Merge branch 'master' of https://github.com/eugenp/tutorials into task/BAEL-9467

.gitignore

@@ -62,3 +62,5 @@ jmeter/src/main/resources/*-JMeter.csv
 **/dist
 **/tmp
 **/out-tsc
+**/nbproject/
+**/nb-configuration.xml

README.md

@@ -21,3 +21,8 @@ In additional to Spring, the following technologies are in focus: `core Java`, `
 Building the project
 ====================
 To do the full build, do: `mvn install -Pdefault -Dgib.enabled=false`
+
+
+Building a single module
+====================
+To build a specific module run the command: `mvn clean install -Dgib.enabled=false` in the module directory

algorithms/README.md

@@ -28,3 +28,6 @@
 - [Calculate the Distance Between Two Points in Java](https://www.baeldung.com/java-distance-between-two-points)
 - [Find the Intersection of Two Lines in Java](https://www.baeldung.com/java-intersection-of-two-lines)
 - [Check If a String Contains All The Letters of The Alphabet](https://www.baeldung.com/java-string-contains-all-letters)
+- [Round Up to the Nearest Hundred](https://www.baeldung.com/java-round-up-nearest-hundred)
+- [Merge Sort in Java](https://www.baeldung.com/java-merge-sort)
+- [Calculate Percentage in Java](https://www.baeldung.com/java-calculate-percentage)

algorithms/pom.xml

@@ -17,6 +17,11 @@
             <artifactId>commons-math3</artifactId>
             <version>${commons-math3.version}</version>
         </dependency>
+        <dependency>
+            <groupId>commons-codec</groupId>
+            <artifactId>commons-codec</artifactId>
+            <version>${commons-codec.version}</version>
+        </dependency>
         <dependency>
             <groupId>org.projectlombok</groupId>
             <artifactId>lombok</artifactId>
@@ -85,6 +90,7 @@
         <io.jenetics.version>3.7.0</io.jenetics.version>
         <org.jgrapht.core.version>1.0.1</org.jgrapht.core.version>
         <org.assertj.core.version>3.9.0</org.assertj.core.version>
+        <commons-codec.version>1.11</commons-codec.version>
     </properties>
 
 </project>

algorithms/src/main/java/com/baeldung/algorithms/conversion/HexStringConverter.java

@@ -0,0 +1,110 @@
+package com.baeldung.algorithms.conversion;
+
+import java.math.BigInteger;
+
+import javax.xml.bind.DatatypeConverter;
+
+import org.apache.commons.codec.DecoderException;
+import org.apache.commons.codec.binary.Hex;
+
+import com.google.common.io.BaseEncoding;
+
+public class HexStringConverter {
+
+    /**
+     * Create a byte Array from String of hexadecimal digits using Character conversion 
+     * @param hexString - Hexadecimal digits as String
+     * @return Desired byte Array
+     */
+    public byte[] decodeHexString(String hexString) {
+        if (hexString.length() % 2 == 1) {
+            throw new IllegalArgumentException("Invalid hexadecimal String supplied.");
+        }
+        byte[] bytes = new byte[hexString.length() / 2];
+
+        for (int i = 0; i < hexString.length(); i += 2) {
+            bytes[i / 2] = hexToByte(hexString.substring(i, i + 2));
+        }
+        return bytes;
+    }
+
+    /**
+     * Create a String of hexadecimal digits from a byte Array using Character conversion
+     * @param byteArray - The byte Array
+     * @return Desired String of hexadecimal digits in lower case
+     */
+    public String encodeHexString(byte[] byteArray) {
+        StringBuffer hexStringBuffer = new StringBuffer();
+        for (int i = 0; i < byteArray.length; i++) {
+            hexStringBuffer.append(byteToHex(byteArray[i]));
+        }
+        return hexStringBuffer.toString();
+    }
+
+    public String byteToHex(byte num) {
+        char[] hexDigits = new char[2];
+        hexDigits[0] = Character.forDigit((num >> 4) & 0xF, 16);
+        hexDigits[1] = Character.forDigit((num & 0xF), 16);
+        return new String(hexDigits);
+    }
+
+    public byte hexToByte(String hexString) {
+        int firstDigit = toDigit(hexString.charAt(0));
+        int secondDigit = toDigit(hexString.charAt(1));
+        return (byte) ((firstDigit << 4) + secondDigit);
+    }
+
+    private int toDigit(char hexChar) {
+        int digit = Character.digit(hexChar, 16);
+        if(digit == -1) {
+            throw new IllegalArgumentException("Invalid Hexadecimal Character: "+ hexChar);
+        }
+        return digit;
+    }
+
+    public String encodeUsingBigIntegerToString(byte[] bytes) {
+        BigInteger bigInteger = new BigInteger(1, bytes);
+        return bigInteger.toString(16);
+    }
+
+    public String encodeUsingBigIntegerStringFormat(byte[] bytes) {
+        BigInteger bigInteger = new BigInteger(1, bytes);
+        return String.format("%0" + (bytes.length << 1) + "x", bigInteger);
+    }
+
+    public byte[] decodeUsingBigInteger(String hexString) {
+        byte[] byteArray = new BigInteger(hexString, 16).toByteArray();
+        if (byteArray[0] == 0) {
+            byte[] output = new byte[byteArray.length - 1];
+            System.arraycopy(byteArray, 1, output, 0, output.length);
+            return output;
+        }
+        return byteArray;
+    }
+
+    public String encodeUsingDataTypeConverter(byte[] bytes) {
+        return DatatypeConverter.printHexBinary(bytes);
+    }
+
+    public byte[] decodeUsingDataTypeConverter(String hexString) {
+        return DatatypeConverter.parseHexBinary(hexString);
+    }
+
+    public String encodeUsingApacheCommons(byte[] bytes) throws DecoderException {
+        return Hex.encodeHexString(bytes);
+    }
+
+    public byte[] decodeUsingApacheCommons(String hexString) throws DecoderException {
+        return Hex.decodeHex(hexString);
+    }
+
+    public String encodeUsingGuava(byte[] bytes) {
+        return BaseEncoding.base16()
+            .encode(bytes);
+    }
+
+    public byte[] decodeUsingGuava(String hexString) {
+        return BaseEncoding.base16()
+            .decode(hexString.toUpperCase());
+    }
+}

algorithms/src/test/java/com/baeldung/algorithms/conversion/ByteArrayConverterUnitTest.java

@@ -0,0 +1,127 @@
+package com.baeldung.algorithms.conversion;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+
+import org.apache.commons.codec.DecoderException;
+import org.hamcrest.text.IsEqualIgnoringCase;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.baeldung.algorithms.conversion.HexStringConverter;
+
+public class ByteArrayConverterUnitTest {
+
+    private HexStringConverter hexStringConverter;
+
+    @Before
+    public void setup() {
+        hexStringConverter = new HexStringConverter();
+    }
+
+    @Test
+    public void shouldEncodeByteArrayToHexStringUsingBigIntegerToString() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        if(hexString.charAt(0) == '0') {
+            hexString = hexString.substring(1);
+        }
+        String output = hexStringConverter.encodeUsingBigIntegerToString(bytes);
+        assertThat(output, IsEqualIgnoringCase.equalToIgnoringCase(hexString));
+    }
+
+    @Test
+    public void shouldEncodeByteArrayToHexStringUsingBigIntegerStringFormat() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        String output = hexStringConverter.encodeUsingBigIntegerStringFormat(bytes);
+        assertThat(output, IsEqualIgnoringCase.equalToIgnoringCase(hexString));
+    }
+
+    @Test
+    public void shouldDecodeHexStringToByteArrayUsingBigInteger() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        byte[] output = hexStringConverter.decodeUsingBigInteger(hexString);
+        assertArrayEquals(bytes, output);
+    }
+    
+    @Test
+    public void shouldEncodeByteArrayToHexStringUsingCharacterConversion() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        String output = hexStringConverter.encodeHexString(bytes);
+        assertThat(output, IsEqualIgnoringCase.equalToIgnoringCase(hexString));
+    }
+
+    @Test
+    public void shouldDecodeHexStringToByteArrayUsingCharacterConversion() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        byte[] output = hexStringConverter.decodeHexString(hexString);
+        assertArrayEquals(bytes, output);
+    }
+    
+    @Test(expected=IllegalArgumentException.class)
+    public void shouldDecodeHexToByteWithInvalidHexCharacter() {
+        hexStringConverter.hexToByte("fg");
+    }
+
+    @Test
+    public void shouldEncodeByteArrayToHexStringDataTypeConverter() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        String output = hexStringConverter.encodeUsingDataTypeConverter(bytes);
+        assertThat(output, IsEqualIgnoringCase.equalToIgnoringCase(hexString));
+    }
+
+    @Test
+    public void shouldDecodeHexStringToByteArrayUsingDataTypeConverter() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        byte[] output = hexStringConverter.decodeUsingDataTypeConverter(hexString);
+        assertArrayEquals(bytes, output);
+    }
+
+    @Test
+    public void shouldEncodeByteArrayToHexStringUsingGuava() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        String output = hexStringConverter.encodeUsingGuava(bytes);
+        assertThat(output, IsEqualIgnoringCase.equalToIgnoringCase(hexString));
+    }
+
+    @Test
+    public void shouldDecodeHexStringToByteArrayUsingGuava() {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        byte[] output = hexStringConverter.decodeUsingGuava(hexString);
+        assertArrayEquals(bytes, output);
+    }
+
+    @Test
+    public void shouldEncodeByteArrayToHexStringUsingApacheCommons() throws DecoderException {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        String output = hexStringConverter.encodeUsingApacheCommons(bytes);
+        assertThat(output, IsEqualIgnoringCase.equalToIgnoringCase(hexString));
+    }
+
+    @Test
+    public void shouldDecodeHexStringToByteArrayUsingApacheCommons() throws DecoderException {
+        byte[] bytes = getSampleBytes();
+        String hexString = getSampleHexString();
+        byte[] output = hexStringConverter.decodeUsingApacheCommons(hexString);
+        assertArrayEquals(bytes, output);
+    }
+
+    private String getSampleHexString() {
+        return "0af50c0e2d10";
+    }
+
+    private byte[] getSampleBytes() {
+        return new byte[] { 10, -11, 12, 14, 45, 16 };
+    }
+
+}

aws/README.md

@@ -9,4 +9,4 @@
 - [Integration Testing with a Local DynamoDB Instance](http://www.baeldung.com/dynamodb-local-integration-tests)
 - [Using the JetS3t Java Client With Amazon S3](http://www.baeldung.com/jets3t-amazon-s3)
 - [Managing Amazon SQS Queues in Java](http://www.baeldung.com/aws-queues-java)
-
+- [Guide to AWS Aurora RDS with Java](https://www.baeldung.com/aws-aurora-rds-java)

core-java-8/src/test/java/com/baeldung/internationalization/DateTimeFormatterUnitTest.java

@@ -1,46 +0,0 @@
-package com.baeldung.internationalization;
-
-import org.junit.Assert;
-import org.junit.Test;
-
-import java.time.LocalDateTime;
-import java.time.ZoneId;
-import java.time.ZonedDateTime;
-import java.time.format.DateTimeFormatter;
-import java.time.format.FormatStyle;
-import java.util.Locale;
-import java.util.TimeZone;
-
-public class DateTimeFormatterUnitTest {
-
-    @Test
-    public void givenDefaultUsLocaleAndDateTimeAndPattern_whenFormatWithDifferentLocales_thenGettingLocalizedDateTimes() {
-        Locale.setDefault(Locale.US);
-        LocalDateTime localDateTime = LocalDateTime.of(2018, 1, 1, 10, 15, 50, 500);
-        String pattern = "dd-MMMM-yyyy HH:mm:ss.SSS";
-
-        DateTimeFormatter defaultTimeFormatter = DateTimeFormatter.ofPattern(pattern);
-        DateTimeFormatter plTimeFormatter = DateTimeFormatter.ofPattern(pattern, new Locale("pl", "PL"));
-        DateTimeFormatter deTimeFormatter = DateTimeFormatter.ofPattern(pattern).withLocale(Locale.GERMANY);
-
-        Assert.assertEquals("01-January-2018 10:15:50.000", defaultTimeFormatter.format(localDateTime));
-        Assert.assertEquals("01-stycznia-2018 10:15:50.000", plTimeFormatter.format(localDateTime));
-        Assert.assertEquals("01-Januar-2018 10:15:50.000", deTimeFormatter.format(localDateTime));
-    }
-
-    @Test
-    public void givenDateTimeAndTimeZone_whenFormatWithDifferentLocales_thenGettingLocalizedZonedDateTimes() {
-        Locale.setDefault(Locale.US);
-        LocalDateTime localDateTime = LocalDateTime.of(2018, 1, 1, 10, 15, 50, 500);
-        ZoneId losAngelesTimeZone = TimeZone.getTimeZone("America/Los_Angeles").toZoneId();
-
-        DateTimeFormatter localizedFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL);
-        DateTimeFormatter frLocalizedFormatter =
-                DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).withLocale(Locale.FRANCE);
-        String formattedDateTime = localizedFormatter.format(ZonedDateTime.of(localDateTime, losAngelesTimeZone));
-        String frFormattedDateTime = frLocalizedFormatter.format(ZonedDateTime.of(localDateTime, losAngelesTimeZone));
-
-        Assert.assertEquals("Monday, January 1, 2018 10:15:50 AM PST", formattedDateTime);
-        Assert.assertEquals("lundi 1 janvier 2018 10 h 15 PST", frFormattedDateTime);
-    }
-}

core-java-9/README.md

@@ -26,3 +26,4 @@
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
+- [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)

core-java-collections/README.md

@@ -52,3 +52,6 @@
 - [Performance of contains() in a HashSet vs ArrayList](https://www.baeldung.com/java-hashset-arraylist-contains-performance)
 - [Get the Key for a Value from a Java Map](https://www.baeldung.com/java-map-key-from-value)
 - [Time Complexity of Java Collections](https://www.baeldung.com/java-collections-complexity)
+- [Sort a HashMap in Java](https://www.baeldung.com/java-hashmap-sort)
+- [Finding the Highest Value in a Java Map](https://www.baeldung.com/java-find-map-max)
+- [Operating on and Removing an Item from Stream](https://www.baeldung.com/java-use-remove-item-stream)

core-java-collections/pom.xml

@@ -1,7 +1,6 @@
 <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>core-java-collections</artifactId>
     <version>0.1.0-SNAPSHOT</version>
     <packaging>jar</packaging>
@@ -68,15 +67,14 @@
             <artifactId>commons-exec</artifactId>
             <version>1.3</version>
         </dependency>
+        
         <dependency>
             <groupId>one.util</groupId>
             <artifactId>streamex</artifactId>
             <version>0.6.5</version>
         </dependency>
-		        
     </dependencies>
 
-
     <properties>
         <openjdk.jmh.version>1.19</openjdk.jmh.version>
         <junit.platform.version>1.2.0</junit.platform.version>

core-java-collections/src/main/java/com/baeldung/convertcollectiontoarraylist/Foo.java

@@ -0,0 +1,52 @@
+package com.baeldung.convertcollectiontoarraylist;
+
+/**
+ * This POJO is the element type of our collection. It has a deepCopy() method.
+ *
+ * @author chris
+ */
+public class Foo {
+
+    private int id;
+    private String name;
+    private Foo parent;
+
+    public Foo() {
+    }
+
+    public Foo(int id, String name, Foo parent) {
+        this.id = id;
+        this.name = name;
+        this.parent = parent;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public Foo getParent() {
+        return parent;
+    }
+
+    public void setParent(Foo parent) {
+        this.parent = parent;
+    }
+
+    public Foo deepCopy() {
+        return new Foo(
+          this.id, this.name, this.parent != null ? this.parent.deepCopy() : null);
+    }
+
+}

core-java-collections/src/main/java/com/baeldung/enumset/EnumSets.java

@@ -0,0 +1,45 @@
+package com.baeldung.enumset;
+
+import java.util.ArrayList;
+import java.util.EnumSet;
+import java.util.List;
+
+public class EnumSets {
+
+    public enum Color {
+        RED, YELLOW, GREEN, BLUE, BLACK, WHITE
+    }
+
+    public static void main(String[] args) {
+        EnumSet<Color> allColors = EnumSet.allOf(Color.class);
+        System.out.println(allColors);
+
+        EnumSet<Color> noColors = EnumSet.noneOf(Color.class);
+        System.out.println(noColors);
+
+        EnumSet<Color> blackAndWhite = EnumSet.of(Color.BLACK, Color.WHITE);
+        System.out.println(blackAndWhite);
+
+        EnumSet<Color> noBlackOrWhite = EnumSet.complementOf(blackAndWhite);
+        System.out.println(noBlackOrWhite);
+
+        EnumSet<Color> range = EnumSet.range(Color.YELLOW, Color.BLUE);
+        System.out.println(range);
+
+        EnumSet<Color> blackAndWhiteCopy = EnumSet.copyOf(EnumSet.of(Color.BLACK, Color.WHITE));
+        System.out.println(blackAndWhiteCopy);
+
+        List<Color> colorsList = new ArrayList<>();
+        colorsList.add(Color.RED);
+        EnumSet<Color> listCopy = EnumSet.copyOf(colorsList);
+        System.out.println(listCopy);
+
+        EnumSet<Color> set = EnumSet.noneOf(Color.class);
+        set.add(Color.RED);
+        set.add(Color.YELLOW);
+        set.contains(Color.RED);
+        set.forEach(System.out::println);
+        set.remove(Color.RED);
+    }
+
+}

core-java-collections/src/main/java/com/baeldung/synchronizedcollections/application/Application.java

@@ -0,0 +1,18 @@
+package com.baeldung.synchronizedcollections.application;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.logging.Logger;
+
+public class Application {
+
+    private static final Logger LOGGER = Logger.getLogger(Application.class.getName());
+    
+    public static void main(String[] args) throws InterruptedException {
+        List<Integer> syncCollection = Collections.synchronizedList(Arrays.asList(1, 2, 3, 4, 5, 6));
+        synchronized (syncCollection) {
+            syncCollection.forEach((e) -> {LOGGER.info(e.toString());});
+        }
+    }
+}

core-java-collections/src/test/java/com/baeldung/convertcollectiontoarraylist/FooUnitTest.java

@@ -0,0 +1,148 @@
+package com.baeldung.convertcollectiontoarraylist;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.HashSet;
+import java.util.Iterator;
+import static java.util.stream.Collectors.toCollection;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ *
+ * @author chris
+ */
+public class FooUnitTest {
+    private static Collection<Foo> srcCollection = new HashSet<>();
+
+    public FooUnitTest() {
+    }
+    
+    @BeforeClass
+    public static void setUpClass() {
+        int i = 0;
+        Foo john = new Foo(i++, "John", null);
+        Foo mary = new Foo(i++, "Mary", null);
+        Foo sam = new Foo(i++, "Sam", john);
+        Foo alice = new Foo(i++, "Alice", john);
+        Foo buffy = new Foo(i++, "Buffy", sam);
+        srcCollection.add(john);
+        srcCollection.add(mary);
+        srcCollection.add(sam);
+        srcCollection.add(alice);
+        srcCollection.add(buffy);
+
+        // make sure the collection isn't sorted accidentally
+        assertFalse("Oops: source collection is already sorted!", isSorted(srcCollection));
+    }
+    
+    /**
+     * Section 3. Using the ArrayList Constructor
+     */
+    @Test
+    public void whenUsingConstructor_thenVerifyShallowCopy() {
+        ArrayList<Foo> newList = new ArrayList<>(srcCollection);
+        verifyShallowCopy(srcCollection, newList);
+    }
+    
+    /**
+     * Section 4. Using the Streams API
+     */
+    @Test
+    public void whenUsingStream_thenVerifyShallowCopy() {
+        ArrayList<Foo> newList = srcCollection.stream().collect(toCollection(ArrayList::new));
+
+        verifyShallowCopy(srcCollection, newList);
+    }
+    
+    /**
+     * Section 5. Deep Copy
+     */
+    @Test
+    public void whenUsingDeepCopy_thenVerifyDeepCopy() {
+        ArrayList<Foo> newList = srcCollection.stream()
+          .map(foo -> foo.deepCopy())
+          .collect(toCollection(ArrayList::new));
+
+        verifyDeepCopy(srcCollection, newList);
+    }
+    
+    /**
+     * Section 6. Controlling the List Order
+     */
+    @Test
+    public void whenUsingSortedStream_thenVerifySortOrder() {
+        ArrayList<Foo> newList = srcCollection.stream()
+          .sorted(Comparator.comparing(Foo::getName))
+          .collect(toCollection(ArrayList::new));
+
+        assertTrue("ArrayList is not sorted by name", isSorted(newList));
+    }
+    
+    /**
+     * Verify that the contents of the two collections are the same
+     * @param a
+     * @param b 
+     */
+    private void verifyShallowCopy(Collection a, Collection b) {
+        assertEquals("Collections have different lengths", a.size(), b.size());
+        Iterator<Foo> iterA = a.iterator();
+        Iterator<Foo> iterB = b.iterator();
+        while (iterA.hasNext()) {
+            // use '==' to test instance identity
+            assertTrue("Foo instances differ!", iterA.next() == iterB.next());
+        }
+    }
+    
+    /**
+     * Verify that the contents of the two collections are the same
+     * @param a
+     * @param b 
+     */
+    private void verifyDeepCopy(Collection a, Collection b) {
+        assertEquals("Collections have different lengths", a.size(), b.size());
+        Iterator<Foo> iterA = a.iterator();
+        Iterator<Foo> iterB = b.iterator();
+        while (iterA.hasNext()) {
+            Foo nextA = iterA.next();
+            Foo nextB = iterB.next();
+            // should not be same instance
+            assertFalse("Foo instances are the same!", nextA == nextB);
+            // but should have same content
+            assertFalse("Foo instances have different content!", fooDiff(nextA, nextB));
+        }
+    }
+
+    /**
+     * Return true if the contents of a and b differ.  Test parent recursively
+     * @param a
+     * @param b
+     * @return False if the two items are the same
+     */
+    private boolean fooDiff(Foo a, Foo b) {
+        if (a != null && b != null) {
+            return a.getId() != b.getId() 
+              || !a.getName().equals(b.getName()) 
+              || fooDiff(a.getParent(), b.getParent());
+        }
+        return !(a == null && b == null);
+    }
+    
+    /**
+     * @param c collection of Foo
+     * @return true if the collection is sorted by name
+     */
+    private static boolean isSorted(Collection<Foo> c) {
+        String prevName = null;
+        for (Foo foo : c) {
+            if (prevName == null || foo.getName().compareTo(prevName) > 0) {
+                prevName = foo.getName();
+            } else {
+                return false;
+            }
+        }
+        return true;
+    }
+}

core-java-collections/src/test/java/com/baeldung/findItems/FindItemsBasedOnOtherStreamUnitTest.java

@@ -0,0 +1,89 @@
+package com.baeldung.findItems;
+
+import static org.junit.Assert.assertEquals;
+
+import java.text.ParseException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Test;
+
+public class FindItemsBasedOnOtherStreamUnitTest {
+
+    private List<Employee> employeeList = new ArrayList<Employee>();
+
+    private List<Department> departmentList = new ArrayList<Department>();
+
+    @Test
+    public void givenDepartmentList_thenEmployeeListIsFilteredCorrectly() {
+        Integer expectedId = 1002;
+
+        populate(employeeList, departmentList);
+
+        List<Employee> filteredList = employeeList.stream()
+            .filter(empl -> departmentList.stream()
+                .anyMatch(dept -> dept.getDepartment()
+                    .equals("sales") && empl.getEmployeeId()
+                    .equals(dept.getEmployeeId())))
+            .collect(Collectors.toList());
+
+        assertEquals(expectedId, filteredList.get(0)
+            .getEmployeeId());
+    }
+
+    private void populate(List<Employee> EmplList, List<Department> deptList) {
+        Employee employee1 = new Employee(1001, "empl1");
+        Employee employee2 = new Employee(1002, "empl2");
+        Employee employee3 = new Employee(1003, "empl3");
+
+        Collections.addAll(EmplList, employee1, employee2, employee3);
+
+        Department department1 = new Department(1002, "sales");
+        Department department2 = new Department(1003, "marketing");
+        Department department3 = new Department(1004, "sales");
+
+        Collections.addAll(deptList, department1, department2, department3);
+    }
+}
+
+class Employee {
+    private Integer employeeId;
+    private String employeeName;
+
+    Employee(Integer employeeId, String employeeName) {
+        super();
+        this.employeeId = employeeId;
+        this.employeeName = employeeName;
+    }
+
+    Integer getEmployeeId() {
+        return employeeId;
+    }
+
+    public String getEmployeeName() {
+        return employeeName;
+    }
+
+}
+
+class Department {
+    private Integer employeeId;
+    private String department;
+
+    Department(Integer employeeId, String department) {
+        super();
+        this.employeeId = employeeId;
+        this.department = department;
+    }
+
+    Integer getEmployeeId() {
+        return employeeId;
+    }
+
+    String getDepartment() {
+        return department;
+    }
+
+}

core-java-collections/src/test/java/com/baeldung/java/map/KeyCheckTest.java

@@ -1,44 +0,0 @@
-package com.baeldung.java.map;
-
-import static org.assertj.core.api.Assertions.assertThat;
-
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
-import org.apache.commons.collections4.MultiMap;
-import org.apache.commons.collections4.MultiMapUtils;
-import org.apache.commons.collections4.MultiValuedMap;
-import org.apache.commons.collections4.map.MultiValueMap;
-import org.apache.commons.collections4.multimap.ArrayListValuedHashMap;
-import org.apache.commons.collections4.multimap.HashSetValuedHashMap;
-import org.junit.Test;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import com.google.common.collect.ArrayListMultimap;
-import com.google.common.collect.LinkedHashMultimap;
-import com.google.common.collect.Multimap;
-import com.google.common.collect.TreeMultimap;
-
-
-public class KeyCheckTest {
-
-    @Test
-    public void whenKeyIsPresent_thenContainsKeyReturnsTrue() {
-        Map<String, String> map = Collections.singletonMap("key", "value");
-
-        assertTrue(map.containsKey("key"));
-        assertFalse(map.containsKey("missing"));
-    }
-
-    @Test
-    public void whenKeyHasNullValue_thenGetStillWorks() {
-        Map<String, String> map = Collections.singletonMap("nothing", null);
-
-        assertTrue(map.containsKey("nothing"));
-        assertNull(map.get("nothing"));
-    }
-}

core-java-collections/src/test/java/com/baeldung/java/map/KeyCheckUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.java.map;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.Test;
+
+public class KeyCheckUnitTest {
+
+    @Test
+    public void whenKeyIsPresent_thenContainsKeyReturnsTrue() {
+        Map<String, String> map = Collections.singletonMap("key", "value");
+
+        assertTrue(map.containsKey("key"));
+        assertFalse(map.containsKey("missing"));
+    }
+
+    @Test
+    public void whenKeyHasNullValue_thenGetStillWorks() {
+        Map<String, String> map = Collections.singletonMap("nothing", null);
+
+        assertTrue(map.containsKey("nothing"));
+        assertNull(map.get("nothing"));
+    }
+}

core-java-collections/src/test/java/com/baeldung/synchronizedcollections/test/SynchronizedCollectionUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.synchronizedcollections.test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class SynchronizedCollectionUnitTest {
+
+    @Test
+    public void givenSynchronizedCollection_whenTwoThreadsAddElements_thenCorrectCollectionSize() throws InterruptedException {
+        Collection<Integer> syncCollection = Collections.synchronizedCollection(new ArrayList<>());
+
+        Runnable listOperations = () -> {
+            syncCollection.addAll(Arrays.asList(1, 2, 3, 4, 5, 6));
+        };
+        Thread thread1 = new Thread(listOperations);
+        Thread thread2 = new Thread(listOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+
+        assertThat(syncCollection.size()).isEqualTo(12);
+    }
+}

core-java-collections/src/test/java/com/baeldung/synchronizedcollections/test/SynchronizedListUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.synchronizedcollections.test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class SynchronizedListUnitTest {
+
+    @Test
+    public void givenSynchronizedList_whenTwoThreadsAddElements_thenCorrectListSize() throws InterruptedException {
+        List<Integer> syncList = Collections.synchronizedList(new ArrayList<>());
+
+        Runnable listOperations = () -> {
+            syncList.addAll(Arrays.asList(1, 2, 3, 4, 5, 6));
+        };
+        Thread thread1 = new Thread(listOperations);
+        Thread thread2 = new Thread(listOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+        
+        assertThat(syncList.size()).isEqualTo(12);
+    }
+    
+    @Test
+    public void givenStringList_whenTwoThreadsIterateOnSynchronizedList_thenCorrectResult() throws InterruptedException {
+        List<String> syncCollection = Collections.synchronizedList(Arrays.asList("a", "b", "c"));
+        List<String> uppercasedCollection = new ArrayList<>();
+
+        Runnable listOperations = () -> {
+            synchronized (syncCollection) {
+                syncCollection.forEach((e) -> {
+                    uppercasedCollection.add(e.toUpperCase());
+                });
+            }
+        };
+        
+        Thread thread1 = new Thread(listOperations);
+        Thread thread2 = new Thread(listOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+        
+        assertThat(uppercasedCollection.get(0)).isEqualTo("A");
+    }
+}

core-java-collections/src/test/java/com/baeldung/synchronizedcollections/test/SynchronizedMapUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.synchronizedcollections.test;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class SynchronizedMapUnitTest {
+
+    @Test
+    public void givenSynchronizedMap_whenTwoThreadsAddElements_thenCorrectMapSize() throws InterruptedException {
+        Map<Integer, String> syncMap = Collections.synchronizedMap(new HashMap<>());
+
+        Runnable mapOperations = () -> {
+            syncMap.put(1, "one");
+            syncMap.put(2, "two");
+            syncMap.put(3, "three");
+            
+        };
+        Thread thread1 = new Thread(mapOperations);
+        Thread thread2 = new Thread(mapOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+        
+        assertThat(syncMap.size()).isEqualTo(3);
+    }
+}

core-java-collections/src/test/java/com/baeldung/synchronizedcollections/test/SynchronizedSetUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.synchronizedcollections.test;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
+
+public class SynchronizedSetUnitTest {
+    
+    @Test
+    public void givenSynchronizedSet_whenTwoThreadsAddElements_thenCorrectSetSize() throws InterruptedException {
+        Set<Integer> syncSet = Collections.synchronizedSet(new HashSet<>());
+        
+        Runnable setOperations = () -> {syncSet.addAll(Arrays.asList(1, 2, 3, 4, 5, 6));};
+        Thread thread1 = new Thread(setOperations);
+        Thread thread2 = new Thread(setOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+        
+        assertThat(syncSet.size()).isEqualTo(6);
+    }
+}

core-java-collections/src/test/java/com/baeldung/synchronizedcollections/test/SynchronizedSortedMapUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.synchronizedcollections.test;
+
+import java.util.Collections;
+import java.util.Map;
+import java.util.TreeMap;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class SynchronizedSortedMapUnitTest {
+    
+    @Test
+    public void givenSynchronizedSorteMap_whenTwoThreadsAddElements_thenCorrectSortedMapSize() throws InterruptedException {
+        Map<Integer, String> syncSortedMap = Collections.synchronizedSortedMap(new TreeMap<>());
+        
+        Runnable sortedMapOperations = () -> {
+            syncSortedMap.put(1, "One");
+            syncSortedMap.put(2, "Two");
+            syncSortedMap.put(3, "Three");
+        };
+        Thread thread1 = new Thread(sortedMapOperations);
+        Thread thread2 = new Thread(sortedMapOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+        
+        assertThat(syncSortedMap.size()).isEqualTo(3);
+    }
+}

core-java-collections/src/test/java/com/baeldung/synchronizedcollections/test/SynchronizedSortedSetUnitTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.synchronizedcollections.test;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.SortedSet;
+import java.util.TreeSet;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class SynchronizedSortedSetUnitTest {
+    
+    @Test
+    public void givenSynchronizedSortedSet_whenTwoThreadsAddElements_thenCorrectSortedSetSize() throws InterruptedException {
+        SortedSet<Integer> syncSortedSet = Collections.synchronizedSortedSet(new TreeSet<>());
+        
+        Runnable sortedSetOperations = () -> {syncSortedSet.addAll(Arrays.asList(1, 2, 3, 4, 5, 6));};
+        sortedSetOperations.run();
+        sortedSetOperations.run();
+        Thread thread1 = new Thread(sortedSetOperations);
+        Thread thread2 = new Thread(sortedSetOperations);
+        thread1.start();
+        thread2.start();
+        thread1.join();
+        thread2.join();
+        
+        assertThat(syncSortedSet.size()).isEqualTo(6);
+    }
+}

core-java-concurrency/README.md

@@ -29,3 +29,4 @@
 - [A Custom Spring SecurityConfigurer](http://www.baeldung.com/spring-security-custom-configurer)
 - [Life Cycle of a Thread in Java](http://www.baeldung.com/java-thread-lifecycle)
 - [Runnable vs. Callable in Java](http://www.baeldung.com/java-runnable-callable)
+- [Brief Introduction to Java Thread.yield()](https://www.baeldung.com/java-thread-yield)

core-java-concurrency/src/test/java/com/baeldung/completablefuture/CompletableFutureLongRunningUnitTest.java

@@ -185,4 +185,24 @@ public class CompletableFutureLongRunningUnitTest {
         assertEquals("Hello World", future.get());
     }
     
+    @Test
+    public void whenPassingTransformation_thenFunctionExecutionWithThenApply() throws InterruptedException, ExecutionException {
+        CompletableFuture<Integer> finalResult = compute().thenApply(s -> s + 1);
+        assertTrue(finalResult.get() == 11);
+    }
+    
+    @Test
+    public void whenPassingPreviousStage_thenFunctionExecutionWithThenCompose() throws InterruptedException, ExecutionException {
+        CompletableFuture<Integer> finalResult = compute().thenCompose(this::computeAnother);
+        assertTrue(finalResult.get() == 20);
+    }
+    
+    public CompletableFuture<Integer> compute(){
+        return CompletableFuture.supplyAsync(() -> 10);
+    }
+    
+    public CompletableFuture<Integer> computeAnother(Integer i){
+        return CompletableFuture.supplyAsync(() -> 10 + i);
+    }
+
 }

core-java-io/src/main/resources/zipTest/test1.txt

@@ -0,0 +1 @@
+Test1

core-java-io/src/main/resources/zipTest/test2.txt

@@ -0,0 +1 @@
+Test2

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

@@ -8,7 +8,7 @@ import java.io.IOException;
 import org.junit.Before;
 import org.junit.Test;
 
-public class OutputStreamExamplesTest {
+public class OutputStreamExamplesUnitTest {
     
     StringBuilder filePath = new StringBuilder();
     

core-java/README.md

@@ -150,3 +150,9 @@
 - [Throw Exception in Optional in Java 8](https://www.baeldung.com/java-optional-throw-exception)
 - [Add a Character to a String at a Given Position](https://www.baeldung.com/java-add-character-to-string)
 - [Synthetic Constructs in Java](https://www.baeldung.com/java-synthetic)
+- [Convert Double to String, Removing Decimal Places](https://www.baeldung.com/java-double-to-string)
+- [Different Ways to Capture Java Heap Dumps](https://www.baeldung.com/java-heap-dump-capture)
+- [How to Separate Double into Integer and Decimal Parts](https://www.baeldung.com/java-separate-double-into-integer-decimal-parts)
+- [ZoneOffset in Java](https://www.baeldung.com/java-zone-offset)
+- [Hashing a Password in Java](https://www.baeldung.com/java-password-hashing)
+- [Java Switch Statement](https://www.baeldung.com/java-switch)

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

@@ -0,0 +1,159 @@
+package com.baeldung.array;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class ArrayReferenceGuide {
+
+    public static void main(String[] args) {
+        declaration();
+
+        initialization();
+
+        access();
+
+        iterating();
+
+        varargs();
+
+        transformIntoList();
+
+        transformIntoStream();
+
+        sort();
+
+        search();
+
+        merge();
+    }
+
+    private static void declaration() {
+        int[] anArray;
+        int anotherArray[];
+    }
+
+    private static void initialization() {
+        int[] anArray = new int[10];
+        anArray[0] = 10;
+        anArray[5] = 4;
+
+        int[] anotherArray = new int[] {1, 2, 3, 4, 5};
+    }
+
+    private static void access() {
+        int[] anArray = new int[10];
+        anArray[0] = 10;
+        anArray[5] = 4;
+
+        System.out.println(anArray[0]);
+    }
+
+    private static void iterating() {
+        int[] anArray = new int[] {1, 2, 3, 4, 5};
+        for (int i = 0; i < anArray.length; i++) {
+            System.out.println(anArray[i]);
+        }
+
+        for (int element : anArray) {
+            System.out.println(element);
+        }
+    }
+
+    private static void varargs() {
+        String[] groceries = new String[] {"Milk", "Tomato", "Chips"};
+        varargMethod(groceries);
+        varargMethod("Milk", "Tomato", "Chips");
+    }
+
+    private static void varargMethod(String... varargs) {
+        for (String element : varargs) {
+            System.out.println(element);
+        }
+    }
+
+    private static void transformIntoList() {
+        Integer[] anArray = new Integer[] {1, 2, 3, 4, 5};
+
+        // Naïve implementation
+        List<Integer> aList = new ArrayList<>(); // We create an empty list
+        for (int element : anArray) {
+            // We iterate over array's elements and add them to the list
+            aList.add(element);
+        }
+
+        // Pretty implementation
+        aList = Arrays.asList(anArray);
+
+        // Drawbacks
+        try {
+            aList.remove(0);
+        } catch (UnsupportedOperationException e) {
+            System.out.println(e.getMessage());
+        }
+
+        try {
+            aList.add(6);
+        } catch (UnsupportedOperationException e) {
+            System.out.println(e.getMessage());
+        }
+
+        int[] anotherArray = new int[] {1, 2, 3, 4, 5};
+//        List<Integer> anotherList = Arrays.asList(anotherArray);
+    }
+
+    private static void transformIntoStream() {
+        int[] anArray = new int[] {1, 2, 3, 4, 5};
+        IntStream aStream = Arrays.stream(anArray);
+
+        Integer[] anotherArray = new Integer[] {1, 2, 3, 4, 5};
+        Stream<Integer> anotherStream = Arrays.stream(anotherArray, 2, 4);
+    }
+
+    private static void sort() {
+        int[] anArray = new int[] {5, 2, 1, 4, 8};
+        Arrays.sort(anArray); // anArray is now {1, 2, 4, 5, 8}
+
+        Integer[] anotherArray = new Integer[] {5, 2, 1, 4, 8};
+        Arrays.sort(anotherArray); // anArray is now {1, 2, 4, 5, 8}
+
+        String[] yetAnotherArray = new String[] {"A", "E", "Z", "B", "C"};
+        Arrays.sort(yetAnotherArray, 1, 3, Comparator.comparing(String::toString).reversed()); // yetAnotherArray is now {"A", "Z", "E", "B", "C"}
+    }
+
+    private static void search() {
+        int[] anArray = new int[] {5, 2, 1, 4, 8};
+        for (int i = 0; i < anArray.length; i++) {
+            if (anArray[i] == 4) {
+                System.out.println("Found at index " + i);
+                break;
+            }
+        }
+
+        Arrays.sort(anArray);
+        int index = Arrays.binarySearch(anArray, 4);
+        System.out.println("Found at index " + index);
+    }
+
+    private static void merge() {
+        int[] anArray = new int[] {5, 2, 1, 4, 8};
+        int[] anotherArray = new int[] {10, 4, 9, 11, 2};
+
+        int[] resultArray = new int[anArray.length + anotherArray.length];
+        for (int i = 0; i < resultArray.length; i++) {
+            resultArray[i] = (i < anArray.length ? anArray[i] : anotherArray[i - anArray.length]);
+        }
+        for (int element : resultArray) {
+            System.out.println(element);
+        }
+
+        Arrays.setAll(resultArray, i -> (i < anArray.length ? anArray[i] : anotherArray[i - anArray.length]));
+        for (int element : resultArray) {
+            System.out.println(element);
+        }
+    }
+
+}

core-java/src/main/java/com/baeldung/classloader/CustomClassLoader.java

@@ -1,11 +1,14 @@
 package com.baeldung.classloader;
 
-import java.io.*;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
 
 public class CustomClassLoader extends ClassLoader {
 
-
+    @Override
-    public Class getClass(String name) throws ClassNotFoundException {
+    public Class findClass(String name) throws ClassNotFoundException {
         byte[] b = loadClassFromFile(name);
         return defineClass(name, b, 0, b.length);
     }

core-java/src/main/java/com/baeldung/heapsort/Heap.java

@@ -0,0 +1,136 @@
+package com.baeldung.heapsort;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Heap<E extends Comparable<E>> {
+
+    private List<E> elements = new ArrayList<>();
+
+    public static <E extends Comparable<E>> List<E> sort(Iterable<E> elements) {
+        Heap<E> heap = of(elements);
+
+        List<E> result = new ArrayList<>();
+
+        while (!heap.isEmpty()) {
+            result.add(heap.pop());
+        }
+
+        return result;
+    }
+
+    public static <E extends Comparable<E>> Heap<E> of(E... elements) {
+        return of(Arrays.asList(elements));
+    }
+
+    public static <E extends Comparable<E>> Heap<E> of(Iterable<E> elements) {
+        Heap<E> result = new Heap<>();
+        for (E element : elements) {
+            result.add(element);
+        }
+        return result;
+    }
+
+    public void add(E e) {
+        elements.add(e);
+        int elementIndex = elements.size() - 1;
+        while (!isRoot(elementIndex) && !isCorrectChild(elementIndex)) {
+            int parentIndex = parentIndex(elementIndex);
+            swap(elementIndex, parentIndex);
+            elementIndex = parentIndex;
+        }
+    }
+
+    public E pop() {
+        if (isEmpty()) {
+            throw new IllegalStateException("You cannot pop from an empty heap");
+        }
+
+        E result = elementAt(0);
+
+        int lasElementIndex = elements.size() - 1;
+        swap(0, lasElementIndex);
+        elements.remove(lasElementIndex);
+
+        int elementIndex = 0;
+        while (!isLeaf(elementIndex) && !isCorrectParent(elementIndex)) {
+            int smallerChildIndex = smallerChildIndex(elementIndex);
+            swap(elementIndex, smallerChildIndex);
+            elementIndex = smallerChildIndex;
+        }
+
+        return result;
+    }
+
+    public boolean isEmpty() {
+        return elements.isEmpty();
+    }
+    
+    private boolean isRoot(int index) {
+        return index == 0;
+    }
+
+    private int smallerChildIndex(int index) {
+        int leftChildIndex = leftChildIndex(index);
+        int rightChildIndex = rightChildIndex(index);
+        
+        if (!isValidIndex(rightChildIndex)) {
+            return leftChildIndex;
+        }
+
+        if (elementAt(leftChildIndex).compareTo(elementAt(rightChildIndex)) < 0) {
+            return leftChildIndex;
+        }
+
+        return rightChildIndex;
+    }
+
+    private boolean isLeaf(int index) {
+        return !isValidIndex(leftChildIndex(index));
+    }
+
+    private boolean isCorrectParent(int index) {
+        return isCorrect(index, leftChildIndex(index)) && isCorrect(index, rightChildIndex(index));
+    }
+
+    private boolean isCorrectChild(int index) {
+        return isCorrect(parentIndex(index), index);
+    }
+
+    private boolean isCorrect(int parentIndex, int childIndex) {
+        if (!isValidIndex(parentIndex) || !isValidIndex(childIndex)) {
+            return true;
+        }
+
+        return elementAt(parentIndex).compareTo(elementAt(childIndex)) < 0;
+    }
+
+    private boolean isValidIndex(int index) {
+        return index < elements.size();
+    }
+
+    private void swap(int index1, int index2) {
+        E element1 = elementAt(index1);
+        E element2 = elementAt(index2);
+        elements.set(index1, element2);
+        elements.set(index2, element1);
+    }
+
+    private E elementAt(int index) {
+        return elements.get(index);
+    }
+
+    private int parentIndex(int index) {
+        return (index - 1) / 2;
+    }
+
+    private int leftChildIndex(int index) {
+        return 2 * index + 1;
+    }
+
+    private int rightChildIndex(int index) {
+        return 2 * index + 2;
+    }
+
+}

core-java/src/test/java/com/baeldung/classloader/CustomClassLoaderUnitTest.java

@@ -11,7 +11,7 @@ public class CustomClassLoaderUnitTest {
     public void customLoader() throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {
 
         CustomClassLoader customClassLoader = new CustomClassLoader();
-        Class<?> c = customClassLoader.getClass(PrintClassLoader.class.getName());
+        Class<?> c = customClassLoader.findClass(PrintClassLoader.class.getName());
 
         Object ob = c.newInstance();
 

core-java/src/test/java/com/baeldung/heapsort/HeapUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.heapsort;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+public class HeapUnitTest {
+
+    @Test
+    public void givenNotEmptyHeap_whenPopCalled_thenItShouldReturnSmallestElement() {
+        // given
+        Heap<Integer> heap = Heap.of(3, 5, 1, 4, 2);
+
+        // when
+        int head = heap.pop();
+
+        // then
+        assertThat(head).isEqualTo(1);
+    }
+    
+    @Test
+    public void givenNotEmptyIterable_whenSortCalled_thenItShouldReturnElementsInSortedList() {
+        // given
+        List<Integer> elements = Arrays.asList(3, 5, 1, 4, 2);
+        
+        // when
+        List<Integer> sortedElements = Heap.sort(elements);
+        
+        // then
+        assertThat(sortedElements).isEqualTo(Arrays.asList(1, 2, 3, 4, 5));
+    }
+
+}

core-java/src/test/java/com/baeldung/modulo/ModuloUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.modulo;
+
+import org.junit.Test;
+import static org.assertj.core.api.Java6Assertions.*;
+
+public class ModuloUnitTest {
+
+  @Test
+  public void whenIntegerDivision_thenLosesRemainder(){
+    assertThat(11 / 4).isEqualTo(2);
+  }
+
+  @Test
+  public void whenDoubleDivision_thenKeepsRemainder(){
+    assertThat(11 / 4.0).isEqualTo(2.75);
+  }
+
+  @Test
+  public void whenModulo_thenReturnsRemainder(){
+    assertThat(11 % 4).isEqualTo(3);
+  }
+
+  @Test(expected = ArithmeticException.class)
+  public void whenDivisionByZero_thenArithmeticException(){
+    double result = 1 / 0;
+  }
+
+  @Test(expected = ArithmeticException.class)
+  public void whenModuloByZero_thenArithmeticException(){
+    double result = 1 % 0;
+  }
+
+  @Test
+  public void whenDivisorIsOddAndModulusIs2_thenResultIs1(){
+    assertThat(3 % 2).isEqualTo(1);
+  }
+
+  @Test
+  public void whenDivisorIsEvenAndModulusIs2_thenResultIs0(){
+    assertThat(4 % 2).isEqualTo(0);
+  }
+
+  @Test
+  public void whenItemsIsAddedToCircularQueue_thenNoArrayIndexOutOfBounds(){
+    int QUEUE_CAPACITY= 10;
+    int[] circularQueue = new int[QUEUE_CAPACITY];
+    int itemsInserted = 0;
+    for (int value = 0; value < 1000; value++) {
+      int writeIndex = ++itemsInserted % QUEUE_CAPACITY;
+      circularQueue[writeIndex] = value;
+    }
+  }
+
+}

core-java/src/test/java/com/baeldung/nth/root/calculator/NthRootCalculatorUnitTest.java

@@ -1,11 +1,11 @@
 package com.baeldung.nth.root.calculator;
 
+import static org.junit.Assert.assertEquals;
+
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.InjectMocks;
-import org.mockito.runners.MockitoJUnitRunner;
+import org.mockito.junit.MockitoJUnitRunner;
-
-import static org.junit.Assert.assertEquals;
 
 @RunWith(MockitoJUnitRunner.class)
 public class NthRootCalculatorUnitTest {

core-kotlin/README.md

@@ -37,3 +37,5 @@
 - [Kotlin with Ktor](https://www.baeldung.com/kotlin-ktor)
 - [Fuel HTTP Library with Kotlin](https://www.baeldung.com/kotlin-fuel)
 - [Introduction to Kovenant Library for Kotlin](https://www.baeldung.com/kotlin-kovenant)
+- [Converting Kotlin Data Class from JSON using GSON](https://www.baeldung.com/kotlin-json-convert-data-class)
+- [Concatenate Strings in Kotlin](https://www.baeldung.com/kotlin-concatenate-strings)

core-kotlin/src/main/kotlin/com/baeldung/datastructures/Main.kt

@@ -0,0 +1,19 @@
+package com.baeldung.datastructures
+
+/**
+ * Example of how to use the {@link Node} class.
+ *
+ */
+fun main(args: Array<String>) {
+    val tree = Node(4)
+    val keys = arrayOf(8, 15, 21, 3, 7, 2, 5, 10, 2, 3, 4, 6, 11)
+    for (key in keys) {
+        tree.insert(key)
+    }
+    val node = tree.find(4)!!
+    println("Node with value ${node.key} [left = ${node.left?.key}, right = ${node.right?.key}]")
+    println("Delete node with key = 3")
+    node.delete(3)
+    print("Tree content after the node elimination: ")
+    println(tree.visit().joinToString { it.toString() })
+}

core-kotlin/src/main/kotlin/com/baeldung/datastructures/Node.kt

@@ -0,0 +1,167 @@
+package com.baeldung.datastructures
+
+/**
+ * An ADT for a binary search tree.
+ * Note that this data type is neither immutable nor thread safe.
+ */
+class Node(
+        var key: Int,
+        var left: Node? = null,
+        var right: Node? = null) {
+
+    /**
+     * Return a node with given value. If no such node exists, return null.
+     * @param value
+     */
+    fun find(value: Int): Node? = when {
+        this.key > value -> left?.find(value)
+        this.key < value -> right?.find(value)
+        else -> this
+
+    }
+
+    /**
+     * Insert a given value into the tree.
+     * After insertion, the tree should contain a node with the given value.
+     * If the tree already contains the given value, nothing is performed.
+     * @param value
+     */
+    fun insert(value: Int) {
+        if (value > this.key) {
+            if (this.right == null) {
+                this.right = Node(value)
+            } else {
+                this.right?.insert(value)
+            }
+        } else if (value < this.key) {
+            if (this.left == null) {
+                this.left = Node(value)
+            } else {
+                this.left?.insert(value)
+            }
+        }
+    }
+
+    /**
+     * Delete the value from the given tree. If the tree does not contain the value, the tree remains unchanged.
+     * @param value
+     */
+    fun delete(value: Int) {
+        when {
+            value > key -> scan(value, this.right, this)
+            value < key -> scan(value, this.left, this)
+            else -> removeNode(this, null)
+        }
+    }
+
+    /**
+     * Scan the tree in the search of the given value.
+     * @param value
+     * @param node sub-tree that potentially might contain the sought value
+     * @param parent node's parent
+     */
+    private fun scan(value: Int, node: Node?, parent: Node?) {
+        if (node == null) {
+            System.out.println("value " + value
+                    + " seems not present in the tree.")
+            return
+        }
+        when {
+            value > node.key -> scan(value, node.right, node)
+            value < node.key -> scan(value, node.left, node)
+            value == node.key -> removeNode(node, parent)
+        }
+
+    }
+
+    /**
+     * Remove the node.
+     *
+     * Removal process depends on how many children the node has.
+     *
+     * @param node node that is to be removed
+     * @param parent parent of the node to be removed
+     */
+    private fun removeNode(node: Node, parent: Node?) {
+        node.left?.let { leftChild ->
+            run {
+                node.right?.let {
+                    removeTwoChildNode(node)
+                } ?: removeSingleChildNode(node, leftChild)
+            }
+        } ?: run {
+            node.right?.let { rightChild -> removeSingleChildNode(node, rightChild) } ?: removeNoChildNode(node, parent)
+        }
+
+
+    }
+
+    /**
+     * Remove the node without children.
+     * @param node
+     * @param parent
+     */
+    private fun removeNoChildNode(node: Node, parent: Node?) {
+        parent?.let { p ->
+            if (node == p.left) {
+                p.left = null
+            } else if (node == p.right) {
+                p.right = null
+            }
+        } ?: throw IllegalStateException(
+                "Can not remove the root node without child nodes")
+
+    }
+
+    /**
+     * Remove a node that has two children.
+     *
+     * The process of elimination is to find the biggest key in the left sub-tree and replace the key of the
+     * node that is to be deleted with that key.
+     */
+    private fun removeTwoChildNode(node: Node) {
+        val leftChild = node.left!!
+        leftChild.right?.let {
+            val maxParent = findParentOfMaxChild(leftChild)
+            maxParent.right?.let {
+                node.key = it.key
+                maxParent.right = null
+            } ?: throw IllegalStateException("Node with max child must have the right child!")
+
+        } ?: run {
+            node.key = leftChild.key
+            node.left = leftChild.left
+        }
+
+    }
+
+    /**
+     * Return a node whose right child contains the biggest value in the given sub-tree.
+     * Assume that the node n has a non-null right child.
+     *
+     * @param n
+     */
+    private fun findParentOfMaxChild(n: Node): Node {
+        return n.right?.let { r -> r.right?.let { findParentOfMaxChild(r) } ?: n }
+                ?: throw IllegalArgumentException("Right child must be non-null")
+
+    }
+
+    /**
+     * Remove a parent that has only one child.
+     * Removal is effectively is just coping the data from the child parent to the parent parent.
+     * @param parent Node to be deleted. Assume that it has just one child
+     * @param child Assume it is a child of the parent
+     */
+    private fun removeSingleChildNode(parent: Node, child: Node) {
+        parent.key = child.key
+        parent.left = child.left
+        parent.right = child.right
+    }
+
+    fun visit(): Array<Int> {
+        val a = left?.visit() ?: emptyArray()
+        val b = right?.visit() ?: emptyArray()
+        return a + arrayOf(key) + b
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/interfaces/ConflictingInterfaces.kt

@@ -0,0 +1,23 @@
+package com.baeldung.interfaces
+
+interface BaseInterface {
+    fun someMethod(): String
+}
+
+interface FirstChildInterface : BaseInterface {
+    override fun someMethod(): String {
+        return("Hello, from someMethod in FirstChildInterface")
+    }
+}
+
+interface SecondChildInterface : BaseInterface {
+    override fun someMethod(): String {
+        return("Hello, from someMethod in SecondChildInterface")
+    }
+}
+
+class ChildClass : FirstChildInterface, SecondChildInterface {
+    override fun someMethod(): String {
+        return super<SecondChildInterface>.someMethod()
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/interfaces/InterfaceDelegation.kt

@@ -0,0 +1,13 @@
+package com.baeldung.interfaces
+
+interface MyInterface {
+    fun someMethod(): String
+}
+
+class MyClass() : MyInterface {
+    override fun someMethod(): String {
+        return("Hello, World!")
+    }
+}
+
+class MyDerivedClass(myInterface: MyInterface) : MyInterface by myInterface

core-kotlin/src/main/kotlin/com/baeldung/interfaces/MultipleInterfaces.kt

@@ -0,0 +1,29 @@
+package com.baeldung.interfaces
+
+interface FirstInterface {	
+    fun someMethod(): String
+	
+    fun anotherMethod(): String {
+        return("Hello, from anotherMethod in FirstInterface")
+    }
+}
+
+interface SecondInterface {
+    fun someMethod(): String {
+        return("Hello, from someMethod in SecondInterface")
+    }
+	
+    fun anotherMethod(): String {
+        return("Hello, from anotherMethod in SecondInterface")
+    }
+}
+
+class SomeClass: FirstInterface, SecondInterface {	
+    override fun someMethod(): String {
+        return("Hello, from someMethod in SomeClass")
+    }
+	
+    override fun anotherMethod(): String {
+        return("Hello, from anotherMethod in SomeClass")
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/interfaces/SimpleInterface.kt

@@ -0,0 +1,24 @@
+package com.baeldung.interfaces
+
+interface SimpleInterface {
+    val firstProp: String
+    val secondProp: String
+        get() = "Second Property"
+    fun firstMethod(): String
+    fun secondMethod(): String {
+        println("Hello, from: " + secondProp)
+        return ""
+    }
+}
+
+class SimpleClass: SimpleInterface {
+    override val firstProp: String = "First Property"
+    override val secondProp: String
+        get() = "Second Property, Overridden!"
+    override fun firstMethod(): String {
+        return("Hello, from: " + firstProp)
+    }
+    override fun secondMethod(): String {
+        return("Hello, from: " + secondProp + firstProp)
+    }
+}

core-kotlin/src/test/kotlin/com/baeldung/datastructures/NodeTest.kt

@@ -0,0 +1,319 @@
+package com.baeldung.datastructures
+
+import org.junit.After
+import org.junit.Assert.*
+import org.junit.Before
+import org.junit.Test
+
+class NodeTest {
+
+    @Before
+    fun setUp() {
+    }
+
+    @After
+    fun tearDown() {
+    }
+
+    /**
+     * Test suit for finding the node by value
+     * Partition the tests as follows:
+     * 1. tree depth: 0, 1, > 1
+     * 2. pivot depth location: not present, 0, 1, 2, > 2
+     */
+
+    /**
+     * Find the node by value
+     * 1. tree depth: 0
+     * 2. pivot depth location: not present
+     */
+    @Test
+    fun givenDepthZero_whenPivotNotPresent_thenNull() {
+        val n = Node(1)
+        assertNull(n.find(2))
+    }
+
+    /**
+     * Find the node by value
+     * 1. tree depth: 0
+     * 2. pivot depth location: 0
+     */
+    @Test
+    fun givenDepthZero_whenPivotDepthZero_thenReturnNodeItself() {
+        val n = Node(1)
+        assertEquals(n, n.find(1))
+    }
+
+    /**
+     * Find the node by value
+     * 1. tree depth: 1
+     * 2. pivot depth location: not present
+     */
+    @Test
+    fun givenDepthOne_whenPivotNotPresent_thenNull() {
+        val n = Node(1, Node(0))
+        assertNull(n.find(2))
+    }
+
+    /**
+     * Find the node by value
+     * 1. tree depth: 1
+     * 2. pivot depth location: not present
+     */
+    @Test
+    fun givenDepthOne_whenPivotAtDepthOne_thenSuccess() {
+        val n = Node(1, Node(0))
+        assertEquals(n.left, n.find(0)
+        )
+    }
+
+    @Test
+    fun givenDepthTwo_whenPivotAtDepth2_then_Success() {
+        val left = Node(1, Node(0), Node(2))
+        val right = Node(5, Node(4), Node(6))
+        val n = Node(3, left, right)
+        assertEquals(left.left, n.find(0))
+    }
+
+
+    /**
+     * Test suit for inserting a value
+     * Partition the test as follows:
+     * 1. tree depth: 0, 1, 2, > 2
+     * 2. depth to insert: 0, 1, > 1
+     * 3. is duplicate: no, yes
+     * 4. sub-tree: left, right
+     */
+    /**
+     * Test for inserting a value
+     * 1. tree depth: 0
+     * 2. depth to insert: 1
+     * 3. is duplicate: no
+     * 4. sub-tree: right
+     */
+    @Test
+    fun givenTreeDepthZero_whenInsertNoDuplicateToRight_thenAddNode() {
+        val n = Node(1)
+        n.insert(2)
+        assertEquals(1, n.key)
+        with(n.right!!) {
+            assertEquals(2, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        assertNull(n.left)
+    }
+
+    /**
+     * Test for inserting a value
+     * 1. tree depth: 0
+     * 2. depth to insert: 1
+     * 3. is duplicate: no
+     * 4. sub-tree: right
+     */
+    @Test
+    fun givenTreeDepthZero_whenInsertNoDuplicateToLeft_thenSuccess() {
+        val n = Node(1)
+        n.insert(0)
+        assertEquals(1, n.key)
+        with(n.left!!) {
+            assertEquals(0, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        assertNull(n.right)
+    }
+
+    /**
+     * Test for inserting a value
+     * 1. tree depth: 0
+     * 2. depth to insert: 1
+     * 3. is duplicate: yes
+     */
+    @Test
+    fun givenTreeDepthZero_whenInsertDuplicate_thenSuccess() {
+        val n = Node(1)
+        n.insert(1)
+        assertEquals(1, n.key)
+        assertNull(n.right)
+        assertNull(n.left)
+    }
+
+
+    /**
+     * Test suit for inserting a value
+     * Partition the test as follows:
+     * 1. tree depth: 0, 1, 2, > 2
+     * 2. depth to insert: 0, 1, > 1
+     * 3. is duplicate: no, yes
+     * 4. sub-tree: left, right
+     */
+    /**
+     * Test for inserting a value
+     * 1. tree depth: 1
+     * 2. depth to insert: 1
+     * 3. is duplicate: no
+     * 4. sub-tree: right
+     */
+    @Test
+    fun givenTreeDepthOne_whenInsertNoDuplicateToRight_thenSuccess() {
+        val n = Node(10, Node(3))
+        n.insert(15)
+        assertEquals(10, n.key)
+        with(n.right!!) {
+            assertEquals(15, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        with(n.left!!) {
+            assertEquals(3, key)
+            assertNull(left)
+            assertNull(right)
+        }
+    }
+
+    /**
+     * Test for inserting a value
+     * 1. tree depth: 1
+     * 2. depth to insert: 1
+     * 3. is duplicate: no
+     * 4. sub-tree: left
+     */
+    @Test
+    fun givenTreeDepthOne_whenInsertNoDuplicateToLeft_thenAddNode() {
+        val n = Node(10, null, Node(15))
+        n.insert(3)
+        assertEquals(10, n.key)
+        with(n.right!!) {
+            assertEquals(15, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        with(n.left!!) {
+            assertEquals(3, key)
+            assertNull(left)
+            assertNull(right)
+        }
+    }
+
+    /**
+     * Test for inserting a value
+     * 1. tree depth: 1
+     * 2. depth to insert: 1
+     * 3. is duplicate: yes
+     */
+    @Test
+    fun givenTreeDepthOne_whenInsertDuplicate_thenNoChange() {
+        val n = Node(10, null, Node(15))
+        n.insert(15)
+        assertEquals(10, n.key)
+        with(n.right!!) {
+            assertEquals(15, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        assertNull(n.left)
+    }
+
+    /**
+     * Test suit for removal
+     * Partition the input as follows:
+     * 1. tree depth: 0, 1, 2, > 2
+     * 2. value to delete: absent, present
+     * 3. # child nodes: 0, 1, 2
+     */
+    /**
+     * Test for removal value
+     * 1. tree depth: 0
+     * 2. value to delete: absent
+     */
+    @Test
+    fun givenTreeDepthZero_whenValueAbsent_thenNoChange() {
+        val n = Node(1)
+        n.delete(0)
+        assertEquals(1, n.key)
+        assertNull(n.left)
+        assertNull(n.right)
+    }
+
+    /**
+     * Test for removal
+     * 1. tree depth: 1
+     * 2. value to delete: absent
+     */
+    @Test
+    fun givenTreeDepthOne_whenValueAbsent_thenNoChange() {
+        val n = Node(1, Node(0), Node(2))
+        n.delete(3)
+        assertEquals(1, n.key)
+        assertEquals(2, n.right!!.key)
+        with(n.left!!) {
+            assertEquals(0, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        with(n.right!!) {
+            assertNull(left)
+            assertNull(right)
+        }
+    }
+
+    /**
+     * Test suit for removal
+     * 1. tree depth: 1
+     * 2. value to delete:  present
+     * 3. # child nodes: 0
+     */
+    @Test
+    fun givenTreeDepthOne_whenNodeToDeleteHasNoChildren_thenChangeTree() {
+        val n = Node(1, Node(0))
+        n.delete(0)
+        assertEquals(1, n.key)
+        assertNull(n.left)
+        assertNull(n.right)
+    }
+
+    /**
+     * Test suit for removal
+     * 1. tree depth: 2
+     * 2. value to delete:  present
+     * 3. # child nodes: 1
+     */
+    @Test
+    fun givenTreeDepthTwo_whenNodeToDeleteHasOneChild_thenChangeTree() {
+        val n = Node(2, Node(0, null, Node(1)), Node(3))
+        n.delete(0)
+        assertEquals(2, n.key)
+        with(n.right!!) {
+            assertEquals(3, key)
+            assertNull(left)
+            assertNull(right)
+        }
+        with(n.left!!) {
+            assertEquals(1, key)
+            assertNull(left)
+            assertNull(right)
+        }
+    }
+
+    @Test
+    fun givenTreeDepthThree_whenNodeToDeleteHasTwoChildren_thenChangeTree() {
+        val l = Node(2, Node(1), Node(5, Node(4), Node(6)))
+        val r = Node(10, Node(9), Node(11))
+        val n = Node(8, l, r)
+        n.delete(8)
+        assertEquals(6, n.key)
+        with(n.left!!) {
+            assertEquals(2, key)
+            assertEquals(1, left!!.key)
+            assertEquals(5, right!!.key)
+            assertEquals(4, right!!.left!!.key)
+        }
+        with(n.right!!) {
+            assertEquals(10, key)
+            assertEquals(9, left!!.key)
+            assertEquals(11, right!!.key)
+        }
+    }
+
+}

core-kotlin/src/test/kotlin/com/baeldung/interfaces/InterfaceExamplesUnitTest.kt

@@ -0,0 +1,32 @@
+package com.baeldung.interfaces
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class InterfaceExamplesUnitTest {
+    @Test
+    fun givenAnInterface_whenImplemented_thenBehavesAsOverridden() {
+        val simpleClass = SimpleClass()
+        assertEquals("Hello, from: First Property", simpleClass.firstMethod())
+        assertEquals("Hello, from: Second Property, Overridden!First Property", simpleClass.secondMethod())
+    }
+
+    @Test
+    fun givenMultipleInterfaces_whenImplemented_thenBehavesAsOverridden() {
+        val someClass = SomeClass()
+        assertEquals("Hello, from someMethod in SomeClass", someClass.someMethod())
+        assertEquals("Hello, from anotherMethod in SomeClass", someClass.anotherMethod())
+    }
+
+    @Test
+    fun givenConflictingInterfaces_whenImplemented_thenBehavesAsOverridden() {
+        val childClass = ChildClass()
+        assertEquals("Hello, from someMethod in SecondChildInterface", childClass.someMethod())
+    }
+
+    @Test
+    fun givenAnInterface_whenImplemented_thenBehavesAsDelegated() {
+        val myClass = MyClass()
+        assertEquals("Hello, World!", MyDerivedClass(myClass).someMethod())
+    }
+}

gradle/junit5/build.gradle

@@ -0,0 +1,25 @@
+plugins {
+    // Apply the java-library plugin to add support for Java Library
+    id 'java-library'
+}
+
+dependencies {
+    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.3.1'
+    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.3.1'
+    
+    // Only necessary for JUnit 3 and 4 tests
+    testCompileOnly 'junit:junit:4.12' 
+    testRuntimeOnly 'org.junit.vintage:junit-vintage-engine:5.3.1' 
+    
+}
+
+repositories {
+    jcenter()
+}
+
+test {
+    useJUnitPlatform {
+    	includeTags 'fast'
+        excludeTags 'slow'
+    }
+}

gradle/junit5/src/test/java/com/example/CalculatorJUnit4Test.java

@@ -0,0 +1,12 @@
+package com.example;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class CalculatorJUnit4Test {
+    @Test
+    public void testAdd() {
+        assertEquals(42, Integer.sum(19, 23));
+    }
+}

gradle/junit5/src/test/java/com/example/CalculatorJUnit5Test.java

@@ -0,0 +1,36 @@
+package com.example;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;;
+
+public class CalculatorJUnit5Test {
+
+    @Tag("fast")
+    @Test
+    public void testAdd() {
+        assertEquals(42, Integer.sum(19, 23));
+    }
+
+    @Tag("slow")
+    @Test
+    public void testAddMaxInteger() {
+        assertEquals(2147483646, Integer.sum(2147183646, 300000));
+    }
+
+    @Tag("fast")
+    @Test
+    public void testAddZero() {
+        assertEquals(21, Integer.sum(21, 0));
+    }
+
+    @Tag("fast")
+    @Test
+    public void testDivide() {
+        assertThrows(ArithmeticException.class, () -> {
+            Integer.divideUnsigned(42, 0);
+        });
+    }
+}

gradle/settings.gradle

@@ -5,6 +5,6 @@ include 'greeting-library'
 include 'greeting-library-java'
 include 'greeter'
 include 'gradletaskdemo'
-
+include 'junit5'
 
 println 'This will be executed during the initialization phase.'

guava-collections/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear

guava-collections/README.md

@@ -0,0 +1,20 @@
+=========
+
+## Guava and Hamcrest Cookbooks and Examples
+
+
+### Relevant Articles: 
+- [Guava Collections Cookbook](http://www.baeldung.com/guava-collections)
+- [Guava Ordering Cookbook](http://www.baeldung.com/guava-order)
+- [Hamcrest Collections Cookbook](http://www.baeldung.com/hamcrest-collections-arrays)
+- [Partition a List in Java](http://www.baeldung.com/java-list-split)
+- [Filtering and Transforming Collections in Guava](http://www.baeldung.com/guava-filter-and-transform-a-collection)
+- [Guava – Join and Split Collections](http://www.baeldung.com/guava-joiner-and-splitter-tutorial)
+- [Guava – Lists](http://www.baeldung.com/guava-lists)
+- [Guava – Sets](http://www.baeldung.com/guava-sets)
+- [Guava – Maps](http://www.baeldung.com/guava-maps)
+- [Guide to Guava Multimap](http://www.baeldung.com/guava-multimap)
+- [Guide to Guava RangeSet](http://www.baeldung.com/guava-rangeset)
+- [Guide to Guava RangeMap](http://www.baeldung.com/guava-rangemap)
+- [Guide to Guava MinMaxPriorityQueue and EvictingQueue](http://www.baeldung.com/guava-minmax-priority-queue-and-evicting-queue)
+- [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)

guava-collections/pom.xml

@@ -0,0 +1,66 @@
+<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>guava-collections</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>guava-collections</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <!-- utils -->
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/org.hamcrest/java-hamcrest -->
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>java-hamcrest</artifactId>
+            <version>${java-hamcrest.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>guava</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <!-- util -->
+        <guava.version>24.0-jre</guava.version>
+        <commons-lang3.version>3.5</commons-lang3.version>
+        <commons-collections4.version>4.1</commons-collections4.version>
+
+        <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
+        <java-hamcrest.version>2.0.0.0</java-hamcrest.version>
+    </properties>
+
+</project>

guava-collections/src/main/resources/logback.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <logger name="org.springframework" level="WARN" />
+    <logger name="org.springframework.transaction" level="WARN" />
+
+    <!-- in order to debug some marshalling issues, this needs to be TRACE -->
+    <logger name="org.springframework.web.servlet.mvc" level="WARN" />
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

guava-collections/src/test/resources/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear

guava-collections/src/test/resources/test.out

@@ -0,0 +1 @@
+John Jane Adam Tom 

guava-collections/src/test/resources/test1.in

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

guava-collections/src/test/resources/test1_1.in

@@ -0,0 +1 @@
+Test

guava-collections/src/test/resources/test2.in

@@ -0,0 +1,4 @@
+John
+Jane
+Adam
+Tom

guava-collections/src/test/resources/test_copy.in

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

guava/README.md

@@ -4,33 +4,19 @@
 
 
 ### Relevant Articles: 
-- [Guava Collections Cookbook](http://www.baeldung.com/guava-collections)
-- [Guava Ordering Cookbook](http://www.baeldung.com/guava-order)
 - [Guava Functional Cookbook](http://www.baeldung.com/guava-functions-predicates)
-- [Hamcrest Collections Cookbook](http://www.baeldung.com/hamcrest-collections-arrays)
-- [Partition a List in Java](http://www.baeldung.com/java-list-split)
-- [Filtering and Transforming Collections in Guava](http://www.baeldung.com/guava-filter-and-transform-a-collection)
-- [Guava – Join and Split Collections](http://www.baeldung.com/guava-joiner-and-splitter-tutorial)
 - [Guava – Write to File, Read from File](http://www.baeldung.com/guava-write-to-file-read-from-file)
-- [Guava – Lists](http://www.baeldung.com/guava-lists)
-- [Guava – Sets](http://www.baeldung.com/guava-sets)
-- [Guava – Maps](http://www.baeldung.com/guava-maps)
 - [Guava Set + Function = Map](http://www.baeldung.com/guava-set-function-map-tutorial)
 - [Guide to Guava’s Ordering](http://www.baeldung.com/guava-ordering)
 - [Guide to Guava’s PreConditions](http://www.baeldung.com/guava-preconditions)
 - [Introduction to Guava CacheLoader](http://www.baeldung.com/guava-cacheloader)
 - [Introduction to Guava Memoizer](http://www.baeldung.com/guava-memoizer)
 - [Guide to Guava’s EventBus](http://www.baeldung.com/guava-eventbus)
-- [Guide to Guava Multimap](http://www.baeldung.com/guava-multimap)
-- [Guide to Guava RangeSet](http://www.baeldung.com/guava-rangeset)
-- [Guide to Guava RangeMap](http://www.baeldung.com/guava-rangemap)
 - [Guide to Guava Table](http://www.baeldung.com/guava-table)
 - [Guide to Guava’s Reflection Utilities](http://www.baeldung.com/guava-reflection)
 - [Guide to Guava ClassToInstanceMap](http://www.baeldung.com/guava-class-to-instance-map)
-- [Guide to Guava MinMaxPriorityQueue and EvictingQueue](http://www.baeldung.com/guava-minmax-priority-queue-and-evicting-queue)
 - [Guide to Mathematical Utilities in Guava](http://www.baeldung.com/guava-math)
 - [Bloom Filter in Java using Guava](http://www.baeldung.com/guava-bloom-filter)
 - [Using Guava CountingOutputStream](http://www.baeldung.com/guava-counting-outputstream)
 - [Hamcrest Text Matchers](http://www.baeldung.com/hamcrest-text-matchers)
 - [Quick Guide to the Guava RateLimiter](http://www.baeldung.com/guava-rate-limiter)
-- [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)

guava/pom.xml

@@ -14,12 +14,6 @@
     </parent>
 
     <dependencies>
-        <!-- utils -->
-        <dependency>
-            <groupId>org.apache.commons</groupId>
-            <artifactId>commons-collections4</artifactId>
-            <version>${commons-collections4.version}</version>
-        </dependency>
         <dependency>
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-lang3</artifactId>
@@ -56,7 +50,6 @@
         <!-- util -->
         <guava.version>24.0-jre</guava.version>
         <commons-lang3.version>3.5</commons-lang3.version>
-        <commons-collections4.version>4.1</commons-collections4.version>
 
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>

hibernate5/README.md

@@ -16,3 +16,4 @@
 - [Hibernate Entity Lifecycle](https://www.baeldung.com/hibernate-entity-lifecycle)
 - [Mapping A Hibernate Query to a Custom Class](https://www.baeldung.com/hibernate-query-to-custom-class)
 - [@JoinColumn Annotation Explained](https://www.baeldung.com/jpa-join-column)
+- [Hibernate 5 Naming Strategy Configuration](https://www.baeldung.com/hibernate-naming-strategy)

hibernate5/src/main/java/com/baeldung/hibernate/pojo/User.java

@@ -4,13 +4,23 @@ import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
 import javax.persistence.Id;
-import javax.persistence.SequenceGenerator;
+
+import org.hibernate.annotations.GenericGenerator;
+import org.hibernate.annotations.Parameter;
 
 @Entity
 public class User {
     @Id
-    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequence-generator")
+    @GeneratedValue(generator = "sequence-generator")
-    @SequenceGenerator(name = "sequence-generator", sequenceName = "user_sequence", initialValue = 4)
+    @GenericGenerator(
+        name = "sequence-generator",
+        strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator",
+        parameters = {
+                @Parameter(name = "sequence_name", value = "user_sequence"),
+                @Parameter(name = "initial_value", value = "4"),
+                @Parameter(name = "increment_size", value = "1")
+        }
+    )
     private long userId;
 
     public long getUserId() {

java-dates/pom.xml

@@ -80,7 +80,7 @@
         <joda-time.version>2.10</joda-time.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>
-		<maven.compiler.source>9</maven.compiler.source>
+		<maven.compiler.source>1.9</maven.compiler.source>
-        <maven.compiler.target>9</maven.compiler.target>
+        <maven.compiler.target>1.9</maven.compiler.target>
     </properties>
 </project>

java-dates/src/test/java/com/baeldung/date/DateDiffUnitTest.java

@@ -51,6 +51,15 @@ public class DateDiffUnitTest {
         assertEquals(diff, 6);
     }
 
+    @Test
+    public void givenTwoZonedDateTimesInJava8_whenDifferentiating_thenWeGetSix() {
+        LocalDateTime ldt = LocalDateTime.now();
+        ZonedDateTime now = ldt.atZone(ZoneId.of("America/Montreal"));
+        ZonedDateTime sixDaysBehind = now.withZoneSameInstant(ZoneId.of("Asia/Singapore")).minusDays(6);
+        long diff = ChronoUnit.DAYS.between(sixDaysBehind, now);
+        assertEquals(diff, 6);
+    }
+
     @Test
     public void givenTwoDatesInJodaTime_whenDifferentiating_thenWeGetSix() {
         org.joda.time.LocalDate now = org.joda.time.LocalDate.now();

java-dates/src/test/java/com/baeldung/datetime/DateTimeFormatterUnitTest.java

@@ -0,0 +1,158 @@
+package com.baeldung.datetime;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.time.LocalTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.time.format.FormatStyle;
+import java.time.temporal.ChronoUnit;
+import java.util.Locale;
+import java.util.TimeZone;
+
+public class DateTimeFormatterUnitTest {
+
+    @Test
+    public void givenDefaultUsLocaleAndDateTimeAndPattern_whenFormatWithDifferentLocales_thenGettingLocalizedDateTimes() {
+        Locale.setDefault(Locale.US);
+        LocalDateTime localDateTime = LocalDateTime.of(2018, 1, 1, 10, 15, 50, 500);
+        String pattern = "dd-MMMM-yyyy HH:mm:ss.SSS";
+
+        DateTimeFormatter defaultTimeFormatter = DateTimeFormatter.ofPattern(pattern);
+        DateTimeFormatter plTimeFormatter = DateTimeFormatter.ofPattern(pattern, new Locale("pl", "PL"));
+        DateTimeFormatter deTimeFormatter = DateTimeFormatter.ofPattern(pattern).withLocale(Locale.GERMANY);
+
+        Assert.assertEquals("01-January-2018 10:15:50.000", defaultTimeFormatter.format(localDateTime));
+        Assert.assertEquals("01-stycznia-2018 10:15:50.000", plTimeFormatter.format(localDateTime));
+        Assert.assertEquals("01-Januar-2018 10:15:50.000", deTimeFormatter.format(localDateTime));
+    }
+
+    @Test
+    public void givenDateTimeAndTimeZone_whenFormatWithDifferentLocales_thenGettingLocalizedZonedDateTimes() {
+        Locale.setDefault(Locale.US);
+        LocalDateTime localDateTime = LocalDateTime.of(2018, 1, 1, 10, 15, 50, 500);
+        ZoneId losAngelesTimeZone = TimeZone.getTimeZone("America/Los_Angeles").toZoneId();
+
+        DateTimeFormatter localizedFormatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL);
+        DateTimeFormatter frLocalizedFormatter =
+                DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).withLocale(Locale.FRANCE);
+        String formattedDateTime = localizedFormatter.format(ZonedDateTime.of(localDateTime, losAngelesTimeZone));
+        String frFormattedDateTime = frLocalizedFormatter.format(ZonedDateTime.of(localDateTime, losAngelesTimeZone));
+
+        Assert.assertEquals("Monday, January 1, 2018 10:15:50 AM PST", formattedDateTime);
+        Assert.assertEquals("lundi 1 janvier 2018 10 h 15 PST", frFormattedDateTime);
+    }
+
+    @Test
+    public void shouldPrintFormattedDate() {
+        String europeanDatePattern = "dd.MM.yyyy";
+        DateTimeFormatter europeanDateFormatter = DateTimeFormatter.ofPattern(europeanDatePattern);
+        LocalDate summerDay = LocalDate.of(2016, 7, 31);
+        Assert.assertEquals("31.07.2016", europeanDateFormatter.format(summerDay));
+    }
+
+    @Test
+    public void shouldPrintFormattedTime24() {
+        String timeColonPattern = "HH:mm:ss";
+        DateTimeFormatter timeColonFormatter = DateTimeFormatter.ofPattern(timeColonPattern);
+        LocalTime colonTime = LocalTime.of(17, 35, 50);
+        Assert.assertEquals("17:35:50", timeColonFormatter.format(colonTime));
+    }
+
+    @Test
+    public void shouldPrintFormattedTimeWithMillis() {
+        String timeColonPattern = "HH:mm:ss SSS";
+        DateTimeFormatter timeColonFormatter = DateTimeFormatter.ofPattern(timeColonPattern);
+        LocalTime colonTime = LocalTime.of(17, 35, 50).plus(329, ChronoUnit.MILLIS);
+        Assert.assertEquals("17:35:50 329", timeColonFormatter.format(colonTime));
+    }
+
+    @Test
+    public void shouldPrintFormattedTimePM() {
+        String timeColonPattern = "hh:mm:ss a";
+        DateTimeFormatter timeColonFormatter = DateTimeFormatter.ofPattern(timeColonPattern);
+        LocalTime colonTime = LocalTime.of(17, 35, 50);
+        Assert.assertEquals("05:35:50 PM", timeColonFormatter.format(colonTime));
+    }
+
+    @Test
+    public void shouldPrintFormattedUTCRelatedZonedDateTime() {
+        String newYorkDateTimePattern = "dd.MM.yyyy HH:mm z";
+        DateTimeFormatter newYorkDateFormatter = DateTimeFormatter.ofPattern(newYorkDateTimePattern);
+        LocalDateTime summerDay = LocalDateTime.of(2016, 7, 31, 14, 15);
+        Assert.assertEquals("31.07.2016 14:15 UTC-04:00", newYorkDateFormatter.format(ZonedDateTime.of(summerDay, ZoneId.of("UTC-4"))));
+    }
+
+    @Test
+    public void shouldPrintFormattedNewYorkZonedDateTime() {
+        String newYorkDateTimePattern = "dd.MM.yyyy HH:mm z";
+        DateTimeFormatter newYorkDateFormatter = DateTimeFormatter.ofPattern(newYorkDateTimePattern);
+        LocalDateTime summerDay = LocalDateTime.of(2016, 7, 31, 14, 15);
+        Assert.assertEquals("31.07.2016 14:15 EDT", newYorkDateFormatter.format(ZonedDateTime.of(summerDay, ZoneId.of("America/New_York"))));
+    }
+
+    @Test
+    public void shouldPrintStyledDate() {
+        LocalDate anotherSummerDay = LocalDate.of(2016, 8, 23);
+        Assert.assertEquals("Tuesday, August 23, 2016", DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL).format(anotherSummerDay));
+        Assert.assertEquals("August 23, 2016", DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG).format(anotherSummerDay));
+        Assert.assertEquals("Aug 23, 2016", DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).format(anotherSummerDay));
+        Assert.assertEquals("8/23/16", DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT).format(anotherSummerDay));
+    }
+
+    @Test
+    public void shouldPrintStyledDateTime() {
+        LocalDateTime anotherSummerDay = LocalDateTime.of(2016, 8, 23, 13, 12, 45);
+        Assert.assertEquals("Tuesday, August 23, 2016 1:12:45 PM EET", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+        Assert.assertEquals("August 23, 2016 1:12:45 PM EET", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+        Assert.assertEquals("Aug 23, 2016 1:12:45 PM", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+        Assert.assertEquals("8/23/16 1:12 PM", DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT).withZone(ZoneId.of("Europe/Helsinki")).format(anotherSummerDay));
+    }
+
+    @Test
+    public void shouldPrintFormattedDateTimeWithPredefined() {
+        Assert.assertEquals("2018-03-09", DateTimeFormatter.ISO_LOCAL_DATE.format(LocalDate.of(2018, 3, 9)));
+        Assert.assertEquals("2018-03-09-03:00", DateTimeFormatter.ISO_OFFSET_DATE.format(LocalDate.of(2018, 3, 9).atStartOfDay(ZoneId.of("UTC-3"))));
+        Assert.assertEquals("Fri, 9 Mar 2018 00:00:00 -0300", DateTimeFormatter.RFC_1123_DATE_TIME.format(LocalDate.of(2018, 3, 9).atStartOfDay(ZoneId.of("UTC-3"))));
+    }
+
+    @Test
+    public void shouldParseDateTime() {
+        Assert.assertEquals(LocalDate.of(2018, 3, 12), LocalDate.from(DateTimeFormatter.ISO_LOCAL_DATE.parse("2018-03-09")).plusDays(3));
+    }
+
+    @Test
+    public void shouldParseFormatStyleFull() {
+        ZonedDateTime dateTime = ZonedDateTime.from(DateTimeFormatter.ofLocalizedDateTime(FormatStyle.FULL).parse("Tuesday, August 23, 2016 1:12:45 PM EET"));
+        Assert.assertEquals(ZonedDateTime.of(LocalDateTime.of(2016, 8, 23, 22, 12, 45), ZoneId.of("Europe/Bucharest")), dateTime.plusHours(9));
+    }
+
+    @Test
+    public void shouldParseDateWithCustomFormatter() {
+        DateTimeFormatter europeanDateFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy");
+        Assert.assertFalse(LocalDate.from(europeanDateFormatter.parse("15.08.2014")).isLeapYear());
+    }
+
+    @Test
+    public void shouldParseTimeWithCustomFormatter() {
+        DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("hh:mm:ss a");
+        Assert.assertTrue(LocalTime.from(timeFormatter.parse("12:25:30 AM")).isBefore(LocalTime.NOON));
+    }
+
+    @Test
+    public void shouldParseZonedDateTimeWithCustomFormatter() {
+        DateTimeFormatter zonedFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm z");
+        Assert.assertEquals(7200, ZonedDateTime.from(zonedFormatter.parse("31.07.2016 14:15 GMT+02:00")).getOffset().getTotalSeconds());
+    }
+
+    @Test(expected = DateTimeParseException.class)
+    public void shouldExpectAnExceptionIfDateTimeStringNotMatchPattern() {
+        DateTimeFormatter zonedFormatter = DateTimeFormatter.ofPattern("dd.MM.yyyy HH:mm z");
+        ZonedDateTime.from(zonedFormatter.parse("31.07.2016 14:15"));
+    }
+}

java-dates/src/test/java/com/baeldung/zoneddatetime/ZonedDateTimeUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.zoneddatetime;
+
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
+import java.util.logging.Logger;
+
+import org.junit.Test;
+
+public class ZonedDateTimeUnitTest {
+
+    private static final Logger log = Logger.getLogger(ZonedDateTimeUnitTest.class.getName());
+
+    @Test
+    public void testZonedDateTimeToString() {
+
+        ZonedDateTime zonedDateTimeNow = ZonedDateTime.now(ZoneId.of("UTC"));
+        ZonedDateTime zonedDateTimeOf = ZonedDateTime.of(2018, 01, 01, 0, 0, 0, 0, ZoneId.of("UTC"));
+
+        LocalDateTime localDateTime = LocalDateTime.now();
+        ZonedDateTime zonedDateTime = ZonedDateTime.of(localDateTime, ZoneId.of("UTC"));
+
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM/dd/yyyy - hh:mm:ss Z");
+        String formattedString = zonedDateTime.format(formatter);
+
+        DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("MM/dd/yyyy - hh:mm:ss z");
+        String formattedString2 = zonedDateTime.format(formatter2);
+
+        log.info(formattedString);
+        log.info(formattedString2);
+
+    }
+
+    @Test
+    public void testZonedDateTimeFromString() {
+
+        ZonedDateTime zonedDateTime = ZonedDateTime.parse("2011-12-03T10:15:30+01:00", DateTimeFormatter.ISO_ZONED_DATE_TIME);
+
+        log.info(zonedDateTime.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));
+    }
+
+}

java-streams/README.md

@@ -13,3 +13,4 @@
 - [How to Iterate Over a Stream With Indices](http://www.baeldung.com/java-stream-indices)
 - [Primitive Type Streams in Java 8](http://www.baeldung.com/java-8-primitive-streams)
 - [Stream Ordering in Java](https://www.baeldung.com/java-stream-ordering)
+- [Introduction to Protonpack](https://www.baeldung.com/java-protonpack)

java-strings/README.md

@@ -31,3 +31,5 @@
 - [Converting a Stack Trace to a String in Java](https://www.baeldung.com/java-stacktrace-to-string)
 - [Sorting a String Alphabetically in Java](https://www.baeldung.com/java-sort-string-alphabetically)
 - [Remove Emojis from a Java String](https://www.baeldung.com/java-string-remove-emojis)
+- [String Not Empty Test Assertions in Java](https://www.baeldung.com/java-assert-string-not-empty)
+- [String Performance Hints](https://www.baeldung.com/java-string-performance)

javaxval/README.md

@@ -9,3 +9,4 @@ The "REST With Spring" Classes: http://bit.ly/restwithspring
 - [Java Bean Validation Basics](http://www.baeldung.com/javax-validation)
 - [Validating Container Elements with Bean Validation 2.0](http://www.baeldung.com/bean-validation-container-elements)
 - [Method Constraints with Bean Validation 2.0](http://www.baeldung.com/javax-validation-method-constraints)
+- [Difference Between @NotNull, @NotEmpty, and @NotBlank Constraints in Bean Validation](https://www.baeldung.com/java-bean-validation-not-null-empty-blank)

javaxval/pom.xml

@@ -33,7 +33,7 @@
             <version>${javax.el-api.version}</version>
         </dependency>
         <dependency>
-            <groupId>org.glassfish.web</groupId>
+            <groupId>org.glassfish</groupId>
             <artifactId>javax.el</artifactId>
             <version>${javax.el.version}</version>
         </dependency>

jee-7-security/README.md

@@ -0,0 +1,2 @@
+### Relevant Articles:
+- [Securing Java EE with Spring Security](http://www.baeldung.com/java-ee-spring-security)

jee-7-security/pom.xml

@@ -0,0 +1,102 @@
+<?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>jee-7-security</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>war</packaging>
+    <name>jee-7-security</name>
+    <description>JavaEE 7 Spring Security Application</description>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>javax</groupId>
+            <artifactId>javaee-api</artifactId>
+            <version>${javaee_api.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.sun.faces</groupId>
+            <artifactId>jsf-api</artifactId>
+            <version>${com.sun.faces.jsf.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.sun.faces</groupId>
+            <artifactId>jsf-impl</artifactId>
+            <version>${com.sun.faces.jsf.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.servlet</groupId>
+            <artifactId>jstl</artifactId>
+            <version>${jstl.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.servlet</groupId>
+            <artifactId>javax.servlet-api</artifactId>
+            <version>${javax.servlet-api.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.servlet.jsp</groupId>
+            <artifactId>jsp-api</artifactId>
+            <version>${jsp-api.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>taglibs</groupId>
+            <artifactId>standard</artifactId>
+            <version>${taglibs.standard.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>javax.mvc</groupId>
+            <artifactId>javax.mvc-api</artifactId>
+            <version>1.0-pr</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.security</groupId>
+            <artifactId>spring-security-web</artifactId>
+            <version>${org.springframework.security.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.security</groupId>
+            <artifactId>spring-security-config</artifactId>
+            <version>${org.springframework.security.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.security</groupId>
+            <artifactId>spring-security-taglibs</artifactId>
+            <version>${org.springframework.security.version}</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-war-plugin</artifactId>
+                <version>${maven-war-plugin.version}</version>
+                <configuration>
+                    <warSourceDirectory>src/main/webapp</warSourceDirectory>
+                    <failOnMissingWebXml>false</failOnMissingWebXml>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <javaee_api.version>7.0</javaee_api.version>
+        <com.sun.faces.jsf.version>2.2.14</com.sun.faces.jsf.version>
+        <jsp-api.version>2.2</jsp-api.version>
+        <taglibs.standard.version>1.1.2</taglibs.standard.version>
+        <org.springframework.security.version>4.2.3.RELEASE</org.springframework.security.version>
+    </properties>
+
+</project>

jee-7-security/src/main/java/com/baeldung/springsecurity/SecurityWebApplicationInitializer.java

@@ -1,4 +1,4 @@
-package com.baeldung.springSecurity;
+package com.baeldung.springsecurity;
 
 import org.springframework.security.web.context.AbstractSecurityWebApplicationInitializer;
 

jee-7-security/src/main/java/com/baeldung/springsecurity/SpringSecurityConfig.java

@@ -1,4 +1,4 @@
-package com.baeldung.springSecurity;
+package com.baeldung.springsecurity;
 
 import org.springframework.context.annotation.Configuration;
 import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;

jee-7-security/src/main/java/com/baeldung/springsecurity/controller/HomeController.java

@@ -1,4 +1,4 @@
-package com.baeldung.springSecurity.controller;
+package com.baeldung.springsecurity.controller;
 
 import javax.mvc.annotation.Controller;
 import javax.ws.rs.GET;

jee-7-security/src/main/java/com/baeldung/springsecurity/controller/LoginController.java

@@ -1,4 +1,4 @@
-package com.baeldung.springSecurity.controller;
+package com.baeldung.springsecurity.controller;
 
 import javax.mvc.annotation.Controller;
 import javax.ws.rs.GET;

jee-7-security/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="DEBUG">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

jee-7-security/src/main/webapp/WEB-INF/faces-config.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<faces-config
+    xmlns="http://java.sun.com/xml/ns/javaee"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
+    http://java.sun.com/xml/ns/javaee/web-facesconfig_2_0.xsd"
+    version="2.0">
+</faces-config>