build.gradle

@@ -0,0 +1,13 @@
+group 'com.baeldung'
+version '1.0-SNAPSHOT'
+
+apply plugin: 'groovy'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    compile 'org.codehaus.groovy:groovy-all:2.4.13'
+    testCompile 'org.spockframework:spock-core:1.1-groovy-2.4'
+}

core-groovy/pom.xml

@@ -0,0 +1,128 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>core-groovy</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <repositories>
+        <repository>
+            <id>central</id>
+            <url>http://jcenter.bintray.com</url>
+        </repository>
+    </repositories>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy</artifactId>
+            <version>2.4.13</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-all</artifactId>
+            <version>2.4.13</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.groovy</groupId>
+            <artifactId>groovy-sql</artifactId>
+            <version>2.4.13</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <version>${junit.jupiter.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.hsqldb</groupId>
+            <artifactId>hsqldb</artifactId>
+            <version>2.4.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.spockframework</groupId>
+            <artifactId>spock-core</artifactId>
+            <version>1.1-groovy-2.4</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.codehaus.gmavenplus</groupId>
+                <artifactId>gmavenplus-plugin</artifactId>
+                <version>1.6</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>addSources</goal>
+                            <goal>addTestSources</goal>
+                            <goal>compile</goal>
+                            <goal>compileTests</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>${maven-surefire-plugin.version}</version>
+            </plugin>
+            <plugin>
+                <artifactId>maven-failsafe-plugin</artifactId>
+                <version>2.19.1</version>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.junit.platform</groupId>
+                        <artifactId>junit-platform-surefire-provider</artifactId>
+                        <version>${junit.platform.version}</version>
+                    </dependency>
+                </dependencies>
+                <executions>
+                    <execution>
+                        <id>junit5</id>
+                        <goals>
+                            <goal>integration-test</goal>
+                            <goal>verify</goal>
+                        </goals>
+                        <configuration>
+                            <includes>
+                                <include>**/*Test5.java</include>
+                            </includes>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <kotlin-maven-plugin.version>1.1.2</kotlin-maven-plugin.version>
+        <kotlin-test-junit.version>1.1.2</kotlin-test-junit.version>
+        <kotlin-stdlib.version>1.1.2</kotlin-stdlib.version>
+        <kotlin-reflect.version>1.1.2</kotlin-reflect.version>
+        <kotlinx.version>0.15</kotlinx.version>
+        <mockito-kotlin.version>1.5.0</mockito-kotlin.version>
+
+        <junit.jupiter.version>5.0.0</junit.jupiter.version>
+        <junit.platform.version>1.0.0</junit.platform.version>
+        <junit.vintage.version>4.12.0</junit.vintage.version>
+        <junit4.version>4.12</junit4.version>
+    </properties>
+</project>
+

core-groovy/src/main/groovy/com/baeldung/json/Account.groovy

@@ -0,0 +1,7 @@
+package com.baeldung.json
+
+class Account {
+    String id
+    BigDecimal value
+    Date createdAt
+}

core-groovy/src/main/groovy/com/baeldung/json/JsonParser.groovy

@@ -0,0 +1,27 @@
+package com.baeldung.json
+
+import groovy.json.JsonOutput
+import groovy.json.JsonParserType
+import groovy.json.JsonSlurper
+
+class JsonParser {
+
+    Account toObject(String json) {
+        JsonSlurper jsonSlurper = new JsonSlurper()
+        jsonSlurper.parseText(json) as Account
+    }
+
+    Account toObjectWithIndexOverlay(String json) {
+        JsonSlurper jsonSlurper = new JsonSlurper(type: JsonParserType.INDEX_OVERLAY)
+        jsonSlurper.parseText(json) as Account
+    }
+
+    String toJson(Account account) {
+        JsonOutput.toJson(account)
+    }
+
+    String prettyfy(String json) {
+        JsonOutput.prettyPrint(json)
+    }
+
+}

core-groovy/src/test/groovy/com/baeldung/groovy/sql/SqlTest.groovy

@@ -0,0 +1,229 @@
+package com.baeldung.groovy.sql
+
+import groovy.sql.GroovyResultSet
+import groovy.sql.GroovyRowResult
+import groovy.sql.Sql
+import groovy.transform.CompileStatic
+import static org.junit.Assert.*
+import org.junit.Test
+
+class SqlTest {
+
+    final Map dbConnParams = [url: 'jdbc:hsqldb:mem:testDB', user: 'sa', password: '', driver: 'org.hsqldb.jdbc.JDBCDriver']
+
+    @Test
+    void whenNewSqlInstance_thenDbIsAccessed() {
+        def sql = Sql.newInstance(dbConnParams)
+        sql.close()
+        sql.close()
+    }
+
+    @Test
+    void whenTableDoesNotExist_thenSelectFails() {
+        try {
+            Sql.withInstance(dbConnParams) { Sql sql ->
+                sql.eachRow('select * from PROJECT') {}
+            }
+
+            fail("An exception should have been thrown")
+        } catch (ignored) {
+            //Ok
+        }
+    }
+
+    @Test
+    void whenTableCreated_thenSelectIsPossible() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            def result = sql.execute 'create table PROJECT_1 (id integer not null, name varchar(50), url varchar(100))'
+
+            assertEquals(0, sql.updateCount)
+            assertFalse(result)
+
+            result = sql.execute('select * from PROJECT_1')
+
+            assertTrue(result)
+        }
+    }
+
+    @Test
+    void whenIdentityColumn_thenInsertReturnsNewId() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_2 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            def ids = sql.executeInsert("INSERT INTO PROJECT_2 (NAME, URL) VALUES ('tutorials', 'github.com/eugenp/tutorials')")
+
+            assertEquals(0, ids[0][0])
+
+            ids = sql.executeInsert("INSERT INTO PROJECT_2 (NAME, URL) VALUES ('REST with Spring', 'github.com/eugenp/REST-With-Spring')")
+
+            assertEquals(1, ids[0][0])
+        }
+    }
+
+    @Test
+    void whenUpdate_thenNumberOfAffectedRows() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_3 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            sql.executeInsert("INSERT INTO PROJECT_3 (NAME, URL) VALUES ('tutorials', 'github.com/eugenp/tutorials')")
+            sql.executeInsert("INSERT INTO PROJECT_3 (NAME, URL) VALUES ('REST with Spring', 'github.com/eugenp/REST-With-Spring')")
+            def count = sql.executeUpdate("UPDATE PROJECT_3 SET URL = 'https://' + URL")
+
+            assertEquals(2, count)
+        }
+    }
+
+    @Test
+    void whenEachRow_thenResultSetHasProperties() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_4 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            sql.executeInsert("INSERT INTO PROJECT_4 (NAME, URL) VALUES ('tutorials', 'https://github.com/eugenp/tutorials')")
+            sql.executeInsert("INSERT INTO PROJECT_4 (NAME, URL) VALUES ('REST with Spring', 'https://github.com/eugenp/REST-With-Spring')")
+
+            sql.eachRow("SELECT * FROM PROJECT_4") { GroovyResultSet rs ->
+                assertNotNull(rs.name)
+                assertNotNull(rs.url)
+                assertNotNull(rs[0])
+                assertNotNull(rs[1])
+                assertNotNull(rs[2])
+                assertEquals(rs.name, rs['name'])
+                assertEquals(rs.url, rs['url'])
+            }
+        }
+    }
+
+    @Test
+    void whenPagination_thenSubsetIsReturned() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_5 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            sql.executeInsert("INSERT INTO PROJECT_5 (NAME, URL) VALUES ('tutorials', 'github.com/eugenp/tutorials')")
+            sql.executeInsert("INSERT INTO PROJECT_5 (NAME, URL) VALUES ('REST with Spring', 'github.com/eugenp/REST-With-Spring')")
+            def rows = sql.rows('SELECT * FROM PROJECT_5 ORDER BY NAME', 1, 1)
+
+            assertEquals(1, rows.size())
+            assertEquals('REST with Spring', rows[0].name)
+        }
+    }
+
+    @Test
+    void whenParameters_thenReplacement() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_6 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            sql.execute('INSERT INTO PROJECT_6 (NAME, URL) VALUES (?, ?)', 'tutorials', 'github.com/eugenp/tutorials')
+            sql.execute("INSERT INTO PROJECT_6 (NAME, URL) VALUES (:name, :url)", [name: 'REST with Spring', url: 'github.com/eugenp/REST-With-Spring'])
+
+            def rows = sql.rows("SELECT * FROM PROJECT_6 WHERE NAME = 'tutorials'")
+
+            assertEquals(1, rows.size())
+
+            rows = sql.rows("SELECT * FROM PROJECT_6 WHERE NAME = 'REST with Spring'")
+
+            assertEquals(1, rows.size())
+        }
+    }
+
+    @Test
+    void whenParametersInGString_thenReplacement() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_7 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            sql.execute "INSERT INTO PROJECT_7 (NAME, URL) VALUES (${'tutorials'}, ${'github.com/eugenp/tutorials'})"
+            def name = 'REST with Spring'
+            def url = 'github.com/eugenp/REST-With-Spring'
+            sql.execute "INSERT INTO PROJECT_7 (NAME, URL) VALUES (${name}, ${url})"
+
+            def rows = sql.rows("SELECT * FROM PROJECT_7 WHERE NAME = 'tutorials'")
+
+            assertEquals(1, rows.size())
+
+            rows = sql.rows("SELECT * FROM PROJECT_7 WHERE NAME = 'REST with Spring'")
+
+            assertEquals(1, rows.size())
+        }
+    }
+
+    @Test
+    void whenTransactionRollback_thenNoDataInserted() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.withTransaction {
+                sql.execute 'create table PROJECT_8 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+                sql.executeInsert("INSERT INTO PROJECT_8 (NAME, URL) VALUES ('tutorials', 'https://github.com/eugenp/tutorials')")
+                sql.executeInsert("INSERT INTO PROJECT_8 (NAME, URL) VALUES ('REST with Spring', 'https://github.com/eugenp/REST-With-Spring')")
+                sql.rollback()
+
+                def rows = sql.rows("SELECT * FROM PROJECT_8")
+
+                assertEquals(0, rows.size())
+            }
+        }
+    }
+
+    @Test
+    void whenTransactionRollbackThenCommit_thenOnlyLastInserted() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.withTransaction {
+                sql.execute 'create table PROJECT_9 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+                sql.executeInsert("INSERT INTO PROJECT_9 (NAME, URL) VALUES ('tutorials', 'https://github.com/eugenp/tutorials')")
+                sql.rollback()
+                sql.executeInsert("INSERT INTO PROJECT_9 (NAME, URL) VALUES ('REST with Spring', 'https://github.com/eugenp/REST-With-Spring')")
+                sql.rollback()
+                sql.executeInsert("INSERT INTO PROJECT_9 (NAME, URL) VALUES ('tutorials', 'https://github.com/eugenp/tutorials')")
+                sql.executeInsert("INSERT INTO PROJECT_9 (NAME, URL) VALUES ('REST with Spring', 'https://github.com/eugenp/REST-With-Spring')")
+            }
+
+            def rows = sql.rows("SELECT * FROM PROJECT_9")
+
+            assertEquals(2, rows.size())
+        }
+    }
+
+    @Test
+    void whenException_thenTransactionIsRolledBack() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            try {
+                sql.withTransaction {
+                    sql.execute 'create table PROJECT_10 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+                    sql.executeInsert("INSERT INTO PROJECT_10 (NAME, URL) VALUES ('tutorials', 'https://github.com/eugenp/tutorials')")
+                    throw new Exception('rollback')
+                }
+            } catch (ignored) {}
+
+            def rows = sql.rows("SELECT * FROM PROJECT_10")
+
+            assertEquals(0, rows.size())
+        }
+    }
+
+    @Test
+    void givenCachedConnection_whenException_thenDataIsPersisted() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            try {
+                sql.cacheConnection {
+                    sql.execute 'create table PROJECT_11 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+                    sql.executeInsert("INSERT INTO PROJECT_11 (NAME, URL) VALUES ('tutorials', 'https://github.com/eugenp/tutorials')")
+                    throw new Exception('This does not rollback')
+                }
+            } catch (ignored) {}
+
+            def rows = sql.rows("SELECT * FROM PROJECT_11")
+
+            assertEquals(1, rows.size())
+        }
+    }
+
+    /*@Test
+    void whenModifyResultSet_thenDataIsChanged() {
+        Sql.withInstance(dbConnParams) { Sql sql ->
+            sql.execute 'create table PROJECT_5 (ID IDENTITY, NAME VARCHAR (50), URL VARCHAR (100))'
+            sql.executeInsert("INSERT INTO PROJECT_5 (NAME, URL) VALUES ('tutorials', 'github.com/eugenp/tutorials')")
+            sql.executeInsert("INSERT INTO PROJECT_5 (NAME, URL) VALUES ('REST with Spring', 'github.com/eugenp/REST-With-Spring')")
+
+            sql.eachRow("SELECT * FROM PROJECT_5 FOR UPDATE ") { GroovyResultSet rs ->
+                rs['name'] = "The great ${rs.name}!" as String
+                rs.updateRow()
+            }
+
+            sql.eachRow("SELECT * FROM PROJECT_5") { GroovyResultSet rs ->
+                assertTrue(rs.name.startsWith('The great '))
+            }
+        }
+    }*/
+
+}

core-groovy/src/test/groovy/com/baeldung/json/JsonParserTest.groovy

@@ -0,0 +1,66 @@
+package com.baeldung.json
+
+import spock.lang.Specification
+
+import java.text.SimpleDateFormat
+
+class JsonParserTest extends Specification {
+
+    JsonParser jsonParser
+
+    void setup () {
+        jsonParser = new JsonParser()
+    }
+
+    def 'Should parse to Account given Json String' () {
+        given:
+            def json = '{"id":"1234","value":15.6}'
+        when:
+            def account = jsonParser.toObject(json)
+        then:
+            account
+            account instanceof Account
+            account.id == '1234'
+            account.value == 15.6
+    }
+
+    def 'Should parse to Account given Json String with date property' () {
+        given:
+            def json = '{"id":"1234","value":15.6,"createdAt":"2018-01-01T00:00:00+0000"}'
+        when:
+            def account = jsonParser.toObjectWithIndexOverlay(json)
+        then:
+            account
+            account instanceof Account
+            account.id == '1234'
+            account.value == 15.6
+            println account.createdAt
+            account.createdAt == Date.parse('yyyy-MM-dd', '2018-01-01')
+    }
+
+    def 'Should parse to Json given an Account object' () {
+        given:
+            Account account = new Account(
+                    id: '123',
+                    value: 15.6,
+                    createdAt: new SimpleDateFormat('MM/dd/yyyy').parse('01/01/2018')
+            )
+        when:
+            def json = jsonParser.toJson(account)
+        then:
+            json
+            json == '{"value":15.6,"createdAt":"2018-01-01T00:00:00+0000","id":"123"}'
+    }
+
+    def 'Should prettify given a json string' () {
+        given:
+            String json = '{"value":15.6,"createdAt":"01/01/2018","id":"123456"}'
+        when:
+            def jsonPretty = jsonParser.prettyfy(json)
+        then:
+            jsonPretty
+            jsonPretty == '{\n    "value": 15.6,\n    "createdAt": "01/01/2018",\n    "id": "123456"\n}'
+    }
+
+
+}

core-java-8/README.md

@@ -40,3 +40,6 @@
 - [Efficient Word Frequency Calculator in Java](http://www.baeldung.com/java-word-frequency)
 - [Primitive Type Streams in Java 8](http://www.baeldung.com/java-8-primitive-streams)
 - [Fail-Safe Iterator vs Fail-Fast Iterator](http://www.baeldung.com/java-fail-safe-vs-fail-fast-iterator)
+- [Shuffling Collections In Java](http://www.baeldung.com/java-shuffle-collection)
+- [Java 8 StringJoiner](http://www.baeldung.com/java-string-joiner)
+- [Introduction to Spliterator in Java](http://www.baeldung.com/java-spliterator)

core-java-8/src/test/java/com/baeldung/shufflingcollections/ShufflingCollectionsUnitTest.java

@@ -0,0 +1,70 @@
+package com.baeldung.shufflingcollections;
+
+import org.junit.Test;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ShufflingCollectionsUnitTest {
+
+    @Test
+    public void whenShufflingList_thenListIsShuffled() {
+        List<String> students = Arrays.asList("Foo", "Bar", "Baz", "Qux");
+
+        System.out.println("List before shuffling:");
+        System.out.println(students);
+
+        Collections.shuffle(students);
+        System.out.println("List after shuffling:");
+        System.out.println(students);
+    }
+
+    @Test
+    public void whenShufflingMapEntries_thenValuesAreShuffled() {
+        Map<Integer, String> studentsById = new HashMap<>();
+        studentsById.put(1, "Foo");
+        studentsById.put(2, "Bar");
+        studentsById.put(3, "Baz");
+        studentsById.put(4, "Qux");
+
+        System.out.println("Students before shuffling:");
+        System.out.println(studentsById.values());
+
+        List<Map.Entry<Integer, String>> shuffledStudentEntries = new ArrayList<>(studentsById.entrySet());
+        Collections.shuffle(shuffledStudentEntries);
+
+        List<String> shuffledStudents = shuffledStudentEntries.stream()
+                .map(Map.Entry::getValue)
+                .collect(Collectors.toList());
+
+        System.out.println("Students after shuffling");
+        System.out.println(shuffledStudents);
+    }
+
+    @Test
+    public void whenShufflingSet_thenElementsAreShuffled() {
+        Set<String> students = new HashSet<>(Arrays.asList("Foo", "Bar", "Baz", "Qux"));
+
+        System.out.println("Set before shuffling:");
+        System.out.println(students);
+
+        List<String> studentList = new ArrayList<>(students);
+
+        Collections.shuffle(studentList);
+        System.out.println("Shuffled set elements:");
+        System.out.println(studentList);
+    }
+
+    @Test
+    public void whenShufflingWithSameRandomness_thenElementsAreShuffledDeterministically() {
+        List<String> students_1 = Arrays.asList("Foo", "Bar", "Baz", "Qux");
+        List<String> students_2 = Arrays.asList("Foo", "Bar", "Baz", "Qux");
+
+        Collections.shuffle(students_1, new Random(5));
+        Collections.shuffle(students_2, new Random(5));
+
+        assertThat(students_1).isEqualTo(students_2);
+    }
+}

core-java-9/src/main/java/com/baeldung/java9/methodhandles/Book.java

@@ -0,0 +1,17 @@
+package com.baeldung.java9.methodhandles;
+
+public class Book {
+
+    String id;
+    String title;
+
+    public Book(String id, String title) {
+        this.id = id;
+        this.title = title;
+    }
+
+    @SuppressWarnings("unused")
+    private String formatBook() {
+        return id + " > " + title;
+    }
+}

core-java-9/src/test/java/com/baeldung/java9/methodhandles/MethodHandlesTest.java

@@ -0,0 +1,152 @@
+package com.baeldung.java9.methodhandles;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.*;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.lang.invoke.WrongMethodTypeException;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+/**
+ * Test case for the {@link MethodHandles} API
+ */
+public class MethodHandlesTest {
+
+    @Test
+    public void givenConcatMethodHandle_whenInvoked_thenCorrectlyConcatenated() throws Throwable {
+
+        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
+        MethodType mt = MethodType.methodType(String.class, String.class);
+        MethodHandle concatMH = publicLookup.findVirtual(String.class, "concat", mt);
+
+        String output = (String) concatMH.invoke("Effective ", "Java");
+
+        assertEquals("Effective Java", output);
+    }
+
+    @Test
+    public void givenAsListMethodHandle_whenInvokingWithArguments_thenCorrectlyInvoked() throws Throwable {
+        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
+        MethodType mt = MethodType.methodType(List.class, Object[].class);
+        MethodHandle asListMH = publicLookup.findStatic(Arrays.class, "asList", mt);
+
+        List<Integer> list = (List<Integer>) asListMH.invokeWithArguments(1, 2);
+
+        assertThat(Arrays.asList(1, 2), is(list));
+    }
+
+    @Test
+    public void givenConstructorMethodHandle_whenInvoked_thenObjectCreatedCorrectly() throws Throwable {
+        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
+        MethodType mt = MethodType.methodType(void.class, String.class);
+        MethodHandle newIntegerMH = publicLookup.findConstructor(Integer.class, mt);
+
+        Integer integer = (Integer) newIntegerMH.invoke("1");
+
+        assertEquals(1, integer.intValue());
+    }
+
+    @Test
+    public void givenAFieldWithoutGetter_whenCreatingAGetter_thenCorrectlyInvoked() throws Throwable {
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        MethodHandle getTitleMH = lookup.findGetter(Book.class, "title", String.class);
+
+        Book book = new Book("ISBN-1234", "Effective Java");
+
+        assertEquals("Effective Java", getTitleMH.invoke(book));
+    }
+
+    @Test
+    public void givenPrivateMethod_whenCreatingItsMethodHandle_thenCorrectlyInvoked() throws Throwable {
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        Method formatBookMethod = Book.class.getDeclaredMethod("formatBook");
+        formatBookMethod.setAccessible(true);
+
+        MethodHandle formatBookMH = lookup.unreflect(formatBookMethod);
+
+        Book book = new Book("ISBN-123", "Java in Action");
+
+        assertEquals("ISBN-123 > Java in Action", formatBookMH.invoke(book));
+    }
+
+    @Test
+    public void givenReplaceMethod_whenUsingReflectionAndInvoked_thenCorrectlyReplaced() throws Throwable {
+        Method replaceMethod = String.class.getMethod("replace", char.class, char.class);
+
+        String string = (String) replaceMethod.invoke("jovo", 'o', 'a');
+
+        assertEquals("java", string);
+    }
+
+    @Test
+    public void givenReplaceMethodHandle_whenInvoked_thenCorrectlyReplaced() throws Throwable {
+        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
+        MethodType mt = MethodType.methodType(String.class, char.class, char.class);
+        MethodHandle replaceMH = publicLookup.findVirtual(String.class, "replace", mt);
+
+        String replacedString = (String) replaceMH.invoke("jovo", Character.valueOf('o'), 'a');
+
+        assertEquals("java", replacedString);
+    }
+
+    @Test
+    public void givenReplaceMethodHandle_whenInvokingExact_thenCorrectlyReplaced() throws Throwable {
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        MethodType mt = MethodType.methodType(String.class, char.class, char.class);
+        MethodHandle replaceMH = lookup.findVirtual(String.class, "replace", mt);
+
+        String s = (String) replaceMH.invokeExact("jovo", 'o', 'a');
+
+        assertEquals("java", s);
+    }
+
+    @Test
+    public void givenSumMethodHandle_whenInvokingExact_thenSumIsCorrect() throws Throwable {
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        MethodType mt = MethodType.methodType(int.class, int.class, int.class);
+        MethodHandle sumMH = lookup.findStatic(Integer.class, "sum", mt);
+
+        int sum = (int) sumMH.invokeExact(1, 11);
+
+        assertEquals(12, sum);
+    }
+
+    @Test(expected = WrongMethodTypeException.class)
+    public void givenSumMethodHandleAndIncompatibleArguments_whenInvokingExact_thenException() throws Throwable {
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        MethodType mt = MethodType.methodType(int.class, int.class, int.class);
+        MethodHandle sumMH = lookup.findStatic(Integer.class, "sum", mt);
+
+        sumMH.invokeExact(Integer.valueOf(1), 11);
+    }
+
+    @Test
+    public void givenSpreadedEqualsMethodHandle_whenInvokedOnArray_thenCorrectlyEvaluated() throws Throwable {
+        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
+        MethodType mt = MethodType.methodType(boolean.class, Object.class);
+        MethodHandle equalsMH = publicLookup.findVirtual(String.class, "equals", mt);
+
+        MethodHandle methodHandle = equalsMH.asSpreader(Object[].class, 2);
+
+        assertTrue((boolean) methodHandle.invoke(new Object[] { "java", "java" }));
+        assertFalse((boolean) methodHandle.invoke(new Object[] { "java", "jova" }));
+    }
+
+    @Test
+    public void givenConcatMethodHandle_whenBindToAString_thenCorrectlyConcatenated() throws Throwable {
+        MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
+        MethodType mt = MethodType.methodType(String.class, String.class);
+        MethodHandle concatMH = publicLookup.findVirtual(String.class, "concat", mt);
+
+        MethodHandle bindedConcatMH = concatMH.bindTo("Hello ");
+
+        assertEquals("Hello World!", bindedConcatMH.invoke("World!"));
+    }
+}

core-java-concurrency/src/test/java/com/baeldung/concurrent/stopping/StopThreadManualTest.java

@@ -10,7 +10,7 @@ import org.junit.Test;
 
 import com.jayway.awaitility.Awaitility;
 
-public class StopThreadTest {
+public class StopThreadManualTest {
 
     @Test
     public void whenStoppedThreadIsStopped() throws InterruptedException {

core-java-io/.gitignore

@@ -1,26 +1,5 @@
-*.class
-
 0.*
 
-#folders#
-/target
-/neoDb*
-/data
-/src/main/webapp/WEB-INF/classes
-*/META-INF/*
-.resourceCache
-
-# Packaged files #
-*.jar
-*.war
-*.ear
-
 # Files generated by integration tests
-*.txt
+# *.txt
-backup-pom.xml
-/bin/
 /temp
-
-#IntelliJ specific
-.idea/
-*.iml

core-java-io/pom.xml

@@ -1,5 +1,4 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.baeldung</groupId>
     <artifactId>core-java-io</artifactId>
@@ -211,16 +210,6 @@
             <artifactId>jmh-generator-annprocess</artifactId>
             <version>1.19</version>
         </dependency>
-		<dependency>
-		    <groupId>org.springframework</groupId>
-		    <artifactId>spring-web</artifactId>
-		    <version>4.3.4.RELEASE</version>
-		</dependency>
- 		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter</artifactId>
-			<version>1.5.8.RELEASE</version>
-		</dependency>
         <dependency>
             <groupId>org.hsqldb</groupId>
             <artifactId>hsqldb</artifactId>
@@ -264,99 +253,6 @@
                 </configuration>
             </plugin>
 
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-dependency-plugin</artifactId>
-                <executions>
-                    <execution>
-                        <id>copy-dependencies</id>
-                        <phase>prepare-package</phase>
-                        <goals>
-                            <goal>copy-dependencies</goal>
-                        </goals>
-                        <configuration>
-                            <outputDirectory>${project.build.directory}/libs</outputDirectory>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
-
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-jar-plugin</artifactId>
-                <configuration>
-                    <archive>
-                        <manifest>
-                            <addClasspath>true</addClasspath>
-                            <classpathPrefix>libs/</classpathPrefix>
-                            <mainClass>org.baeldung.executable.ExecutableMavenJar</mainClass>
-                        </manifest>
-                    </archive>
-                </configuration>
-            </plugin>
-
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-assembly-plugin</artifactId>
-                <executions>
-                    <execution>
-                        <phase>package</phase>
-                        <goals>
-                            <goal>single</goal>
-                        </goals>
-                        <configuration>
-                            <archiveBaseDirectory>${project.basedir}</archiveBaseDirectory>
-                            <archive>
-                                <manifest>
-                                    <mainClass>org.baeldung.executable.ExecutableMavenJar</mainClass>
-                                </manifest>
-                            </archive>
-                            <descriptorRefs>
-                                <descriptorRef>jar-with-dependencies</descriptorRef>
-                            </descriptorRefs>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
-
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-shade-plugin</artifactId>
-                <executions>
-                    <execution>
-                        <goals>
-                            <goal>shade</goal>
-                        </goals>
-                        <configuration>
-                            <shadedArtifactAttached>true</shadedArtifactAttached>
-                            <transformers>
-                                <transformer
-                                        implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
-                                    <mainClass>org.baeldung.executable.ExecutableMavenJar</mainClass>
-                                </transformer>
-                            </transformers>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
-
-            <plugin>
-                <groupId>com.jolira</groupId>
-                <artifactId>onejar-maven-plugin</artifactId>
-                <executions>
-                    <execution>
-                        <configuration>
-                            <mainClass>org.baeldung.executable.ExecutableMavenJar</mainClass>
-                            <attachToBuild>true</attachToBuild>
-                            <filename>${project.build.finalName}-onejar.${project.packaging}</filename>
-                        </configuration>
-                        <goals>
-                            <goal>one-jar</goal>
-                        </goals>
-                    </execution>
-                </executions>
-            </plugin>
-
             <plugin>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
@@ -384,7 +280,7 @@
                         <argument>-Xmx300m</argument>
                         <argument>-XX:+UseParallelGC</argument>
                         <argument>-classpath</argument>
-                        <classpath/>
+                        <classpath />
                         <argument>com.baeldung.outofmemoryerror.OutOfMemoryGCLimitExceed</argument>
                     </arguments>
                 </configuration>
@@ -442,7 +338,7 @@
                         <executions>
                             <execution>
                                 <id>run-benchmarks</id>
-                            <!--    <phase>integration-test</phase>-->
+                                <!-- <phase>integration-test</phase> -->
                                 <phase>none</phase>
                                 <goals>
                                     <goal>exec</goal>
@@ -452,7 +348,7 @@
                                     <executable>java</executable>
                                     <arguments>
                                         <argument>-classpath</argument>
-                                        <classpath/>
+                                        <classpath />
                                         <argument>org.openjdk.jmh.Main</argument>
                                         <argument>.*</argument>
                                     </arguments>

core-java-io/src/main/resources/targetFile.tmp

@@ -1,2 +0,0 @@
-line 1
-a second line

core-java-io/src/test/java/com/baeldung/copyfiles/FileCopierTest.java

@@ -30,8 +30,7 @@ public class FileCopierTest {
     @Test
     public void givenIoAPI_whenCopied_thenCopyExistsWithSameContents() throws IOException {
         File copied = new File("src/test/resources/copiedWithIo.txt");
-		try (InputStream in = new BufferedInputStream(new FileInputStream(original));
+        try (InputStream in = new BufferedInputStream(new FileInputStream(original)); OutputStream out = new BufferedOutputStream(new FileOutputStream(copied))) {
-				OutputStream out = new BufferedOutputStream(new FileOutputStream(copied))) {
             byte[] buffer = new byte[1024];
             int lengthRead;
             while ((lengthRead = in.read(buffer)) > 0) {

core-java-io/src/test/java/com/baeldung/file/FileOperationsManualTest.java

@@ -3,7 +3,6 @@ package com.baeldung.file;
 import org.apache.commons.io.FileUtils;
 import org.hamcrest.CoreMatchers;
 import org.hamcrest.Matchers;
-import org.junit.Assert;
 import org.junit.Test;
 
 import java.io.BufferedReader;

core-java-io/src/test/java/com/baeldung/file/FilesTest.java

@@ -42,19 +42,14 @@ public class FilesTest {
         CharSink chs = com.google.common.io.Files.asCharSink(file, Charsets.UTF_8, FileWriteMode.APPEND);
         chs.write("Spain\r\n");
 
-        assertThat(StreamUtils.getStringFromInputStream(
+        assertThat(StreamUtils.getStringFromInputStream(new FileInputStream(fileName))).isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
-          new FileInputStream(fileName)))
-          .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
     }
 
-
     @Test
     public void whenAppendToFileUsingFiles_thenCorrect() throws IOException {
         Files.write(Paths.get(fileName), "Spain\r\n".getBytes(), StandardOpenOption.APPEND);
 
-        assertThat(StreamUtils.getStringFromInputStream(
+        assertThat(StreamUtils.getStringFromInputStream(new FileInputStream(fileName))).isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
-          new FileInputStream(fileName)))
-          .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
     }
 
     @Test
@@ -62,9 +57,7 @@ public class FilesTest {
         File file = new File(fileName);
         FileUtils.writeStringToFile(file, "Spain\r\n", StandardCharsets.UTF_8, true);
 
-        assertThat(StreamUtils.getStringFromInputStream(
+        assertThat(StreamUtils.getStringFromInputStream(new FileInputStream(fileName))).isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
-          new FileInputStream(fileName)))
-          .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
     }
 
     @Test
@@ -73,9 +66,7 @@ public class FilesTest {
         fos.write("Spain\r\n".getBytes());
         fos.close();
 
-        assertThat(StreamUtils.getStringFromInputStream(
+        assertThat(StreamUtils.getStringFromInputStream(new FileInputStream(fileName))).isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
-          new FileInputStream(fileName)))
-          .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
     }
 
     @Test
@@ -86,9 +77,6 @@ public class FilesTest {
         bw.newLine();
         bw.close();
 
-        assertThat(
+        assertThat(StreamUtils.getStringFromInputStream(new FileInputStream(fileName))).isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\n");
-          StreamUtils.getStringFromInputStream(
-            new FileInputStream(fileName)))
-          .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\n");
     }
 }

core-java-io/src/test/java/com/baeldung/java/nio2/PathManualTest.java

@@ -9,7 +9,6 @@ import java.net.URI;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.util.Date;
 
 import org.junit.Test;
 

core-java-io/src/test/java/com/baeldung/java/nio2/async/AsyncFileIntegrationTest.java

@@ -17,18 +17,19 @@ import java.util.concurrent.Future;
 import static org.junit.Assert.assertEquals;
 
 public class AsyncFileIntegrationTest {
+
     @Test
     public void givenPath_whenReadsContentWithFuture_thenCorrect() throws IOException, ExecutionException, InterruptedException {
-        Path path = Paths.get(URI.create(this.getClass().getClassLoader().getResource("file.txt").toString()));
+        final Path path = Paths.get(URI.create(this.getClass().getClassLoader().getResource("file.txt").toString()));
-        AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
+        final AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
 
-        ByteBuffer buffer = ByteBuffer.allocate(1024);
+        final ByteBuffer buffer = ByteBuffer.allocate(1024);
 
-        Future<Integer> operation = fileChannel.read(buffer, 0);
+        final Future<Integer> operation = fileChannel.read(buffer, 0);
 
         operation.get();
 
-        String fileContent = new String(buffer.array()).trim();
+        final String fileContent = new String(buffer.array()).trim();
         buffer.clear();
 
         assertEquals(fileContent, "baeldung.com");
@@ -36,18 +37,16 @@ public class AsyncFileIntegrationTest {
 
     @Test
     public void givenPath_whenReadsContentWithCompletionHandler_thenCorrect() throws IOException {
-        Path path = Paths.get(URI.create(AsyncFileIntegrationTest.class.getResource("/file.txt").toString()));
+        final Path path = Paths.get(URI.create(this.getClass().getClassLoader().getResource("file.txt").toString()));
-        AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
+        final AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
 
-        ByteBuffer buffer = ByteBuffer.allocate(1024);
+        final ByteBuffer buffer = ByteBuffer.allocate(1024);
 
         fileChannel.read(buffer, 0, buffer, new CompletionHandler<Integer, ByteBuffer>() {
-
             @Override
             public void completed(Integer result, ByteBuffer attachment) {
                 // result is number of bytes read
                 // attachment is the buffer
-
             }
 
             @Override
@@ -59,42 +58,40 @@ public class AsyncFileIntegrationTest {
 
     @Test
     public void givenPathAndContent_whenWritesToFileWithFuture_thenCorrect() throws IOException, ExecutionException, InterruptedException {
-        String fileName = "temp";
+        final String fileName = "temp";
-        Path path = Paths.get(fileName);
+        final Path path = Paths.get(fileName);
-        AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE, StandardOpenOption.CREATE);
+        final AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE, StandardOpenOption.CREATE);
 
-        ByteBuffer buffer = ByteBuffer.allocate(1024);
+        final ByteBuffer buffer = ByteBuffer.allocate(1024);
-        long position = 0;
+        final long position = 0;
 
         buffer.put("hello world".getBytes());
         buffer.flip();
 
-        Future<Integer> operation = fileChannel.write(buffer, position);
+        final Future<Integer> operation = fileChannel.write(buffer, position);
         buffer.clear();
 
         operation.get();
 
-        String content = readContent(path);
+        final String content = readContent(path);
         assertEquals("hello world", content);
     }
 
     @Test
     public void givenPathAndContent_whenWritesToFileWithHandler_thenCorrect() throws IOException {
-        String fileName = UUID.randomUUID().toString();
+        final String fileName = UUID.randomUUID().toString();
-        Path path = Paths.get(fileName);
+        final Path path = Paths.get(fileName);
-        AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.DELETE_ON_CLOSE);
+        final AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.DELETE_ON_CLOSE);
 
-        ByteBuffer buffer = ByteBuffer.allocate(1024);
+        final ByteBuffer buffer = ByteBuffer.allocate(1024);
         buffer.put("hello world".getBytes());
         buffer.flip();
 
         fileChannel.write(buffer, 0, buffer, new CompletionHandler<Integer, ByteBuffer>() {
-
             @Override
             public void completed(Integer result, ByteBuffer attachment) {
                 // result is number of bytes written
                 // attachment is the buffer
-
             }
 
             @Override
@@ -104,23 +101,25 @@ public class AsyncFileIntegrationTest {
         });
     }
 
-    public static String readContent(Path file) throws ExecutionException, InterruptedException {
+    //
+
+    private String readContent(Path file) throws ExecutionException, InterruptedException {
         AsynchronousFileChannel fileChannel = null;
         try {
             fileChannel = AsynchronousFileChannel.open(file, StandardOpenOption.READ);
         } catch (IOException e) {
-            // TODO Auto-generated catch block
             e.printStackTrace();
         }
 
-        ByteBuffer buffer = ByteBuffer.allocate(1024);
+        final ByteBuffer buffer = ByteBuffer.allocate(1024);
 
-        Future<Integer> operation = fileChannel.read(buffer, 0);
+        final Future<Integer> operation = fileChannel.read(buffer, 0);
 
         operation.get();
 
-        String fileContent = new String(buffer.array()).trim();
+        final String fileContent = new String(buffer.array()).trim();
         buffer.clear();
         return fileContent;
     }
+
 }

core-java-io/src/test/java/com/baeldung/java/nio2/attributes/BasicAttribsIntegrationTest.java

@@ -20,7 +20,6 @@ public class BasicAttribsIntegrationTest {
 
     private static final Logger LOG = LoggerFactory.getLogger(BasicAttribsIntegrationTest.class);
 
-
     private static final String HOME = System.getProperty("user.home");
     private static BasicFileAttributes basicAttribs;
 

core-java-io/src/test/java/com/baeldung/java8/JavaFolderSizeUnitTest.java

@@ -55,12 +55,7 @@ public class JavaFolderSizeUnitTest {
     @Test
     public void whenGetFolderSizeUsingJava8_thenCorrect() throws IOException {
         final Path folder = Paths.get(path);
-        final long size = Files.walk(folder)
+        final long size = Files.walk(folder).filter(p -> p.toFile().isFile()).mapToLong(p -> p.toFile().length()).sum();
-            .filter(p -> p.toFile()
-                .isFile())
-            .mapToLong(p -> p.toFile()
-                .length())
-            .sum();
 
         assertEquals(EXPECTED_SIZE, size);
     }
@@ -77,12 +72,8 @@ public class JavaFolderSizeUnitTest {
     public void whenGetFolderSizeUsingGuava_thenCorrect() {
         final File folder = new File(path);
 
-        final Iterable<File> files = com.google.common.io.Files.fileTreeTraverser()
+        final Iterable<File> files = com.google.common.io.Files.fileTreeTraverser().breadthFirstTraversal(folder);
-            .breadthFirstTraversal(folder);
+        final long size = StreamSupport.stream(files.spliterator(), false).filter(File::isFile).mapToLong(File::length).sum();
-        final long size = StreamSupport.stream(files.spliterator(), false)
-            .filter(File::isFile)
-            .mapToLong(File::length)
-            .sum();
 
         assertEquals(EXPECTED_SIZE, size);
     }

core-java-io/src/test/java/com/baeldung/mappedbytebuffer/MappedByteBufferUnitTest.java

@@ -18,14 +18,13 @@ import static org.junit.Assert.assertNotNull;
 
 public class MappedByteBufferUnitTest {
 
-
     @Test
     public void givenFileChannel_whenReadToTheMappedByteBuffer_thenShouldSuccess() throws Exception {
-        //given
+        // given
         CharBuffer charBuffer = null;
         Path pathToRead = getFileURIFromResources("fileToRead.txt");
 
-        //when
+        // when
         try (FileChannel fileChannel = (FileChannel) Files.newByteChannel(pathToRead, EnumSet.of(StandardOpenOption.READ))) {
             MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, fileChannel.size());
 
@@ -34,20 +33,19 @@ public class MappedByteBufferUnitTest {
             }
         }
 
-        //then
+        // then
         assertNotNull(charBuffer);
         assertEquals(charBuffer.toString(), "This is a content of the file");
     }
 
     @Test
     public void givenPath_whenWriteToItUsingMappedByteBuffer_thenShouldSuccessfullyWrite() throws Exception {
-        //given
+        // given
-        CharBuffer charBuffer = CharBuffer.wrap("This will be written to the file");
+        final CharBuffer charBuffer = CharBuffer.wrap("This will be written to the file");
-        Path pathToWrite = getFileURIFromResources("fileToWriteTo.txt");
+        final Path pathToWrite = getFileURIFromResources("fileToWriteTo.txt");
 
-        //when
+        // when
-        try (FileChannel fileChannel = (FileChannel) Files.newByteChannel(pathToWrite,
+        try (FileChannel fileChannel = (FileChannel) Files.newByteChannel(pathToWrite, EnumSet.of(StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING))) {
-          EnumSet.of(StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING))) {
             MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, charBuffer.length());
 
             if (mappedByteBuffer != null) {
@@ -55,14 +53,16 @@ public class MappedByteBufferUnitTest {
             }
         }
 
-        //then
+        // then
-        List<String> fileContent = Files.readAllLines(pathToWrite);
+        final List<String> fileContent = Files.readAllLines(pathToWrite);
         assertEquals(fileContent.get(0), "This will be written to the file");
 
     }
 
-    private Path getFileURIFromResources(String fileName) throws Exception {
+    //
-        ClassLoader classLoader = getClass().getClassLoader();
+
+    private final Path getFileURIFromResources(String fileName) throws Exception {
+        final ClassLoader classLoader = getClass().getClassLoader();
         return Paths.get(classLoader.getResource(fileName).toURI());
     }
 }

core-java-io/src/test/java/com/baeldung/stream/FileCopyTest.java

@@ -1,47 +0,0 @@
-package com.baeldung.stream;
-
-import static org.junit.Assert.assertTrue;
-
-import java.io.File;
-import java.io.IOException;
-
-import org.junit.Test;
-
-public class FileCopyTest {
-
-    @Test
-    public void whenUsingStream_thenCopyFile() throws IOException {
-        File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_stream.txt");
-        File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_stream.txt");
-        FileCopy.copyFileUsingStream(src, dest);
-        assertTrue(dest.exists());
-        dest.delete();
-    }
-
-    @Test
-    public void whenUsingFiles_thenCopyFile() throws IOException {
-        File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_files.txt");
-        File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_files.txt");
-        FileCopy.copyFileUsingJavaFiles(src, dest);
-        assertTrue(dest.exists());
-        dest.delete();
-    }
-
-    @Test
-    public void whenUsingChannel_thenCopyFile() throws IOException {
-        File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_channel.txt");
-        File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_channel.txt");
-        FileCopy.copyFileUsingChannel(src, dest);
-        assertTrue(dest.exists());
-        dest.delete();
-    }
-
-    @Test
-    public void whenUsingApache_thenCopyFile() throws IOException {
-        File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_apache.txt");
-        File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_apache.txt");
-        FileCopy.copyFileUsingApacheCommonsIO(src, dest);
-        assertTrue(dest.exists());
-        dest.delete();
-    }
-}

core-java-io/src/test/java/com/baeldung/stream/FileCopyUnitTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.stream;
+
+import static org.junit.Assert.assertTrue;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.junit.Test;
+
+public class FileCopyUnitTest {
+
+    @Test
+    public void whenUsingStream_thenCopyFile() throws IOException {
+        final File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_stream.txt");
+        final File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_stream.txt");
+        FileCopy.copyFileUsingStream(src, dest);
+
+        assertTrue(dest.exists());
+        dest.delete();
+    }
+
+    @Test
+    public void whenUsingFiles_thenCopyFile() throws IOException {
+        final File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_files.txt");
+        final File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_files.txt");
+        FileCopy.copyFileUsingJavaFiles(src, dest);
+
+        assertTrue(dest.exists());
+        dest.delete();
+    }
+
+    @Test
+    public void whenUsingChannel_thenCopyFile() throws IOException {
+        final File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_channel.txt");
+        final File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_channel.txt");
+        FileCopy.copyFileUsingChannel(src, dest);
+
+        assertTrue(dest.exists());
+        dest.delete();
+    }
+
+    @Test
+    public void whenUsingApache_thenCopyFile() throws IOException {
+        final File src = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "src" + File.separator + "test_apache.txt");
+        final File dest = new File("src" + File.separator + "test" + File.separator + "resources" + File.separator + "copyTest" + File.separator + "dest" + File.separator + "test_apache.txt");
+        FileCopy.copyFileUsingApacheCommonsIO(src, dest);
+
+        assertTrue(dest.exists());
+        dest.delete();
+    }
+
+}

core-java-io/src/test/java/org/baeldung/java/io/JavaInputStreamToXUnitTest.java

@@ -152,11 +152,11 @@ public class JavaInputStreamToXUnitTest {
 
     @Test
     public final void whenConvertingToFile_thenCorrect() throws IOException {
-        final InputStream initialStream = new FileInputStream(new File("src/main/resources/sample.txt"));
+        final InputStream initialStream = new FileInputStream(new File("src/test/resources/sample.txt"));
         final byte[] buffer = new byte[initialStream.available()];
         initialStream.read(buffer);
 
-        final File targetFile = new File("src/main/resources/targetFile.tmp");
+        final File targetFile = new File("src/test/resources/targetFile.tmp");
         final OutputStream outStream = new FileOutputStream(targetFile);
         outStream.write(buffer);
 
@@ -166,8 +166,8 @@ public class JavaInputStreamToXUnitTest {
 
     @Test
     public final void whenConvertingInProgressToFile_thenCorrect() throws IOException {
-        final InputStream initialStream = new FileInputStream(new File("src/main/resources/sample.txt"));
+        final InputStream initialStream = new FileInputStream(new File("src/test/resources/sample.txt"));
-        final File targetFile = new File("src/main/resources/targetFile.tmp");
+        final File targetFile = new File("src/test/resources/targetFile.tmp");
         final OutputStream outStream = new FileOutputStream(targetFile);
 
         final byte[] buffer = new byte[8 * 1024];
@@ -182,8 +182,8 @@ public class JavaInputStreamToXUnitTest {
 
     @Test
     public final void whenConvertingAnInProgressInputStreamToFile_thenCorrect2() throws IOException {
-        final InputStream initialStream = new FileInputStream(new File("src/main/resources/sample.txt"));
+        final InputStream initialStream = new FileInputStream(new File("src/test/resources/sample.txt"));
-        final File targetFile = new File("src/main/resources/targetFile.tmp");
+        final File targetFile = new File("src/test/resources/targetFile.tmp");
 
         java.nio.file.Files.copy(initialStream, targetFile.toPath(), StandardCopyOption.REPLACE_EXISTING);
 
@@ -192,11 +192,11 @@ public class JavaInputStreamToXUnitTest {
 
     @Test
     public final void whenConvertingInputStreamToFile_thenCorrect3() throws IOException {
-        final InputStream initialStream = new FileInputStream(new File("src/main/resources/sample.txt"));
+        final InputStream initialStream = new FileInputStream(new File("src/test/resources/sample.txt"));
         final byte[] buffer = new byte[initialStream.available()];
         initialStream.read(buffer);
 
-        final File targetFile = new File("src/main/resources/targetFile.tmp");
+        final File targetFile = new File("src/test/resources/targetFile.tmp");
         Files.write(buffer, targetFile);
 
         IOUtils.closeQuietly(initialStream);
@@ -204,9 +204,9 @@ public class JavaInputStreamToXUnitTest {
 
     @Test
     public final void whenConvertingInputStreamToFile_thenCorrect4() throws IOException {
-        final InputStream initialStream = FileUtils.openInputStream(new File("src/main/resources/sample.txt"));
+        final InputStream initialStream = FileUtils.openInputStream(new File("src/test/resources/sample.txt"));
 
-        final File targetFile = new File("src/main/resources/targetFile.tmp");
+        final File targetFile = new File("src/test/resources/targetFile.tmp");
 
         FileUtils.copyInputStreamToFile(initialStream, targetFile);
     }

core-java-io/src/test/java/org/baeldung/java/io/JavaReadFromFileUnitTest.java

@@ -18,7 +18,6 @@ import static org.junit.Assert.assertTrue;
 
 public class JavaReadFromFileUnitTest {
 
-
     private static final Logger LOG = LoggerFactory.getLogger(JavaReadFromFileUnitTest.class);
 
     @Test
@@ -107,11 +106,12 @@ public class JavaReadFromFileUnitTest {
 
     @Test
     public void whenReadUTFEncodedFile_thenCorrect() throws IOException {
-        final String expected_value = "青空";
+        final String expected_value = "é<EFBFBD>’空";
         final BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream("src/test/resources/test_read7.in"), "UTF-8"));
         final String currentLine = reader.readLine();
         reader.close();
         LOG.debug(currentLine);
+        
         assertEquals(expected_value, currentLine);
     }
 

core-java-io/src/test/java/org/baeldung/java/io/JavaXToInputStreamUnitTest.java

@@ -68,7 +68,7 @@ public class JavaXToInputStreamUnitTest {
 
     @Test
     public final void givenUsingPlainJava_whenConvertingFileToInputStream_thenCorrect() throws IOException {
-        final File initialFile = new File("src/main/resources/sample.txt");
+        final File initialFile = new File("src/test/resources/sample.txt");
         final InputStream targetStream = new FileInputStream(initialFile);
 
         IOUtils.closeQuietly(targetStream);
@@ -76,7 +76,7 @@ public class JavaXToInputStreamUnitTest {
 
     @Test
     public final void givenUsingGuava_whenConvertingFileToInputStream_thenCorrect() throws IOException {
-        final File initialFile = new File("src/main/resources/sample.txt");
+        final File initialFile = new File("src/test/resources/sample.txt");
         final InputStream targetStream = Files.asByteSource(initialFile).openStream();
 
         IOUtils.closeQuietly(targetStream);
@@ -84,7 +84,7 @@ public class JavaXToInputStreamUnitTest {
 
     @Test
     public final void givenUsingCommonsIO_whenConvertingFileToInputStream_thenCorrect() throws IOException {
-        final File initialFile = new File("src/main/resources/sample.txt");
+        final File initialFile = new File("src/test/resources/sample.txt");
         final InputStream targetStream = FileUtils.openInputStream(initialFile);
 
         IOUtils.closeQuietly(targetStream);

core-java-io/src/test/resources/initialFile.txt

@@ -0,0 +1 @@
+With Commons IO

core-java-io/src/test/resources/sample.txt

@@ -0,0 +1 @@
+Hello World

core-java-io/src/test/resources/targetFile.tmp

@@ -0,0 +1 @@
+Hello World

core-java-io/src/test/resources/targetFile.txt

@@ -0,0 +1 @@
+Some textSome text

core-java-io/src/test/resources/test_write.txt

@@ -0,0 +1 @@
+Some StringProduct name is iPhone and its price is 1000 $

core-java-io/src/test/resources/test_write_3.txt

@@ -0,0 +1 @@
+Hello World

core-java-io/src/test/resources/test_write_5.txt

@@ -0,0 +1 @@
+Hello

core-java/README.md

@@ -127,3 +127,13 @@
 - [Polymorphism in Java](http://www.baeldung.com/java-polymorphism)
 - [Recursion In Java](http://www.baeldung.com/java-recursion)
 - [A Guide to the finalize Method in Java](http://www.baeldung.com/java-finalize)
+- [Compiling Java *.class Files with javac](http://www.baeldung.com/javac)
+- [Method Overloading and Overriding in Java](http://www.baeldung.com/java-method-overload-override)
+- [A Guide to TreeSet in Java](http://www.baeldung.com/java-tree-set)
+- [Guide to ThreadLocalRandom in Java](http://www.baeldung.com/java-thread-local-random)
+- [Java TreeMap vs HashMap](http://www.baeldung.com/java-treemap-vs-hashmap)
+- [A Guide to Iterator in Java](http://www.baeldung.com/java-iterator)
+- [The Trie Data Structure in Java](http://www.baeldung.com/trie-java)
+- [Introduction to Javadoc](http://www.baeldung.com/javadoc)
+- [How to TDD a List Implementation](http://jira.baeldung.com/browse/BAEL-1537)
+

core-java/pom.xml

@@ -78,6 +78,11 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>${gson.version}</version>
+        </dependency>
 
         <!-- logging -->
         <dependency>
@@ -468,6 +473,7 @@
     <properties>
         <!-- marshalling -->
         <jackson.version>2.8.5</jackson.version>
+        <gson.version>2.8.2</gson.version>
 
         <!-- logging -->
         <org.slf4j.version>1.7.21</org.slf4j.version>

core-java/src/main/java/com/baeldung/array/Find2ndLargestInArray.java

@@ -0,0 +1,20 @@
+package com.baeldung.array;
+
+public class Find2ndLargestInArray {
+
+    public static int find2ndLargestElement(int[] array) {
+        int maxElement = array[0];
+        int secondLargestElement = -1;
+
+        for (int index = 0; index < array.length; index++) {
+            if (maxElement <= array[index]) {
+                secondLargestElement = maxElement;
+                maxElement = array[index];
+            } else if (secondLargestElement < array[index]) {
+                secondLargestElement = array[index];
+            }
+        }
+        return secondLargestElement;
+    }
+
+}

core-java/src/main/java/com/baeldung/array/FindElementInArray.java

@@ -0,0 +1,22 @@
+package com.baeldung.array;
+
+import java.util.Arrays;
+
+public class FindElementInArray {
+
+    public static boolean findGivenElementInArrayWithoutUsingStream(int[] array, int element) {
+        boolean actualResult = false;
+
+        for (int index = 0; index < array.length; index++) {
+            if (element == array[index]) {
+                actualResult = true;
+                break;
+            }
+        }
+        return actualResult;
+    }
+
+    public static boolean findGivenElementInArrayUsingStream(int[] array, int element) {
+        return Arrays.stream(array).filter(x -> element == x).findFirst().isPresent();
+    }
+}

core-java/src/main/java/com/baeldung/array/SumAndAverageInArray.java

@@ -0,0 +1,27 @@
+package com.baeldung.array;
+
+import java.util.Arrays;
+
+public class SumAndAverageInArray {
+
+    public static int findSumWithoutUsingStream(int[] array) {
+        int sum = 0;
+        for (int index = 0; index < array.length; index++) {
+            sum += array[index];
+        }
+        return sum;
+    }
+
+    public static int findSumUsingStream(int[] array) {
+        return Arrays.stream(array).sum();
+    }
+
+    public static double findAverageWithoutUsingStream(int[] array) {
+        int sum = findSumWithoutUsingStream(array);
+        return (double) sum / array.length;
+    }
+
+    public static double findAverageUsingStream(int[] array) {
+        return Arrays.stream(array).average().getAsDouble();
+    }
+}

core-java/src/main/java/com/baeldung/asciiart/AsciiArt.java

@@ -0,0 +1,62 @@
+package com.baeldung.asciiart;
+
+import java.awt.Font;
+import java.awt.Graphics;
+import java.awt.Graphics2D;
+import java.awt.RenderingHints;
+import java.awt.image.BufferedImage;
+
+public class AsciiArt {
+
+    public AsciiArt() {
+    }
+
+    public void drawString(String text, String artChar, Settings settings) {
+        BufferedImage image = getImageIntegerMode(settings.width, settings.height);
+
+        Graphics2D graphics2D = getGraphics2D(image.getGraphics(), settings);
+        graphics2D.drawString(text, 6, ((int) (settings.height * 0.67)));
+
+        for (int y = 0; y < settings.height; y++) {
+            StringBuilder stringBuilder = new StringBuilder();
+
+            for (int x = 0; x < settings.width; x++) {
+                stringBuilder.append(image.getRGB(x, y) == -16777216 ? " " : artChar);
+            }
+
+            if (stringBuilder.toString()
+                .trim()
+                .isEmpty()) {
+                continue;
+            }
+
+            System.out.println(stringBuilder);
+        }
+
+    }
+
+    private BufferedImage getImageIntegerMode(int width, int height) {
+        return new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
+    }
+
+    private Graphics2D getGraphics2D(Graphics graphics, Settings settings) {
+        graphics.setFont(settings.font);
+
+        Graphics2D graphics2D = (Graphics2D) graphics;
+        graphics2D.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
+
+        return graphics2D;
+    }
+
+    public class Settings {
+        public Font font;
+        public int width;
+        public int height;
+
+        public Settings(Font font, int width, int height) {
+            this.font = font;
+            this.width = width;
+            this.height = height;
+        }
+    }
+}

core-java/src/main/java/com/baeldung/casting/Animal.java

@@ -0,0 +1,13 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Animal {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Animal.class);
+
+    public void eat() {
+        LOGGER.info("animal is eating");
+    }
+
+}

core-java/src/main/java/com/baeldung/casting/AnimalFeeder.java

@@ -0,0 +1,23 @@
+package com.baeldung.casting;
+
+import java.util.List;
+
+public class AnimalFeeder {
+
+    public void feed(List<Animal> animals) {
+        animals.forEach(animal -> {
+            animal.eat();
+            if (animal instanceof Cat) {
+                ((Cat) animal).meow();
+            }
+        });
+    }
+
+    public void uncheckedFeed(List<Animal> animals) {
+        animals.forEach(animal -> {
+            animal.eat();
+            ((Cat) animal).meow();
+        });
+    }
+
+}

core-java/src/main/java/com/baeldung/casting/AnimalFeederGeneric.java

@@ -0,0 +1,24 @@
+package com.baeldung.casting;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class AnimalFeederGeneric<T> {
+    private Class<T> type;
+
+    public AnimalFeederGeneric(Class<T> type) {
+        this.type = type;
+    }
+
+    public List<T> feed(List<Animal> animals) {
+        List<T> list = new ArrayList<T>();
+        animals.forEach(animal -> {
+            if (type.isInstance(animal)) {
+                T objAsType = type.cast(animal);
+                list.add(objAsType);
+            }
+        });
+        return list;
+    }
+
+}

core-java/src/main/java/com/baeldung/casting/Cat.java

@@ -0,0 +1,16 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Cat extends Animal implements Mew {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Cat.class);
+
+    public void eat() {
+        LOGGER.info("cat is eating");
+    }
+
+    public void meow() {
+        LOGGER.info("meow");
+    }
+}