Merge branch 'master' of https://github.com/eugenp/tutorials into public-access-modifier

algorithms-miscellaneous-3/README.md

@@ -1,4 +1,4 @@
-## Relevant articles:
+## Relevant Articles:
 
 - [Java Two Pointer Technique](https://www.baeldung.com/java-two-pointer-technique)
 - [Implementing Simple State Machines with Java Enums](https://www.baeldung.com/java-enum-simple-state-machine)

algorithms-miscellaneous-3/pom.xml

@@ -30,6 +30,30 @@
             <artifactId>guava</artifactId>
             <version>${guava.version}</version>
         </dependency>
+
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>retrofit</artifactId>
+            <version>${retrofit.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>converter-jackson</artifactId>
+            <version>${retrofit.version}</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>3.8.1</version>
+        </dependency>
+
+        <dependency>
+            <groupId>pl.pragmatists</groupId>
+            <artifactId>JUnitParams</artifactId>
+            <version>1.1.0</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -48,5 +72,6 @@
         <org.assertj.core.version>3.9.0</org.assertj.core.version>
         <commons-collections4.version>4.3</commons-collections4.version>
         <guava.version>28.0-jre</guava.version>
+        <retrofit.version>2.6.0</retrofit.version>
     </properties>
 </project>

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/interpolationsearch/InterpolationSearch.java

@@ -0,0 +1,35 @@
+package com.baeldung.algorithms.interpolationsearch;
+
+public class InterpolationSearch {
+
+    public static int interpolationSearch(int[] data, int item) {
+
+        int highEnd = (data.length - 1);
+        int lowEnd = 0;
+
+        while (item >= data[lowEnd] && item <= data[highEnd] && lowEnd <= highEnd) {
+
+            int probe = lowEnd + (highEnd - lowEnd) * (item - data[lowEnd]) / (data[highEnd] - data[lowEnd]);
+
+            if (highEnd == lowEnd) {
+                if (data[lowEnd] == item) {
+                    return lowEnd;
+                } else {
+                    return -1;
+                }
+            }
+
+            if (data[probe] == item) {
+                return probe;
+            }
+
+            if (data[probe] < item) {
+                lowEnd = probe + 1;
+            } else {
+                highEnd = probe - 1;
+            }
+        }
+        return -1;
+    }
+
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Centroid.java

@@ -0,0 +1,45 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Encapsulates all coordinates for a particular cluster centroid.
+ */
+public class Centroid {
+
+    /**
+     * The centroid coordinates.
+     */
+    private final Map<String, Double> coordinates;
+
+    public Centroid(Map<String, Double> coordinates) {
+        this.coordinates = coordinates;
+    }
+
+    public Map<String, Double> getCoordinates() {
+        return coordinates;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Centroid centroid = (Centroid) o;
+        return Objects.equals(getCoordinates(), centroid.getCoordinates());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getCoordinates());
+    }
+
+    @Override
+    public String toString() {
+        return "Centroid " + coordinates;
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Distance.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+
+/**
+ * Defines a contract to calculate distance between two feature vectors. The less the
+ * calculated distance, the more two items are similar to each other.
+ */
+public interface Distance {
+
+    /**
+     * Calculates the distance between two feature vectors.
+     *
+     * @param f1 The first set of features.
+     * @param f2 The second set of features.
+     * @return Calculated distance.
+     * @throws IllegalArgumentException If the given feature vectors are invalid.
+     */
+    double calculate(Map<String, Double> f1, Map<String, Double> f2);
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Errors.java

@@ -0,0 +1,23 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Encapsulates methods to calculates errors between centroid and the cluster members.
+ */
+public class Errors {
+
+    public static double sse(Map<Centroid, List<Record>> clustered, Distance distance) {
+        double sum = 0;
+        for (Map.Entry<Centroid, List<Record>> entry : clustered.entrySet()) {
+            Centroid centroid = entry.getKey();
+            for (Record record : entry.getValue()) {
+                double d = distance.calculate(centroid.getCoordinates(), record.getFeatures());
+                sum += Math.pow(d, 2);
+            }
+        }
+
+        return sum;
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/EuclideanDistance.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+
+/**
+ * Calculates the distance between two items using the Euclidean formula.
+ */
+public class EuclideanDistance implements Distance {
+
+    @Override
+    public double calculate(Map<String, Double> f1, Map<String, Double> f2) {
+        if (f1 == null || f2 == null) {
+            throw new IllegalArgumentException("Feature vectors can't be null");
+        }
+
+        double sum = 0;
+        for (String key : f1.keySet()) {
+            Double v1 = f1.get(key);
+            Double v2 = f2.get(key);
+
+            if (v1 != null && v2 != null) sum += Math.pow(v1 - v2, 2);
+        }
+
+        return Math.sqrt(sum);
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/KMeans.java

@@ -0,0 +1,236 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.Set;
+
+import static java.util.stream.Collectors.toList;
+import static java.util.stream.Collectors.toSet;
+
+/**
+ * Encapsulates an implementation of KMeans clustering algorithm.
+ *
+ * @author Ali Dehghani
+ */
+public class KMeans {
+
+    private KMeans() {
+        throw new IllegalAccessError("You shouldn't call this constructor");
+    }
+
+    /**
+     * Will be used to generate random numbers.
+     */
+    private static final Random random = new Random();
+
+    /**
+     * Performs the K-Means clustering algorithm on the given dataset.
+     *
+     * @param records       The dataset.
+     * @param k             Number of Clusters.
+     * @param distance      To calculate the distance between two items.
+     * @param maxIterations Upper bound for the number of iterations.
+     * @return K clusters along with their features.
+     */
+    public static Map<Centroid, List<Record>> fit(List<Record> records, int k, Distance distance, int maxIterations) {
+        applyPreconditions(records, k, distance, maxIterations);
+
+        List<Centroid> centroids = randomCentroids(records, k);
+        Map<Centroid, List<Record>> clusters = new HashMap<>();
+        Map<Centroid, List<Record>> lastState = new HashMap<>();
+
+        // iterate for a pre-defined number of times
+        for (int i = 0; i < maxIterations; i++) {
+            boolean isLastIteration = i == maxIterations - 1;
+
+            // in each iteration we should find the nearest centroid for each record
+            for (Record record : records) {
+                Centroid centroid = nearestCentroid(record, centroids, distance);
+                assignToCluster(clusters, record, centroid);
+            }
+
+            // if the assignment does not change, then the algorithm terminates
+            boolean shouldTerminate = isLastIteration || clusters.equals(lastState);
+            lastState = clusters;
+            if (shouldTerminate) {
+                break;
+            }
+
+            // at the end of each iteration we should relocate the centroids
+            centroids = relocateCentroids(clusters);
+            clusters = new HashMap<>();
+        }
+
+        return lastState;
+    }
+
+    /**
+     * Move all cluster centroids to the average of all assigned features.
+     *
+     * @param clusters The current cluster configuration.
+     * @return Collection of new and relocated centroids.
+     */
+    private static List<Centroid> relocateCentroids(Map<Centroid, List<Record>> clusters) {
+        return clusters
+          .entrySet()
+          .stream()
+          .map(e -> average(e.getKey(), e.getValue()))
+          .collect(toList());
+    }
+
+    /**
+     * Moves the given centroid to the average position of all assigned features. If
+     * the centroid has no feature in its cluster, then there would be no need for a
+     * relocation. Otherwise, for each entry we calculate the average of all records
+     * first by summing all the entries and then dividing the final summation value by
+     * the number of records.
+     *
+     * @param centroid The centroid to move.
+     * @param records  The assigned features.
+     * @return The moved centroid.
+     */
+    private static Centroid average(Centroid centroid, List<Record> records) {
+        // if this cluster is empty, then we shouldn't move the centroid
+        if (records == null || records.isEmpty()) {
+            return centroid;
+        }
+
+        // Since some records don't have all possible attributes, we initialize
+        // average coordinates equal to current centroid coordinates
+        Map<String, Double> average = centroid.getCoordinates();
+
+        // The average function works correctly if we clear all coordinates corresponding
+        // to present record attributes
+        records
+          .stream()
+          .flatMap(e -> e
+            .getFeatures()
+            .keySet()
+            .stream())
+          .forEach(k -> average.put(k, 0.0));
+
+        for (Record record : records) {
+            record
+              .getFeatures()
+              .forEach((k, v) -> average.compute(k, (k1, currentValue) -> v + currentValue));
+        }
+
+        average.forEach((k, v) -> average.put(k, v / records.size()));
+
+        return new Centroid(average);
+    }
+
+    /**
+     * Assigns a feature vector to the given centroid. If this is the first assignment for this centroid,
+     * first we should create the list.
+     *
+     * @param clusters The current cluster configuration.
+     * @param record   The feature vector.
+     * @param centroid The centroid.
+     */
+    private static void assignToCluster(Map<Centroid, List<Record>> clusters, Record record, Centroid centroid) {
+        clusters.compute(centroid, (key, list) -> {
+            if (list == null) {
+                list = new ArrayList<>();
+            }
+
+            list.add(record);
+            return list;
+        });
+    }
+
+    /**
+     * With the help of the given distance calculator, iterates through centroids and finds the
+     * nearest one to the given record.
+     *
+     * @param record    The feature vector to find a centroid for.
+     * @param centroids Collection of all centroids.
+     * @param distance  To calculate the distance between two items.
+     * @return The nearest centroid to the given feature vector.
+     */
+    private static Centroid nearestCentroid(Record record, List<Centroid> centroids, Distance distance) {
+        double minimumDistance = Double.MAX_VALUE;
+        Centroid nearest = null;
+
+        for (Centroid centroid : centroids) {
+            double currentDistance = distance.calculate(record.getFeatures(), centroid.getCoordinates());
+
+            if (currentDistance < minimumDistance) {
+                minimumDistance = currentDistance;
+                nearest = centroid;
+            }
+        }
+
+        return nearest;
+    }
+
+    /**
+     * Generates k random centroids. Before kicking-off the centroid generation process,
+     * first we calculate the possible value range for each attribute. Then when
+     * we're going to generate the centroids, we generate random coordinates in
+     * the [min, max] range for each attribute.
+     *
+     * @param records The dataset which helps to calculate the [min, max] range for
+     *                each attribute.
+     * @param k       Number of clusters.
+     * @return Collections of randomly generated centroids.
+     */
+    private static List<Centroid> randomCentroids(List<Record> records, int k) {
+        List<Centroid> centroids = new ArrayList<>();
+        Map<String, Double> maxs = new HashMap<>();
+        Map<String, Double> mins = new HashMap<>();
+
+        for (Record record : records) {
+            record
+              .getFeatures()
+              .forEach((key, value) -> {
+                  // compares the value with the current max and choose the bigger value between them
+                  maxs.compute(key, (k1, max) -> max == null || value > max ? value : max);
+
+                  // compare the value with the current min and choose the smaller value between them
+                  mins.compute(key, (k1, min) -> min == null || value < min ? value : min);
+              });
+        }
+
+        Set<String> attributes = records
+          .stream()
+          .flatMap(e -> e
+            .getFeatures()
+            .keySet()
+            .stream())
+          .collect(toSet());
+        for (int i = 0; i < k; i++) {
+            Map<String, Double> coordinates = new HashMap<>();
+            for (String attribute : attributes) {
+                double max = maxs.get(attribute);
+                double min = mins.get(attribute);
+                coordinates.put(attribute, random.nextDouble() * (max - min) + min);
+            }
+
+            centroids.add(new Centroid(coordinates));
+        }
+
+        return centroids;
+    }
+
+    private static void applyPreconditions(List<Record> records, int k, Distance distance, int maxIterations) {
+        if (records == null || records.isEmpty()) {
+            throw new IllegalArgumentException("The dataset can't be empty");
+        }
+
+        if (k <= 1) {
+            throw new IllegalArgumentException("It doesn't make sense to have less than or equal to 1 cluster");
+        }
+
+        if (distance == null) {
+            throw new IllegalArgumentException("The distance calculator is required");
+        }
+
+        if (maxIterations <= 0) {
+            throw new IllegalArgumentException("Max iterations should be a positive number");
+        }
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/LastFm.java

@@ -0,0 +1,144 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import okhttp3.OkHttpClient;
+import retrofit2.Retrofit;
+import retrofit2.converter.jackson.JacksonConverterFactory;
+
+import static java.util.stream.Collectors.toSet;
+
+public class LastFm {
+
+    private static OkHttpClient okHttp = new OkHttpClient.Builder()
+      .addInterceptor(new LastFmService.Authenticator("put your API key here"))
+      .build();
+
+    private static Retrofit retrofit = new Retrofit.Builder()
+      .client(okHttp)
+      .addConverterFactory(JacksonConverterFactory.create())
+      .baseUrl("http://ws.audioscrobbler.com/")
+      .build();
+
+    private static LastFmService lastFm = retrofit.create(LastFmService.class);
+
+    private static ObjectMapper mapper = new ObjectMapper();
+
+    public static void main(String[] args) throws IOException {
+        List<String> artists = getTop100Artists();
+        Set<String> tags = getTop100Tags();
+        List<Record> records = datasetWithTaggedArtists(artists, tags);
+
+        Map<Centroid, List<Record>> clusters = KMeans.fit(records, 7, new EuclideanDistance(), 1000);
+        // Print the cluster configuration
+        clusters.forEach((key, value) -> {
+            System.out.println("------------------------------ CLUSTER -----------------------------------");
+
+            System.out.println(sortedCentroid(key));
+            String members = String.join(", ", value
+              .stream()
+              .map(Record::getDescription)
+              .collect(toSet()));
+            System.out.print(members);
+
+            System.out.println();
+            System.out.println();
+        });
+
+        Map<String, Object> json = convertToD3CompatibleMap(clusters);
+        System.out.println(mapper.writeValueAsString(json));
+    }
+
+    private static Map<String, Object> convertToD3CompatibleMap(Map<Centroid, List<Record>> clusters) {
+        Map<String, Object> json = new HashMap<>();
+        json.put("name", "Musicians");
+        List<Map<String, Object>> children = new ArrayList<>();
+        clusters.forEach((key, value) -> {
+            Map<String, Object> child = new HashMap<>();
+            child.put("name", dominantGenre(sortedCentroid(key)));
+            List<Map<String, String>> nested = new ArrayList<>();
+            for (Record record : value) {
+                nested.add(Collections.singletonMap("name", record.getDescription()));
+            }
+            child.put("children", nested);
+
+            children.add(child);
+        });
+        json.put("children", children);
+        return json;
+    }
+
+    private static String dominantGenre(Centroid centroid) {
+        return centroid
+          .getCoordinates()
+          .keySet()
+          .stream()
+          .limit(2)
+          .collect(Collectors.joining(", "));
+    }
+
+    private static Centroid sortedCentroid(Centroid key) {
+        List<Map.Entry<String, Double>> entries = new ArrayList<>(key
+          .getCoordinates()
+          .entrySet());
+        entries.sort((e1, e2) -> e2
+          .getValue()
+          .compareTo(e1.getValue()));
+
+        Map<String, Double> sorted = new LinkedHashMap<>();
+        for (Map.Entry<String, Double> entry : entries) {
+            sorted.put(entry.getKey(), entry.getValue());
+        }
+
+        return new Centroid(sorted);
+    }
+
+    private static List<Record> datasetWithTaggedArtists(List<String> artists, Set<String> topTags) throws IOException {
+        List<Record> records = new ArrayList<>();
+        for (String artist : artists) {
+            Map<String, Double> tags = lastFm
+              .topTagsFor(artist)
+              .execute()
+              .body()
+              .all();
+
+            // Only keep popular tags.
+            tags
+              .entrySet()
+              .removeIf(e -> !topTags.contains(e.getKey()));
+
+            records.add(new Record(artist, tags));
+        }
+        return records;
+    }
+
+    private static Set<String> getTop100Tags() throws IOException {
+        return lastFm
+          .topTags()
+          .execute()
+          .body()
+          .all();
+    }
+
+    private static List<String> getTop100Artists() throws IOException {
+        List<String> artists = new ArrayList<>();
+        for (int i = 1; i <= 2; i++) {
+            artists.addAll(lastFm
+              .topArtists(i)
+              .execute()
+              .body()
+              .all());
+        }
+
+        return artists;
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/LastFmService.java

@@ -0,0 +1,118 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import okhttp3.HttpUrl;
+import okhttp3.Interceptor;
+import okhttp3.Request;
+import okhttp3.Response;
+import retrofit2.Call;
+import retrofit2.http.GET;
+import retrofit2.http.Query;
+
+import static com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.ANY;
+import static java.util.stream.Collectors.toList;
+
+public interface LastFmService {
+
+    @GET("/2.0/?method=chart.gettopartists&format=json&limit=50")
+    Call<Artists> topArtists(@Query("page") int page);
+
+    @GET("/2.0/?method=artist.gettoptags&format=json&limit=20&autocorrect=1")
+    Call<Tags> topTagsFor(@Query("artist") String artist);
+
+    @GET("/2.0/?method=chart.gettoptags&format=json&limit=100")
+    Call<TopTags> topTags();
+
+    /**
+     * HTTP interceptor to intercept all HTTP requests and add the API key to them.
+     */
+    class Authenticator implements Interceptor {
+
+        private final String apiKey;
+
+        Authenticator(String apiKey) {
+            this.apiKey = apiKey;
+        }
+
+        @Override
+        public Response intercept(Chain chain) throws IOException {
+            HttpUrl url = chain
+              .request()
+              .url()
+              .newBuilder()
+              .addQueryParameter("api_key", apiKey)
+              .build();
+            Request request = chain
+              .request()
+              .newBuilder()
+              .url(url)
+              .build();
+
+            return chain.proceed(request);
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class TopTags {
+
+        private Map<String, Object> tags;
+
+        @SuppressWarnings("unchecked")
+        public Set<String> all() {
+            List<Map<String, Object>> topTags = (List<Map<String, Object>>) tags.get("tag");
+            return topTags
+              .stream()
+              .map(e -> ((String) e.get("name")))
+              .collect(Collectors.toSet());
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class Tags {
+
+        @JsonProperty("toptags") private Map<String, Object> topTags;
+
+        @SuppressWarnings("unchecked")
+        public Map<String, Double> all() {
+            try {
+                Map<String, Double> all = new HashMap<>();
+                List<Map<String, Object>> tags = (List<Map<String, Object>>) topTags.get("tag");
+                for (Map<String, Object> tag : tags) {
+                    all.put(((String) tag.get("name")), ((Integer) tag.get("count")).doubleValue());
+                }
+
+                return all;
+            } catch (Exception e) {
+                return Collections.emptyMap();
+            }
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class Artists {
+
+        private Map<String, Object> artists;
+
+        @SuppressWarnings("unchecked")
+        public List<String> all() {
+            try {
+                List<Map<String, Object>> artists = (List<Map<String, Object>>) this.artists.get("artist");
+                return artists
+                  .stream()
+                  .map(e -> ((String) e.get("name")))
+                  .collect(toList());
+            } catch (Exception e) {
+                return Collections.emptyList();
+            }
+        }
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Record.java

@@ -0,0 +1,65 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Encapsulates all feature values for a few attributes. Optionally each record
+ * can be described with the {@link #description} field.
+ */
+public class Record {
+
+    /**
+     * The record description. For example, this can be the artist name for the famous musician
+     * example.
+     */
+    private final String description;
+
+    /**
+     * Encapsulates all attributes and their corresponding values, i.e. features.
+     */
+    private final Map<String, Double> features;
+
+    public Record(String description, Map<String, Double> features) {
+        this.description = description;
+        this.features = features;
+    }
+
+    public Record(Map<String, Double> features) {
+        this("", features);
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public Map<String, Double> getFeatures() {
+        return features;
+    }
+
+    @Override
+    public String toString() {
+        String prefix = description == null || description
+          .trim()
+          .isEmpty() ? "Record" : description;
+
+        return prefix + ": " + features;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Record record = (Record) o;
+        return Objects.equals(getDescription(), record.getDescription()) && Objects.equals(getFeatures(), record.getFeatures());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getDescription(), getFeatures());
+    }
+}

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/printtriangles/PrintTriangleExamples.java

@@ -0,0 +1,49 @@
+package com.baeldung.algorithms.printtriangles;
+
+import org.apache.commons.lang3.StringUtils;
+
+public class PrintTriangleExamples {
+
+    public static String printARightAngledTriangle(int N) {
+        StringBuilder result = new StringBuilder();
+        for (int r = 1; r <= N; r++) {
+            for (int j = 1; j <= r; j++) {
+                result.append("*");
+            }
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static String printAnIsoscelesTriangle(int N) {
+        StringBuilder result = new StringBuilder();
+        for (int r = 1; r <= N; r++) {
+            for (int sp = 1; sp <= N - r; sp++) {
+                result.append(" ");
+            }
+            for (int c = 1; c <= (r * 2) - 1; c++) {
+                result.append("*");
+            }
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static String printAnIsoscelesTriangleUsingSubstring(int N) {
+        StringBuilder result = new StringBuilder();
+        String helperString = StringUtils.repeat(' ', N - 1) + StringUtils.repeat('*', N * 2 - 1);
+
+        for (int r = 0; r < N; r++) {
+            result.append(helperString.substring(r, N + 2 * r));
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static void main(String[] args) {
+        System.out.println(printARightAngledTriangle(5));
+        System.out.println(printAnIsoscelesTriangle(5));
+        System.out.println(printAnIsoscelesTriangleUsingSubstring(5));
+    }
+
+}

algorithms-miscellaneous-3/src/main/resources/kmeans/lastfm.json

@@ -0,0 +1,490 @@
+{
+  "children": [
+    {
+      "children": [
+        {
+          "name": "Radiohead"
+        },
+        {
+          "name": "Red Hot Chili Peppers"
+        },
+        {
+          "name": "Coldplay"
+        },
+        {
+          "name": "Nirvana"
+        },
+        {
+          "name": "Panic! at the Disco"
+        },
+        {
+          "name": "The Cure"
+        },
+        {
+          "name": "Linkin Park"
+        },
+        {
+          "name": "Radiohead"
+        },
+        {
+          "name": "Red Hot Chili Peppers"
+        },
+        {
+          "name": "Coldplay"
+        },
+        {
+          "name": "Nirvana"
+        },
+        {
+          "name": "Panic! at the Disco"
+        },
+        {
+          "name": "The Cure"
+        },
+        {
+          "name": "Linkin Park"
+        },
+        {
+          "name": "Muse"
+        },
+        {
+          "name": "Maroon 5"
+        },
+        {
+          "name": "Foo Fighters"
+        },
+        {
+          "name": "Paramore"
+        },
+        {
+          "name": "Oasis"
+        },
+        {
+          "name": "Fall Out Boy"
+        },
+        {
+          "name": "OneRepublic"
+        },
+        {
+          "name": "Weezer"
+        },
+        {
+          "name": "System of a Down"
+        },
+        {
+          "name": "The White Stripes"
+        }
+      ],
+      "name": "rock, alternative"
+    },
+    {
+      "children": [
+        {
+          "name": "Lil Nas X"
+        },
+        {
+          "name": "Post Malone"
+        },
+        {
+          "name": "Drake"
+        },
+        {
+          "name": "Kanye West"
+        },
+        {
+          "name": "Kendrick Lamar"
+        },
+        {
+          "name": "Tyler, the Creator"
+        },
+        {
+          "name": "Eminem"
+        },
+        {
+          "name": "Childish Gambino"
+        },
+        {
+          "name": "Frank Ocean"
+        },
+        {
+          "name": "Lil Nas X"
+        },
+        {
+          "name": "Post Malone"
+        },
+        {
+          "name": "Drake"
+        },
+        {
+          "name": "Kanye West"
+        },
+        {
+          "name": "Kendrick Lamar"
+        },
+        {
+          "name": "Tyler, the Creator"
+        },
+        {
+          "name": "Eminem"
+        },
+        {
+          "name": "Childish Gambino"
+        },
+        {
+          "name": "Frank Ocean"
+        },
+        {
+          "name": "Lizzo"
+        },
+        {
+          "name": "Travi$ Scott"
+        },
+        {
+          "name": "A$AP Rocky"
+        },
+        {
+          "name": "Nicki Minaj"
+        },
+        {
+          "name": "xxxtentacion"
+        }
+      ],
+      "name": "Hip-Hop, rap"
+    },
+    {
+      "children": [
+        {
+          "name": "Arctic Monkeys"
+        },
+        {
+          "name": "Imagine Dragons"
+        },
+        {
+          "name": "The Killers"
+        },
+        {
+          "name": "Gorillaz"
+        },
+        {
+          "name": "The Black Keys"
+        },
+        {
+          "name": "Arctic Monkeys"
+        },
+        {
+          "name": "Imagine Dragons"
+        },
+        {
+          "name": "The Killers"
+        },
+        {
+          "name": "Gorillaz"
+        },
+        {
+          "name": "The Black Keys"
+        },
+        {
+          "name": "Twenty One Pilots"
+        },
+        {
+          "name": "Ellie Goulding"
+        },
+        {
+          "name": "Florence + the Machine"
+        },
+        {
+          "name": "Vampire Weekend"
+        },
+        {
+          "name": "The Smiths"
+        },
+        {
+          "name": "The Strokes"
+        },
+        {
+          "name": "MGMT"
+        },
+        {
+          "name": "Foster the People"
+        },
+        {
+          "name": "Two Door Cinema Club"
+        },
+        {
+          "name": "Cage the Elephant"
+        },
+        {
+          "name": "Arcade Fire"
+        },
+        {
+          "name": "The 1975"
+        }
+      ],
+      "name": "indie, alternative"
+    },
+    {
+      "children": [
+        {
+          "name": "Ed Sheeran"
+        },
+        {
+          "name": "Tame Impala"
+        },
+        {
+          "name": "Ed Sheeran"
+        },
+        {
+          "name": "Tame Impala"
+        },
+        {
+          "name": "Green Day"
+        },
+        {
+          "name": "Metallica"
+        },
+        {
+          "name": "blink-182"
+        },
+        {
+          "name": "Bon Iver"
+        },
+        {
+          "name": "The Clash"
+        }
+      ],
+      "name": "rock, punk rock"
+    },
+    {
+      "children": [
+        {
+          "name": "Calvin Harris"
+        },
+        {
+          "name": "The Weeknd"
+        },
+        {
+          "name": "The Chainsmokers"
+        },
+        {
+          "name": "Daft Punk"
+        },
+        {
+          "name": "Marshmello"
+        },
+        {
+          "name": "David Guetta"
+        },
+        {
+          "name": "Calvin Harris"
+        },
+        {
+          "name": "The Weeknd"
+        },
+        {
+          "name": "The Chainsmokers"
+        },
+        {
+          "name": "Daft Punk"
+        },
+        {
+          "name": "Marshmello"
+        },
+        {
+          "name": "David Guetta"
+        },
+        {
+          "name": "Avicii"
+        },
+        {
+          "name": "Kygo"
+        },
+        {
+          "name": "Martin Garrix"
+        },
+        {
+          "name": "Major Lazer"
+        },
+        {
+          "name": "Depeche Mode"
+        }
+      ],
+      "name": "electronic, dance"
+    },
+    {
+      "children": [
+        {
+          "name": "Queen"
+        },
+        {
+          "name": "The Beatles"
+        },
+        {
+          "name": "David Bowie"
+        },
+        {
+          "name": "Fleetwood Mac"
+        },
+        {
+          "name": "Pink Floyd"
+        },
+        {
+          "name": "The Rolling Stones"
+        },
+        {
+          "name": "Led Zeppelin"
+        },
+        {
+          "name": "Queen"
+        },
+        {
+          "name": "The Beatles"
+        },
+        {
+          "name": "David Bowie"
+        },
+        {
+          "name": "Fleetwood Mac"
+        },
+        {
+          "name": "Pink Floyd"
+        },
+        {
+          "name": "The Rolling Stones"
+        },
+        {
+          "name": "Led Zeppelin"
+        },
+        {
+          "name": "Elton John"
+        }
+      ],
+      "name": "classic rock, rock"
+    },
+    {
+      "children": [
+        {
+          "name": "Billie Eilish"
+        },
+        {
+          "name": "Ariana Grande"
+        },
+        {
+          "name": "Taylor Swift"
+        },
+        {
+          "name": "Beyoncé"
+        },
+        {
+          "name": "Shawn Mendes"
+        },
+        {
+          "name": "Rihanna"
+        },
+        {
+          "name": "Lana Del Rey"
+        },
+        {
+          "name": "Katy Perry"
+        },
+        {
+          "name": "Lady Gaga"
+        },
+        {
+          "name": "Miley Cyrus"
+        },
+        {
+          "name": "Mark Ronson"
+        },
+        {
+          "name": "Madonna"
+        },
+        {
+          "name": "Lorde"
+        },
+        {
+          "name": "Khalid"
+        },
+        {
+          "name": "Billie Eilish"
+        },
+        {
+          "name": "Ariana Grande"
+        },
+        {
+          "name": "Taylor Swift"
+        },
+        {
+          "name": "Beyoncé"
+        },
+        {
+          "name": "Shawn Mendes"
+        },
+        {
+          "name": "Rihanna"
+        },
+        {
+          "name": "Lana Del Rey"
+        },
+        {
+          "name": "Katy Perry"
+        },
+        {
+          "name": "Lady Gaga"
+        },
+        {
+          "name": "Miley Cyrus"
+        },
+        {
+          "name": "Mark Ronson"
+        },
+        {
+          "name": "Madonna"
+        },
+        {
+          "name": "Lorde"
+        },
+        {
+          "name": "Khalid"
+        },
+        {
+          "name": "Sia"
+        },
+        {
+          "name": "Sam Smith"
+        },
+        {
+          "name": "Halsey"
+        },
+        {
+          "name": "Michael Jackson"
+        },
+        {
+          "name": "Charli XCX"
+        },
+        {
+          "name": "Britney Spears"
+        },
+        {
+          "name": "Dua Lipa"
+        },
+        {
+          "name": "Jonas Brothers"
+        },
+        {
+          "name": "Bruno Mars"
+        },
+        {
+          "name": "Carly Rae Jepsen"
+        },
+        {
+          "name": "P!nk"
+        },
+        {
+          "name": "Adele"
+        }
+      ],
+      "name": "pop, female vocalists"
+    }
+  ],
+  "name": "Musicians"
+}

algorithms-miscellaneous-3/src/main/resources/kmeans/radial.html

@@ -0,0 +1,68 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<style>
+    .node circle {
+        fill: #fff;
+        stroke: steelblue;
+        stroke-width: 1.5px;
+    }
+
+    .node {
+        font: 10px sans-serif;
+    }
+
+    .link {
+        fill: none;
+        stroke: #ccc;
+        stroke-width: 1.5px;
+    }
+</style>
+<body>
+<script src="http://d3js.org/d3.v3.min.js"></script>
+<script>
+    var diameter = 1100;
+    var tree = d3.layout.tree()
+        .size([360, diameter / 2 - 300])
+        .separation(function (a, b) {
+            return (a.parent == b.parent ? 1 : 2) / a.depth;
+        });
+    var diagonal = d3.svg.diagonal.radial()
+        .projection(function (d) {
+            return [d.y, d.x / 180 * Math.PI];
+        });
+    var svg = d3.select("body").append("svg")
+        .attr("width", diameter)
+        .attr("height", diameter - 150)
+        .append("g")
+        .attr("transform", "translate(" + diameter / 2 + "," + diameter / 2 + ")");
+    d3.json("lastfm.json", function (error, root) {
+        var nodes = tree.nodes(root),
+            links = tree.links(nodes);
+        var link = svg.selectAll(".link")
+            .data(links)
+            .enter().append("path")
+            .attr("class", "link")
+            .attr("d", diagonal);
+        var node = svg.selectAll(".node")
+            .data(nodes)
+            .enter().append("g")
+            .attr("class", "node")
+            .attr("transform", function (d) {
+                return "rotate(" + (d.x - 90) + ")translate(" + d.y + ")";
+            })
+        node.append("circle")
+            .attr("r", 4.5);
+        node.append("text")
+            .attr("dy", ".31em")
+            .attr("text-anchor", function (d) {
+                return d.x < 180 ? "start" : "end";
+            })
+            .attr("transform", function (d) {
+                return d.x < 180 ? "translate(8)" : "rotate(180)translate(-8)";
+            })
+            .text(function (d) {
+                return d.name;
+            });
+    });
+    d3.select(self.frameElement).style("height", diameter - 150 + "px");
+</script>

algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/interpolationsearch/InterpolationSearchUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.algorithms.interpolationsearch;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class InterpolationSearchUnitTest {
+    
+    private int[] myData;
+
+    @Before
+    public void setUp() {
+        myData = new int[]{13,21,34,55,69,73,84,101};
+    }
+    
+    @Test
+    public void givenSortedArray_whenLookingFor84_thenReturn6() {
+        int pos = InterpolationSearch.interpolationSearch(myData, 84);
+        assertEquals(6, pos);
+    }
+    
+    @Test
+    public void givenSortedArray_whenLookingFor19_thenReturnMinusOne() {
+        int pos = InterpolationSearch.interpolationSearch(myData, 19);
+        assertEquals(-1, pos);
+    }
+
+}

algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/printtriangles/PrintTriangleExamplesUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.algorithms.printtriangles;
+
+import junitparams.JUnitParamsRunner;
+import junitparams.Parameters;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(JUnitParamsRunner.class)
+public class PrintTriangleExamplesUnitTest {
+    
+    private static Object[][] rightAngledTriangles() {
+        String expected0 = ""; 
+        
+        String expected2 = "*" + System.lineSeparator() 
+                         + "**" + System.lineSeparator();
+        
+        String expected5 = "*" + System.lineSeparator() 
+                         + "**" + System.lineSeparator()
+                         + "***" + System.lineSeparator()
+                         + "****" + System.lineSeparator()
+                         + "*****" + System.lineSeparator();
+        
+        String expected7 = "*" + System.lineSeparator() 
+                         + "**" + System.lineSeparator()
+                         + "***" + System.lineSeparator()
+                         + "****" + System.lineSeparator()
+                         + "*****" + System.lineSeparator()
+                         + "******" + System.lineSeparator()
+                         + "*******" + System.lineSeparator();
+        
+        return new Object[][] {
+            { 0, expected0 },
+            { 2, expected2 },
+            { 5, expected5 },
+            { 7, expected7 }
+        };
+    }
+
+    @Test
+    @Parameters(method = "rightAngledTriangles")
+    public void whenPrintARightAngledTriangleIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printARightAngledTriangle(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+    
+    private static Object[][] isoscelesTriangles() {
+        String expected0 = ""; 
+        
+        String expected2 = " *" + System.lineSeparator() 
+                         + "***" + System.lineSeparator();
+        
+        String expected5 = "    *" + System.lineSeparator() 
+                         + "   ***" + System.lineSeparator()
+                         + "  *****" + System.lineSeparator()
+                         + " *******" + System.lineSeparator()
+                         + "*********" + System.lineSeparator();
+        
+        String expected7 = "      *" + System.lineSeparator() 
+                         + "     ***" + System.lineSeparator()
+                         + "    *****" + System.lineSeparator()
+                         + "   *******" + System.lineSeparator()
+                         + "  *********" + System.lineSeparator()
+                         + " ***********" + System.lineSeparator()
+                         + "*************" + System.lineSeparator();
+        
+        return new Object[][] {
+            { 0, expected0 },
+            { 2, expected2 },
+            { 5, expected5 },
+            { 7, expected7 }
+        };
+    }
+
+    @Test
+    @Parameters(method = "isoscelesTriangles")
+    public void whenPrintAnIsoscelesTriangleIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printAnIsoscelesTriangle(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+    
+    @Test
+    @Parameters(method = "isoscelesTriangles")
+    public void whenPrintAnIsoscelesTriangleUsingSubstringIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printAnIsoscelesTriangleUsingSubstring(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+
+}

algorithms-sorting/README.md

@@ -5,3 +5,4 @@
 - [Quicksort Algorithm Implementation in Java](https://www.baeldung.com/java-quicksort)
 - [Insertion Sort in Java](https://www.baeldung.com/java-insertion-sort)
 - [Heap Sort in Java](https://www.baeldung.com/java-heap-sort)
+- [Shell Sort in Java](https://www.baeldung.com/java-shell-sort)

algorithms-sorting/src/main/java/com/baeldung/algorithms/inoutsort/InOutSort.java

@@ -0,0 +1,25 @@
+package com.baeldung.algorithms.inoutsort;
+
+public class InOutSort {
+
+    public static int[] reverseInPlace(int A[]) {
+        int n = A.length;
+        for (int i = 0; i < n / 2; i++) {
+            int temp = A[i];
+            A[i] = A[n - 1 - i];
+            A[n - 1 - i] = temp;
+        }
+
+        return A;
+    }
+
+    public static int[] reverseOutOfPlace(int A[]) {
+        int n = A.length;
+        int[] B = new int[n];
+        for (int i = 0; i < n; i++) {
+            B[n - i - 1] = A[i];
+        }
+
+        return B;
+    }
+}

algorithms-sorting/src/main/java/com/baeldung/algorithms/selectionsort/SelectionSort.java

@@ -0,0 +1,38 @@
+package com.baeldung.algorithms.selectionsort;
+
+public class SelectionSort {
+
+    public static void sortAscending(final int[] arr) {
+        for (int i = 0; i < arr.length - 1; i++) {
+            int minElementIndex = i;
+            for (int j = i + 1; j < arr.length; j++) {
+                if (arr[minElementIndex] > arr[j]) {
+                    minElementIndex = j;
+                }
+            }
+
+            if (minElementIndex != i) {
+                int temp = arr[i];
+                arr[i] = arr[minElementIndex];
+                arr[minElementIndex] = temp;
+            }
+        }
+    }
+
+    public static void sortDescending(final int[] arr) {
+        for (int i = 0; i < arr.length - 1; i++) {
+            int maxElementIndex = i;
+            for (int j = i + 1; j < arr.length; j++) {
+                if (arr[maxElementIndex] < arr[j]) {
+                    maxElementIndex = j;
+                }
+            }
+
+            if (maxElementIndex != i) {
+                int temp = arr[i];
+                arr[i] = arr[maxElementIndex];
+                arr[maxElementIndex] = temp;
+            }
+        }
+    }
+}

algorithms-sorting/src/test/java/com/baeldung/algorithms/inoutsort/InOutSortUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.algorithms.inoutsort;
+
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class InOutSortUnitTest {
+
+    @Test
+    public void givenArray_whenInPlaceSort_thenReversed() {
+        int[] input = {1, 2, 3, 4, 5, 6, 7};
+        int[] expected = {7, 6, 5, 4, 3, 2, 1};
+        assertArrayEquals("the two arrays are not equal", expected, InOutSort.reverseInPlace(input));
+    }
+
+    @Test
+    public void givenArray_whenOutOfPlaceSort_thenReversed() {
+        int[] input = {1, 2, 3, 4, 5, 6, 7};
+        int[] expected = {7, 6, 5, 4, 3, 2, 1};
+        assertArrayEquals("the two arrays are not equal", expected, InOutSort.reverseOutOfPlace(input));
+    }
+}

algorithms-sorting/src/test/java/com/baeldung/algorithms/selectionsort/SelectionSortUnitTest.java

@@ -0,0 +1,25 @@
+package com.baeldung.algorithms.selectionsort;
+
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class SelectionSortUnitTest {
+
+    @Test
+    public void givenUnsortedArray_whenSelectionSort_SortAscending_thenSortedAsc() {
+        int[] input = { 5, 4, 1, 6, 2 };
+        SelectionSort.sortAscending(input);
+        int[] expected = {1, 2, 4, 5, 6};
+        assertArrayEquals("the two arrays are not equal", expected, input);
+    }
+    
+    @Test
+    public void givenUnsortedArray_whenSelectionSort_SortDescending_thenSortedDesc() {
+        int[] input = { 5, 4, 1, 6, 2 };
+        SelectionSort.sortDescending(input);
+        int[] expected = {6, 5, 4, 2, 1};
+        assertArrayEquals("the two arrays are not equal", expected, input);
+    }
+}

core-groovy-2/README.md

@@ -8,3 +8,4 @@
 - [Pattern Matching in Strings in Groovy](https://www.baeldung.com/groovy-pattern-matching)
 - [Working with XML in Groovy](https://www.baeldung.com/groovy-xml)
 - [Integrating Groovy into Java Applications](https://www.baeldung.com/groovy-java-applications)
+- [Concatenate Strings with Groovy](https://www.baeldung.com/groovy-concatenate-strings)

core-groovy-2/src/main/groovy/com/baeldung/metaprogramming/Employee.groovy

@@ -0,0 +1,45 @@
+package com.baeldung.metaprogramming
+
+import groovy.transform.AutoClone
+import groovy.transform.Canonical
+import groovy.transform.EqualsAndHashCode
+import groovy.transform.ToString
+import groovy.transform.TupleConstructor
+import groovy.util.logging.*
+
+@Canonical
+@TupleConstructor
+@EqualsAndHashCode
+@ToString(includePackage=false, excludes=['id'])
+@Log 
+@AutoClone
+class Employee {
+
+    long id
+    String firstName
+    String lastName
+    int age
+
+    //method to catch missing property's getter
+    def propertyMissing(String propertyName) {
+        log.info "$propertyName is not available"
+        "property '$propertyName' is not available"
+    }
+
+    //method to catch missing property's setter
+    def propertyMissing(String propertyName, propertyValue) {
+        println "property '$propertyName' is not available"
+        log.info "$propertyName is not available"
+        "property '$propertyName' is not available"
+    }
+
+    def methodMissing(String methodName, def methodArgs) {
+        log.info "$methodName is not defined"
+        "method '$methodName' is not defined"
+    }
+    
+    def logEmp() {
+        log.info "Employee: $lastName, $firstName is of $age years age"
+    }
+
+}

core-groovy-2/src/main/groovy/com/baeldung/metaprogramming/extension/BasicExtensions.groovy

@@ -0,0 +1,30 @@
+package com.baeldung.metaprogramming.extension
+
+import com.baeldung.metaprogramming.Employee
+
+class BasicExtensions {
+    
+    static int getYearOfBirth(Employee self) {
+        return (new Date().getYear() + 1900) - self.age;
+    }
+    
+    static String capitalize(String self) {
+        return self.substring(0, 1).toUpperCase() + self.substring(1)
+    }
+
+    static void printCounter(Integer self) {
+        while (self>0) {
+            println self
+            self--
+        }
+    }
+    
+    static Long square(Long self) {
+        return self*self
+    }
+    
+    static BigDecimal cube(BigDecimal self) {
+        return self*self*self
+    }
+    
+}

core-groovy-2/src/main/groovy/com/baeldung/metaprogramming/extension/StaticEmployeeExtension.groovy

@@ -0,0 +1,10 @@
+package com.baeldung.metaprogramming.extension
+
+import com.baeldung.metaprogramming.Employee
+
+class StaticEmployeeExtension {
+    
+    static Employee getDefaultObj(Employee self) {
+        return new Employee(firstName: "firstName", lastName: "lastName", age: 20)
+    }
+}

core-groovy-2/src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule

@@ -0,0 +1,4 @@
+moduleName=core-groovy-2
+moduleVersion=1.0-SNAPSHOT
+extensionClasses=com.baeldung.metaprogramming.extension.BasicExtensions
+staticExtensionClasses=com.baeldung.metaprogramming.extension.StaticEmployeeExtension

core-groovy-2/src/test/groovy/com/baeldung/metaprogramming/MetaprogrammingUnitTest.groovy

@@ -0,0 +1,118 @@
+package com.baeldung.metaprogramming
+
+import groovy.time.TimeCategory
+
+class MetaprogrammingUnitTest extends GroovyTestCase {
+
+    Employee emp = new Employee(firstName: "Norman", lastName: "Lewis")
+
+    void testPropertyMissing() {
+        assert emp.address == "property 'address' is not available"
+    }
+
+    void testMethodMissing() {
+        Employee emp = new Employee()
+        try {
+            emp.getFullName()
+        } catch(MissingMethodException e) {
+            println "method is not defined"
+        }
+        assert emp.getFullName() == "method 'getFullName' is not defined"
+    }
+
+    void testMetaClassProperty() {
+        Employee.metaClass.address = ""
+        emp = new Employee(firstName: "Norman", lastName: "Lewis", address: "US")
+        assert emp.address == "US"
+    }
+
+    void testMetaClassMethod() {
+        emp.metaClass.getFullName = {
+            "$lastName, $firstName"
+        }
+        assert emp.getFullName() == "Lewis, Norman"
+    }
+
+    void testMetaClassConstructor() {
+        try {
+            Employee emp = new Employee("Norman")
+        } catch(GroovyRuntimeException e) {
+            assert e.message == "Could not find matching constructor for: com.baeldung.metaprogramming.Employee(String)"
+        }
+
+        Employee.metaClass.constructor = { String firstName ->
+            new Employee(firstName: firstName)
+        }
+
+        Employee norman = new Employee("Norman")
+        assert norman.firstName == "Norman"
+        assert norman.lastName == null
+    }
+
+    void testJavaMetaClass() {
+        String.metaClass.capitalize = { String str ->
+            str.substring(0, 1).toUpperCase() + str.substring(1);
+        }
+        assert "norman".capitalize() == "Norman"
+    }
+
+    void testEmployeeExtension() {
+        Employee emp = new Employee(age: 28)
+        assert emp.getYearOfBirth() == 1991
+    }
+
+    void testJavaClassesExtensions() {
+        5.printCounter()
+
+        assert 40l.square() == 1600l
+
+        assert (2.98).cube() == 26.463592
+    }
+
+    void testStaticEmployeeExtension() {
+        assert Employee.getDefaultObj().firstName == "firstName"
+        assert Employee.getDefaultObj().lastName == "lastName"
+        assert Employee.getDefaultObj().age == 20
+    }
+
+    void testToStringAnnotation() {
+        Employee employee = new Employee()
+        employee.id = 1
+        employee.firstName = "norman"
+        employee.lastName = "lewis"
+        employee.age = 28
+
+        assert employee.toString() == "Employee(norman, lewis, 28)"
+    }
+
+    void testTupleConstructorAnnotation() {
+        Employee norman = new Employee(1, "norman", "lewis", 28)
+        assert norman.toString() == "Employee(norman, lewis, 28)"
+
+        Employee snape = new Employee(2, "snape")
+        assert snape.toString() == "Employee(snape, null, 0)"
+
+    }
+    
+    void testEqualsAndHashCodeAnnotation() {
+        Employee norman = new Employee(1, "norman", "lewis", 28)
+        Employee normanCopy = new Employee(1, "norman", "lewis", 28)
+        assert norman.equals(normanCopy)
+        assert norman.hashCode() == normanCopy.hashCode()
+    }
+    
+    void testAutoCloneAnnotation() {
+        try {
+            Employee norman = new Employee(1, "norman", "lewis", 28)
+            def normanCopy = norman.clone()
+            assert norman == normanCopy
+        } catch(CloneNotSupportedException e) {
+            e.printStackTrace()
+        }
+    }
+
+    void testLoggingAnnotation() {
+        Employee employee = new Employee(1, "Norman", "Lewis", 28)
+        employee.logEmp()
+    }
+}

core-java-modules/core-java-8-2/README.md

@@ -7,3 +7,4 @@
 - [How to Delay Code Execution in Java](https://www.baeldung.com/java-delay-code-execution)
 - [Run JAR Application With Command Line Arguments](https://www.baeldung.com/java-run-jar-with-arguments)
 - [Java 8 Stream skip() vs limit()](https://www.baeldung.com/java-stream-skip-vs-limit)
+- [Guide to Java BiFunction Interface](https://www.baeldung.com/java-bifunction-interface)

core-java-modules/core-java-8/README.md

@@ -4,14 +4,10 @@
 
 ### Relevant Articles: 
 - [Guide to Java 8’s Collectors](http://www.baeldung.com/java-8-collectors)
-- [Functional Interfaces in Java 8](http://www.baeldung.com/java-8-functional-interfaces)
-- [Java 8 – Powerful Comparison with Lambdas](http://www.baeldung.com/java-8-sort-lambda)
 - [New Features in Java 8](http://www.baeldung.com/java-8-new-features)
-- [Lambda Expressions and Functional Interfaces: Tips and Best Practices](http://www.baeldung.com/java-8-lambda-expressions-tips)
 - [The Double Colon Operator in Java 8](http://www.baeldung.com/java-8-double-colon-operator)
 - [Guide to Java 8 groupingBy Collector](http://www.baeldung.com/java-groupingby-collector)
 - [Strategy Design Pattern in Java 8](http://www.baeldung.com/java-strategy-pattern)
-- [Exceptions in Java 8 Lambda Expressions](http://www.baeldung.com/java-lambda-exceptions)
 - [Guide to Java 8 Comparator.comparing()](http://www.baeldung.com/java-8-comparator-comparing)
 - [Guide To Java 8 Optional](http://www.baeldung.com/java-optional)
 - [Guide to the Java 8 forEach](http://www.baeldung.com/foreach-java)
@@ -38,6 +34,5 @@
 - [Java @SafeVarargs Annotation](https://www.baeldung.com/java-safevarargs)
 - [Java @Deprecated Annotation](https://www.baeldung.com/java-deprecated)
 - [Java 8 Predicate Chain](https://www.baeldung.com/java-predicate-chain)
-- [Method References in Java](https://www.baeldung.com/java-method-references)
 - [Creating a Custom Annotation in Java](https://www.baeldung.com/java-custom-annotation)
 - [The Difference Between Collection.stream().forEach() and Collection.forEach()](https://www.baeldung.com/java-collection-stream-foreach)

core-java-modules/core-java-arrays-2/README.MD

@@ -1,3 +1,5 @@
 ## Relevant Articles
 
 - [Extending an Array’s Length](https://www.baeldung.com/java-array-add-element-at-the-end)
+- [Checking If an Array Is Sorted in Java](https://www.baeldung.com/java-check-sorted-array)
+- [Looping Diagonally Through a 2d Java Array](https://www.baeldung.com/java-loop-diagonal-array)

core-java-modules/core-java-arrays/README.md

@@ -7,7 +7,7 @@
 - [Check if a Java Array Contains a Value](http://www.baeldung.com/java-array-contains-value)
 - [Initializing Arrays in Java](http://www.baeldung.com/java-initialize-array)
 - [Guide to the java.util.Arrays Class](http://www.baeldung.com/java-util-arrays)
-- [Jagged Arrays In Java](http://www.baeldung.com/java-jagged-arrays)
+- [Multi-Dimensional Arrays In Java](http://www.baeldung.com/java-jagged-arrays)
 - [Find Sum and Average in a Java Array](http://www.baeldung.com/java-array-sum-average)
 - [Arrays in Java: A Reference Guide](https://www.baeldung.com/java-arrays-guide)
 - [How to Invert an Array in Java](http://www.baeldung.com/java-invert-array)
@@ -16,3 +16,4 @@
 - [Sorting Arrays in Java](https://www.baeldung.com/java-sorting-arrays)
 - [Convert a Float to a Byte Array in Java](https://www.baeldung.com/java-convert-float-to-byte-array)
 - [Converting Between Stream and Array in Java](https://www.baeldung.com/java-stream-to-array)
+- [Removing an Element from an Array in Java](https://www.baeldung.com/java-array-remove-element)

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/mutex/SequenceGenerator.java

@@ -0,0 +1,11 @@
+package com.baeldung.concurrent.mutex;
+
+public class SequenceGenerator {
+    private int currentValue = 0;
+
+    public int getNextSequence() throws InterruptedException {
+        currentValue = currentValue + 1;
+        Thread.sleep(500);
+        return currentValue;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingMonitor.java

@@ -0,0 +1,18 @@
+package com.baeldung.concurrent.mutex;
+
+import com.google.common.util.concurrent.Monitor;
+
+public class SequenceGeneratorUsingMonitor extends SequenceGenerator {
+
+    private Monitor monitor = new Monitor();
+
+    @Override
+    public int getNextSequence() throws InterruptedException {
+        monitor.enter();
+        try {
+            return super.getNextSequence();
+        } finally {
+            monitor.leave();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingReentrantLock.java

@@ -0,0 +1,18 @@
+package com.baeldung.concurrent.mutex;
+
+import java.util.concurrent.locks.ReentrantLock;
+
+public class SequenceGeneratorUsingReentrantLock extends SequenceGenerator {
+
+    private ReentrantLock mutex = new ReentrantLock();
+
+    @Override
+    public int getNextSequence() throws InterruptedException {
+        try {
+            mutex.lock();
+            return super.getNextSequence();
+        } finally {
+            mutex.unlock();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingSemaphore.java

@@ -0,0 +1,18 @@
+package com.baeldung.concurrent.mutex;
+
+import java.util.concurrent.Semaphore;
+
+public class SequenceGeneratorUsingSemaphore extends SequenceGenerator {
+
+    private Semaphore mutex = new Semaphore(1);
+
+    @Override
+    public int getNextSequence() throws InterruptedException {
+        try {
+            mutex.acquire();
+            return super.getNextSequence();
+        } finally {
+            mutex.release();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingSynchronizedBlock.java

@@ -0,0 +1,12 @@
+package com.baeldung.concurrent.mutex;
+
+public class SequenceGeneratorUsingSynchronizedBlock extends SequenceGenerator {
+
+    @Override
+    public int getNextSequence() throws InterruptedException {
+        synchronized (this) {
+            return super.getNextSequence();
+        }
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/mutex/SequenceGeneratorUsingSynchronizedMethod.java

@@ -0,0 +1,10 @@
+package com.baeldung.concurrent.mutex;
+
+public class SequenceGeneratorUsingSynchronizedMethod extends SequenceGenerator {
+
+    @Override
+    public synchronized int getNextSequence() throws InterruptedException {
+        return super.getNextSequence();
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/test/java/com/baeldung/concurrent/mutex/MutexUnitTest.java

@@ -0,0 +1,81 @@
+package com.baeldung.concurrent.mutex;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.baeldung.concurrent.mutex.SequenceGenerator;
+import com.baeldung.concurrent.mutex.SequenceGeneratorUsingMonitor;
+import com.baeldung.concurrent.mutex.SequenceGeneratorUsingReentrantLock;
+import com.baeldung.concurrent.mutex.SequenceGeneratorUsingSemaphore;
+import com.baeldung.concurrent.mutex.SequenceGeneratorUsingSynchronizedBlock;
+import com.baeldung.concurrent.mutex.SequenceGeneratorUsingSynchronizedMethod;
+
+public class MutexUnitTest {
+
+    private final int RANGE = 30;
+
+    @Test
+    public void givenUnsafeSequenceGenerator_whenRaceCondition_thenUnexpectedBehavior() throws Exception {
+        Set<Integer> uniqueSequences = getASetOFUniqueSequences(new SequenceGenerator());
+        Assert.assertNotEquals(RANGE, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingSynchronizedMethod_whenRaceCondition_thenSuccess() throws Exception {
+        Set<Integer> uniqueSequences = getASetOFUniqueSequences(new SequenceGeneratorUsingSynchronizedMethod());
+        Assert.assertEquals(RANGE, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingSynchronizedBlock_whenRaceCondition_thenSuccess() throws Exception {
+        Set<Integer> uniqueSequences = getASetOFUniqueSequences(new SequenceGeneratorUsingSynchronizedBlock());
+        Assert.assertEquals(RANGE, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingReentrantLock_whenRaceCondition_thenSuccess() throws Exception {
+        Set<Integer> uniqueSequences = getASetOFUniqueSequences(new SequenceGeneratorUsingReentrantLock());
+        Assert.assertEquals(RANGE, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingSemaphore_whenRaceCondition_thenSuccess() throws Exception {
+        Set<Integer> uniqueSequences = getASetOFUniqueSequences(new SequenceGeneratorUsingSemaphore());
+        Assert.assertEquals(RANGE, uniqueSequences.size());
+    }
+
+    @Test
+    public void givenSequenceGeneratorUsingMonitor_whenRaceCondition_thenSuccess() throws Exception {
+        Set<Integer> uniqueSequences = getASetOFUniqueSequences(new SequenceGeneratorUsingMonitor());
+        Assert.assertEquals(RANGE, uniqueSequences.size());
+    }
+
+    private Set<Integer> getASetOFUniqueSequences(SequenceGenerator generator) throws Exception {
+        ExecutorService executor = Executors.newFixedThreadPool(3);
+        Set<Integer> uniqueSequences = new HashSet<>();
+        List<Future<Integer>> futures = new ArrayList<>();
+
+        for (int i = 0; i < RANGE; i++) {
+            futures.add(executor.submit(generator::getNextSequence));
+        }
+
+        for (Future<Integer> future : futures) {
+            uniqueSequences.add(future.get());
+        }
+
+        executor.awaitTermination(15, TimeUnit.SECONDS);
+        executor.shutdown();
+
+        return uniqueSequences;
+    }
+
+}

core-java-modules/core-java-jndi/pom.xml

@@ -0,0 +1,65 @@
+<?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>
+
+    <groupId>com.baeldung.jndi</groupId>
+    <artifactId>core-java-jndi</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>../../</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.5.1</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-core</artifactId>
+            <version>5.0.9.RELEASE</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-context</artifactId>
+            <version>5.0.9.RELEASE</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-jdbc</artifactId>
+            <version>5.0.9.RELEASE</version>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-test</artifactId>
+            <version>5.0.9.RELEASE</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <version>1.4.199</version>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+</project>

core-java-modules/core-java-jndi/src/test/java/com/baeldung/jndi/JndiUnitTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.jndi;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.springframework.jdbc.datasource.DriverManagerDataSource;
+import org.springframework.jndi.JndiTemplate;
+import org.springframework.mock.jndi.SimpleNamingContextBuilder;
+
+import javax.naming.*;
+import javax.sql.DataSource;
+
+import java.util.Enumeration;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class JndiUnitTest {
+
+    private static InitialContext ctx;
+    private static DriverManagerDataSource ds;
+
+    @BeforeAll
+    static void setUp() throws Exception {
+        SimpleNamingContextBuilder builder = new SimpleNamingContextBuilder();
+        ds = new DriverManagerDataSource("jdbc:h2:mem:mydb");
+        builder.activate();
+
+        JndiTemplate jndiTemplate = new JndiTemplate();
+        ctx = (InitialContext) jndiTemplate.getContext();
+    }
+
+    @Test
+    void givenACompositeName_whenAddingAnElement_thenNameIncludesIt() throws Exception {
+        Name objectName = new CompositeName("java:comp/env/jdbc");
+
+        Enumeration<String> elements = objectName.getAll();
+        while(elements.hasMoreElements()) {
+            System.out.println(elements.nextElement());
+        }
+
+        objectName.add("example");
+
+        assertEquals("env", objectName.get(1));
+        assertEquals("example", objectName.get(objectName.size() - 1));
+    }
+
+    @Test
+    void givenADataSource_whenAddingDriver_thenBind() throws Exception {
+        ds.setDriverClassName("org.h2.Driver");
+        ctx.bind("java:comp/env/jdbc/datasource", ds);
+    }
+
+    @Test
+    void givenContext_whenLookupByName_thenValidDataSource() throws Exception {
+        DataSource ds = (DataSource) ctx.lookup("java:comp/env/jdbc/datasource");
+
+        assertNotNull(ds);
+        assertNotNull(ds.getConnection());
+    }
+
+}

core-java-modules/core-java-jndi/src/test/java/com/baeldung/jndi/exceptions/JndiExceptionsUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.jndi.exceptions;
+
+import org.junit.jupiter.api.MethodOrderer;
+import org.junit.jupiter.api.Order;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestMethodOrder;
+import org.springframework.jndi.JndiTemplate;
+import org.springframework.mock.jndi.SimpleNamingContextBuilder;
+
+import javax.naming.InitialContext;
+import javax.naming.NameNotFoundException;
+import javax.naming.NoInitialContextException;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
+public class JndiExceptionsUnitTest {
+
+    @Test
+    @Order(1)
+    void givenNoContext_whenLookupObject_thenThrowNoInitialContext() {
+        assertThrows(NoInitialContextException.class, () -> {
+            JndiTemplate jndiTemplate = new JndiTemplate();
+            InitialContext ctx = (InitialContext) jndiTemplate.getContext();
+            ctx.lookup("java:comp/env/jdbc/datasource");
+        }).printStackTrace();
+    }
+
+    @Test
+    @Order(2)
+    void givenEmptyContext_whenLookupNotBounds_thenThrowNameNotFound() {
+        assertThrows(NameNotFoundException.class, () -> {
+            SimpleNamingContextBuilder builder = new SimpleNamingContextBuilder();
+            builder.activate();
+
+            JndiTemplate jndiTemplate = new JndiTemplate();
+            InitialContext ctx = (InitialContext) jndiTemplate.getContext();
+            ctx.lookup("badJndiName");
+        }).printStackTrace();
+    }
+
+}

core-java-modules/core-java-jpms/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles
+
+- [Design Strategies for Decoupling Java Modules](https://www.baeldung.com/java-modules-decoupling-design-strategies)

core-java-modules/core-java-lambdas/README.md

@@ -1,3 +1,8 @@
 ## Relevant articles:
 
 - [Why Do Local Variables Used in Lambdas Have to Be Final or Effectively Final?](https://www.baeldung.com/java-lambda-effectively-final-local-variables)
+- [Java 8 – Powerful Comparison with Lambdas](http://www.baeldung.com/java-8-sort-lambda)
+- [Functional Interfaces in Java 8](http://www.baeldung.com/java-8-functional-interfaces)
+- [Lambda Expressions and Functional Interfaces: Tips and Best Practices](http://www.baeldung.com/java-8-lambda-expressions-tips)
+- [Exceptions in Java 8 Lambda Expressions](http://www.baeldung.com/java-lambda-exceptions)
+- [Method References in Java](https://www.baeldung.com/java-method-references)

core-java-modules/core-java-lambdas/pom.xml

@@ -15,5 +15,11 @@
     <relativePath>../../parent-java</relativePath>
   </parent>
 
-
+  <dependencies>
+    <dependency>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-lang3</artifactId>
+      <version>${commons-lang3.version}</version>
+    </dependency>
+  </dependencies>
 </project>

core-java-modules/core-java-lang-operators/pom.xml

@@ -0,0 +1,43 @@
+<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-lang-operators</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-lang-operators</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-lang-operators</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+        <!-- testing -->
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+
+</project>

core-java-modules/core-java-lang-operators/src/test/java/com/baeldung/unaryoperators/IncrementDecrementUnaryOperatorUnitTest.java

@@ -1,6 +1,7 @@
-package com.baeldung.incrementdecrementunaryoperator;
+package com.baeldung.unaryoperators;
 
 import static org.assertj.core.api.Assertions.assertThat;
+
 import org.junit.Test;
 
 public class IncrementDecrementUnaryOperatorUnitTest {

core-java-modules/core-java-lang-syntax/README.md

@@ -18,3 +18,4 @@
 - [The Modulo Operator in Java](https://www.baeldung.com/modulo-java)
 - [Ternary Operator In Java](https://www.baeldung.com/java-ternary-operator)
 - [Java instanceof Operator](https://www.baeldung.com/java-instanceof)
+- [Breaking Out of Nested Loops](https://www.baeldung.com/java-breaking-out-nested-loop)

core-java-modules/core-java-networking-2/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles
+
+- [Checking if a URL Exists in Java](https://www.baeldung.com/java-check-url-exists)

core-java-modules/core-java-nio/README.md

@@ -1,3 +1,3 @@
-## Relevant articles:
+## Relevant Articles:
 
-- [Determine File Creating Date in Java](https://www.baeldung.com/java-file-creation-date)
+- [Determine File Creation Date in Java](https://www.baeldung.com/java-file-creation-date)

core-java-modules/core-java-nio/src/main/java/com/baeldung/file/Main.java

@@ -1,12 +1,13 @@
-package com.baeldung.files;
+package com.baeldung.file;
 
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingApacheCommonsIO;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingBufferedReader;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingGoogleGuava;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingLineNumberReader;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFileChannel;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFiles;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingScanner;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingApacheCommonsIO;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingBufferedReader;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingGoogleGuava;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingLineNumberReader;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFileChannel;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFiles;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFilesReadAllLines;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingScanner;
 
 public class Main {
 
@@ -17,6 +18,7 @@ public class Main {
         System.out.printf("Total Number of Lines Using LineNumberReader: %s%n", getTotalNumberOfLinesUsingLineNumberReader(INPUT_FILE_NAME));
         System.out.printf("Total Number of Lines Using Scanner: %s%n", getTotalNumberOfLinesUsingScanner(INPUT_FILE_NAME));
         System.out.printf("Total Number of Lines Using NIO Files: %s%n", getTotalNumberOfLinesUsingNIOFiles(INPUT_FILE_NAME));
+        System.out.printf("Total Number of Lines Using NIO Files#readAllLines: %s%n", getTotalNumberOfLinesUsingNIOFilesReadAllLines(INPUT_FILE_NAME));
         System.out.printf("Total Number of Lines Using NIO FileChannel: %s%n", getTotalNumberOfLinesUsingNIOFileChannel(INPUT_FILE_NAME));
         System.out.printf("Total Number of Lines Using Apache Commons IO: %s%n", getTotalNumberOfLinesUsingApacheCommonsIO(INPUT_FILE_NAME));
         System.out.printf("Total Number of Lines Using NIO Google Guava: %s%n", getTotalNumberOfLinesUsingGoogleGuava(INPUT_FILE_NAME));

core-java-modules/core-java-nio/src/main/java/com/baeldung/file/NumberOfLineFinder.java

@@ -1,4 +1,4 @@
-package com.baeldung.files;
+package com.baeldung.file;
 
 import java.io.BufferedReader;
 import java.io.File;
@@ -67,6 +67,17 @@ public class NumberOfLineFinder {
         return lines;
     }
 
+    public static int getTotalNumberOfLinesUsingNIOFilesReadAllLines(String fileName) {
+        int lines = 0;
+        try {
+            List<String> fileStream = Files.readAllLines(Paths.get(fileName));
+            lines = fileStream.size();
+        } catch (IOException ioe) {
+            ioe.printStackTrace();
+        }
+        return lines;
+    }
+
     public static int getTotalNumberOfLinesUsingNIOFileChannel(String fileName) {
         int lines = 1;
         try (FileChannel channel = FileChannel.open(Paths.get(fileName), StandardOpenOption.READ)) {

core-java-modules/core-java-nio/src/main/resources/input.txt

@@ -0,0 +1,45 @@
+Lorem ipsum dolor sit amet, consectetur adipiscing elit. In lacus enim, scelerisque id sapien ut, semper euismod quam. Nunc ullamcorper semper blandit. Praesent quis quam mollis, iaculis lectus a, fringilla leo. Interdum et malesuada fames ac ante ipsum primis in faucibus. Duis vitae auctor mauris. Pellentesque eu pellentesque lorem, vel ultricies libero. Pellentesque vestibulum sagittis eros. In vestibulum lacus elit. Interdum et malesuada fames ac ante ipsum primis in faucibus.
+
+Vivamus pharetra lacus fringilla nisl molestie eleifend. Donec et dolor non quam mattis mattis. Proin malesuada maximus elit id semper. Donec facilisis dolor ut feugiat auctor. Proin accumsan semper consectetur. Vivamus facilisis odio vel bibendum imperdiet. Sed rutrum nisi nec nisi interdum fringilla. Aliquam laoreet velit ullamcorper egestas ultrices. Aliquam ultricies sem sed orci interdum, eu porta purus malesuada. Sed accumsan, nunc ut maximus rhoncus, arcu ante pretium ex, non ultrices magna nisi et velit. Pellentesque tempor mi quis lacus consectetur, quis imperdiet enim efficitur. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas.
+
+Nunc sed maximus erat. Aenean imperdiet finibus massa ac aliquam. Interdum et malesuada fames ac ante ipsum primis in faucibus. Duis dignissim cursus purus, eu tempus urna. Nunc sed mauris scelerisque, luctus eros ut, viverra nisi. Maecenas congue sed ligula in eleifend. Praesent nec dignissim enim, dictum efficitur massa. Nullam eros dui, rutrum quis aliquam accumsan, sollicitudin cursus eros. Phasellus euismod, lorem vitae vehicula ullamcorper, leo lorem vestibulum magna, vitae malesuada libero ipsum id lorem. Aenean finibus turpis facilisis tortor bibendum, vitae dignissim dolor dictum. Ut quis ornare nisi, non rutrum sapien.
+
+Etiam placerat, est eget placerat imperdiet, neque urna tristique est, a dictum nisl dolor vitae leo. Vivamus porttitor mi vitae volutpat ultrices. Quisque at ante porta mauris ultricies iaculis. Phasellus iaculis sollicitudin urna nec facilisis. Suspendisse dapibus vulputate scelerisque. Fusce felis diam, eleifend in tristique in, malesuada a purus. Suspendisse euismod ipsum sed urna imperdiet, quis venenatis lacus dapibus. Maecenas vitae est vel sem fringilla ornare at ut mi. Quisque porta, nulla at rutrum fringilla, mi ligula egestas libero, ac convallis elit diam et sapien. Vestibulum purus tortor, ornare ut enim sed, mattis lobortis erat. Maecenas ac ante tincidunt, euismod mauris a, fermentum diam. Nullam arcu est, consequat sed enim in, bibendum aliquet velit. Donec bibendum magna ac augue sagittis vehicula. Curabitur nec mauris eu augue bibendum volutpat. Fusce fringilla varius fringilla.
+
+Aliquam faucibus massa non orci accumsan, porta consectetur diam vulputate. Nullam nec erat mollis, imperdiet libero nec, tincidunt neque. Aenean varius purus nec est auctor, sed vulputate libero varius. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent vel neque elit. Donec vulputate fermentum nulla, ut aliquam neque tempor in. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Donec vel venenatis est. Suspendisse luctus elit quis dui dapibus, id sodales dolor cursus. Curabitur ut vehicula dui. Fusce aliquet est et ante feugiat, et tempus ex congue. Nunc eget dapibus leo. Nunc eu accumsan diam. Suspendisse risus eros, rutrum et volutpat in, consequat in nulla. Suspendisse id felis a orci accumsan iaculis.
+
+Duis tincidunt diam eget tortor aliquet sodales. Etiam sodales purus ac urna mollis, et cursus enim porttitor. Nulla viverra ligula nunc, ornare condimentum felis posuere sed. Fusce aliquet pretium sagittis. Sed ac mi elementum massa dictum ornare. Integer quis dapibus lectus. Curabitur in rhoncus justo, et vulputate justo. Integer eget efficitur felis.
+
+Sed finibus vel tortor ac egestas. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Maecenas vestibulum nulla mi, blandit efficitur sapien fermentum eu. Integer sed turpis eros. Phasellus sed aliquam ligula. Etiam dictum quam in dapibus mattis. Donec et tristique quam. Pellentesque gravida luctus dolor, eu ornare sapien. Donec justo ante, lacinia non sem et, ultricies dignissim nibh. Vivamus eu nisl et magna pulvinar efficitur. Sed at vehicula lectus, sit amet luctus sem. Morbi vehicula sapien nisi, nec sagittis orci vestibulum et.
+
+Praesent non finibus diam. Quisque sit amet nisl vitae augue lobortis commodo. Morbi ullamcorper, tortor id ornare maximus, erat ipsum ullamcorper ipsum, in imperdiet diam sem vel erat. Sed pellentesque quis ex sed volutpat. Vestibulum volutpat diam ac dignissim sollicitudin. Praesent at luctus ex, at volutpat dui. Nunc nulla dui, lobortis et pharetra quis, efficitur in turpis. Donec sodales auctor purus id mollis. Sed auctor eu erat eget bibendum. Mauris tincidunt ornare neque id consequat. Suspendisse non massa ante. Quisque velit enim, rhoncus at erat eget, scelerisque placerat elit. Donec finibus luctus dolor. In sed eleifend lorem. Sed tempor ullamcorper lorem nec tristique. Fusce nec volutpat neque, id elementum est.
+
+Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum mattis elementum tellus, vitae maximus nulla eleifend ut. Vestibulum eu nibh vulputate, posuere felis eget, aliquet ex. Nullam leo ex, lacinia a ante ac, accumsan efficitur ligula. Vestibulum ornare gravida tempus. Proin rhoncus felis sit amet dolor commodo facilisis. Integer aliquet, diam sed pharetra feugiat, sem massa mollis orci, eget pretium libero nunc at quam. Ut rhoncus quam vitae massa hendrerit, ornare condimentum odio varius. Donec odio sapien, tristique eget libero ac, interdum facilisis odio. Phasellus nec mauris vel dolor semper mattis et quis ligula. Donec nec porttitor nunc. Integer maximus quam vitae sem gravida, ut commodo ex porttitor.
+
+Sed cursus nisi turpis, vel laoreet massa blandit ut. Cras posuere velit nulla, nec pellentesque ipsum dignissim eget. Donec pharetra, ex et commodo viverra, leo dolor dapibus tellus, vel dignissim est sem ac lectus. Quisque a arcu dapibus, aliquet magna sed, rhoncus neque. Integer suscipit, nulla ac varius lacinia, orci metus scelerisque neque, a laoreet nibh risus vitae dolor. Pellentesque felis metus, pulvinar vel cursus id, ultrices non purus. Donec mi lectus, faucibus sit amet nunc at, sagittis pretium lectus. Fusce nec purus arcu. Mauris neque neque, blandit eget mi at, auctor tempus orci. Mauris sapien lorem, luctus nec tellus non, porttitor aliquam dui.
+
+Mauris non ex risus. Aliquam imperdiet in eros eget placerat. Sed congue sed sapien porta sollicitudin. Phasellus tempor hendrerit metus vitae tincidunt. Suspendisse congue nisi sed augue dapibus, at pretium ante mollis. Cras non posuere nulla. Proin malesuada finibus magna vel iaculis. Cras in dapibus lorem. Pellentesque volutpat dolor sit amet magna tincidunt mollis. Nunc et lectus sodales, accumsan est vitae, ornare augue. Maecenas malesuada arcu leo, eget blandit lectus porttitor et. Nam aliquam sapien sit amet purus consequat lobortis. Aenean varius, augue porta dignissim efficitur, felis velit dapibus leo, tincidunt ultricies magna felis id ligula. Duis hendrerit, lectus eu elementum euismod, elit lectus consequat mi, sit amet egestas justo massa ut urna. Proin eleifend interdum ultrices.
+
+Donec lacinia orci pharetra ornare tincidunt. Nulla facilisi. Maecenas malesuada dui ac elit sagittis tincidunt id dictum dolor. Quisque lobortis purus ac metus volutpat viverra. Proin finibus sapien ut odio semper consectetur. Sed gravida luctus egestas. Mauris pretium volutpat elit, at commodo arcu sagittis nec. Ut condimentum fringilla urna ac dignissim. Cras aliquam metus pulvinar, pulvinar nibh at, placerat arcu. Nulla ornare tortor sed lectus mollis, vitae fringilla tellus egestas. Vivamus efficitur tincidunt sapien, sed finibus mi congue eu. Nullam magna velit, lacinia vitae ligula eget, molestie consectetur felis. Suspendisse varius turpis orci, ac laoreet arcu accumsan sed. Fusce quis fermentum lacus, nec varius libero. Pellentesque ac odio ut justo lobortis elementum sit amet vehicula lorem. Nulla interdum nulla eget mi tristique, vitae egestas nunc egestas.
+
+Curabitur commodo libero eu elit tincidunt, quis placerat risus vehicula. Vestibulum vehicula id nunc iaculis fermentum. Aenean semper, tellus ac semper rutrum, justo lorem feugiat leo, quis vulputate neque dui non ligula. Etiam egestas, enim eget tempor porta, nunc est tristique ante, vel suscipit massa lorem vel diam. Donec faucibus ante id turpis rhoncus congue. Nullam laoreet, diam efficitur scelerisque consequat, ligula leo ultrices est, non fermentum elit mauris ut dolor. Morbi non porttitor lorem. Sed volutpat sapien et lorem porttitor, ultricies ultricies tellus congue. Mauris sodales, tortor nec sagittis finibus, dui odio aliquet nibh, in luctus sapien massa eu risus. Nulla in est sed ante molestie vehicula vel nec lectus. Fusce maximus a quam eget aliquam. Vivamus pulvinar quis nisi a maximus. Proin cursus lacus sapien, et hendrerit elit pretium a. Donec tellus lectus, consectetur id dolor a, luctus rutrum libero. Suspendisse auctor scelerisque dui, nec pellentesque felis viverra nec. Cras elit ex, varius sed pulvinar sed, suscipit ultrices lacus.
+
+Vivamus eu luctus lectus. Maecenas congue magna orci, quis semper nulla blandit vel. Phasellus dignissim risus placerat lacinia sagittis. Praesent at gravida nisi, at pulvinar diam. Nulla egestas lectus sed felis facilisis egestas. Curabitur posuere gravida urna eu vestibulum. Pellentesque at dolor gravida, placerat quam sit amet, fermentum ligula. Morbi fringilla, mi eget mollis dictum, neque dolor ullamcorper leo, a rutrum libero ipsum eget orci. Curabitur consectetur iaculis vestibulum. Suspendisse ultricies ligula et neque lacinia luctus. Sed dignissim neque id eros sollicitudin pellentesque.
+
+Donec et magna quis lectus pharetra finibus a fringilla sapien. Phasellus accumsan, erat eu sodales cursus, tortor elit dapibus risus, ut ornare neque arcu in tellus. Nam ac vehicula diam, at aliquam nisl. Cras in sem eget nisi ultrices rutrum sit amet eu velit. Sed molestie tellus eget ante scelerisque, sit amet pulvinar neque fringilla. Nunc volutpat facilisis egestas. Cras sodales dui ac massa egestas, in mattis leo rhoncus. Pellentesque vitae urna vehicula ipsum sodales suscipit. Sed commodo tempus fringilla.
+
+Etiam egestas elit vitae mi maximus fringilla quis eget libero. Fusce finibus ultrices tellus at molestie. Pellentesque posuere blandit elementum. Etiam eu erat eu urna hendrerit euismod. Nulla quis lectus rhoncus, ultricies urna eget, pretium neque. Cras sit amet ipsum sit amet purus rutrum ultricies nec vitae tortor. Sed tempor dapibus augue in pulvinar. Ut pretium sapien in malesuada accumsan. Donec eget ultrices erat, ut efficitur ligula. Sed posuere mauris est, nec convallis ipsum tempus non.
+
+Duis a ullamcorper ante. Quisque eu ultricies metus, at aliquet odio. Nullam tempus molestie augue ut varius. Fusce purus eros, dictum nec finibus sed, sodales et diam. Suspendisse sed mi purus. Donec eleifend ipsum diam, nec fringilla enim laoreet non. Phasellus condimentum, magna sit amet porttitor suscipit, arcu risus lobortis dolor, ac fringilla nibh nisl vel purus. Phasellus facilisis posuere orci sit amet tempus. Nam nec enim maximus, rhoncus felis a, rutrum diam.
+
+Suspendisse potenti. Donec vel tempor neque. In aliquet nulla in eleifend bibendum. Sed sapien sem, finibus in sodales vitae, euismod in sem. Phasellus nec elit a erat pulvinar semper. Aliquam luctus nisl in libero molestie aliquam. Nunc ac ornare felis. Ut non mauris ut ipsum rhoncus pretium. Curabitur tristique lacus a sagittis aliquam. Morbi vel volutpat tellus. Maecenas volutpat, lacus sed tempus imperdiet, eros tellus volutpat nisi, a egestas augue nulla quis arcu. In sollicitudin imperdiet efficitur. Suspendisse viverra aliquet nisi, congue ultrices arcu hendrerit in.
+
+Maecenas vitae vestibulum nunc. Nullam semper faucibus tincidunt. Etiam sed hendrerit risus. Proin gravida, urna nec tincidunt tempus, nulla sapien porttitor nibh, porttitor lobortis nunc quam et tortor. Praesent ut varius lacus, ut hendrerit enim. Ut nec turpis ac felis imperdiet bibendum. Phasellus porttitor enim odio, et vehicula mi convallis vel. Quisque porta scelerisque sagittis. Praesent dignissim sagittis vulputate. Aenean non justo ac est volutpat bibendum. Aliquam mattis, sapien dapibus pellentesque semper, velit urna malesuada diam, nec varius nibh eros at erat. Proin leo ante, ultricies id velit ut, faucibus porta nibh. Sed nec fermentum urna, sed mollis leo. Aliquam erat volutpat.
+
+Donec condimentum, urna sed hendrerit vestibulum, ante nibh lacinia dui, in tincidunt odio sem eget orci. In hac habitasse platea dictumst. Mauris id ex id ante tempus finibus eu sagittis erat. Quisque interdum urna risus, vel varius nibh euismod non. Nulla eget pellentesque quam. Aliquam vestibulum ac tortor non lobortis. Sed vitae erat sed libero dignissim dictum nec in turpis. Vivamus id ornare elit, ut facilisis lectus. Morbi dictum purus eget ipsum dignissim porttitor. Sed at vehicula purus, nec rhoncus quam. Nunc a nisl quis arcu blandit fermentum vel quis odio. Vivamus rhoncus, sapien sed lacinia hendrerit, velit urna fermentum dolor, id feugiat magna ligula sed urna. Proin euismod efficitur libero, eget porttitor lacus tempus quis. Duis tincidunt quis est a laoreet. Nam sit amet tristique nisl, sit amet mattis mi.
+
+Aenean id dictum nulla, sed laoreet magna. Morbi consectetur in turpis at aliquam. Maecenas rutrum feugiat metus, at ullamcorper augue fermentum ut. Vivamus in magna pretium nibh dictum rhoncus luctus at orci. In hac habitasse platea dictumst. Fusce convallis, nulla nec hendrerit suscipit, ipsum diam lobortis sem, vitae elementum lectus erat sit amet magna. Quisque sollicitudin fringilla purus, ac molestie justo congue vitae. Nulla sapien leo, ullamcorper ac tellus in, cursus rhoncus enim. Suspendisse rutrum magna non ex elementum elementum id vitae enim. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Suspendisse ornare libero eu molestie pulvinar. Phasellus faucibus, magna eget rutrum porta, lorem turpis blandit lectus, eu viverra massa risus et ex.
+
+Ut consectetur eros lacus, ac ullamcorper lacus mattis a. Cras congue justo ut erat interdum, et scelerisque nisi malesuada. Quisque sed sapien sollicitudin purus tincidunt finibus vestibulum vel dolor. Cras iaculis bibendum erat, a dictum urna viverra et. Integer non neque vulputate, tincidunt purus nec, rutrum arcu. Aliquam nec magna non sem semper laoreet quis at quam. Mauris dui lectus, convallis eu efficitur at, facilisis nec lorem. Cras felis sem, egestas ac rutrum vel, mollis et ex. Aenean semper egestas libero, nec commodo mi blandit efficitur. Duis nec quam in massa dignissim sagittis vel vitae leo. Nam molestie hendrerit auctor.
+
+Sed suscipit egestas tellus sed cursus. Donec vel massa sit amet dui condimentum accumsan. Phasellus libero eros, lobortis a nisi id, porttitor maximus lectus. Praesent consectetur diam urna, id viverra turpis elementum in. Vivamus vitae pretium justo, nec tempor felis. Vivamus volutpat ultricies magna. Suspendisse vulputate lectus ac orci volutpat ullamcorper. Nulla eu leo pretium, commodo arcu accumsan, tempor nisl. Fusce sit amet tellus a ipsum vehicula laoreet sed vitae mauris. Duis porttitor massa mattis nibh placerat consequat. Fusce rutrum commodo tortor eget pellentesque. Suspendisse tempor enim libero, consequat dictum nibh dictum varius. Pellentesque feugiat sit amet urna sed facilisis. Curabitur a sagittis augue.

core-java-modules/core-java-nio/src/test/java/com/baeldung/file/NumberOfLineFinderUnitTest.java

@@ -1,12 +1,13 @@
 package com.baeldung.file;
 
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingApacheCommonsIO;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingBufferedReader;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingGoogleGuava;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingLineNumberReader;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFileChannel;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFiles;
-import static com.baeldung.files.NumberOfLineFinder.getTotalNumberOfLinesUsingScanner;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingApacheCommonsIO;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingBufferedReader;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingGoogleGuava;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingLineNumberReader;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFileChannel;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFiles;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingNIOFilesReadAllLines;
+import static com.baeldung.file.NumberOfLineFinder.getTotalNumberOfLinesUsingScanner;
 import static org.junit.Assert.assertEquals;
 
 import org.junit.Test;
@@ -39,6 +40,12 @@ public class NumberOfLineFinderUnitTest {
         assertEquals(ACTUAL_LINE_COUNT, lines);
     }
 
+    @Test
+    public void whenUsingNIOFilesReadAllLines_thenReturnTotalNumberOfLines() {
+        int lines = getTotalNumberOfLinesUsingNIOFilesReadAllLines(INPUT_FILE_NAME);
+        assertEquals(ACTUAL_LINE_COUNT, lines);
+    }
+
     @Test
     public void whenUsingNIOFileChannel_thenReturnTotalNumberOfLines() {
         int lines = getTotalNumberOfLinesUsingNIOFileChannel(INPUT_FILE_NAME);

core-java-modules/core-java-os/README.md

@@ -7,4 +7,4 @@ This module uses Java 9, so make sure to have the JDK 9 installed to run it.
 - [Java 9 Process API Improvements](http://www.baeldung.com/java-9-process-api)
 - [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
 - [Guide to java.lang.ProcessBuilder API](https://www.baeldung.com/java-lang-processbuilder-api)
-
+- [Get the Current Working Directory in Java](https://www.baeldung.com/java-current-directory)

core-java-modules/core-java-security/README.md

@@ -10,3 +10,4 @@
 - [SSL Handshake Failures](https://www.baeldung.com/java-ssl-handshake-failures)
 - [SHA-256 and SHA3-256 Hashing in Java](https://www.baeldung.com/sha-256-hashing-java)
 - [Enabling TLS v1.2 in Java 7](https://www.baeldung.com/java-7-tls-v12)
+- [The Java SecureRandom Class](https://www.baeldung.com/java-secure-random)

core-java-modules/core-java-security/src/test/java/com/baeldung/jgss/JgssIntegrationTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.jgss;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import javax.security.sasl.SaslException;
+
+import org.ietf.jgss.GSSContext;
+import org.ietf.jgss.GSSCredential;
+import org.ietf.jgss.GSSException;
+import org.ietf.jgss.GSSManager;
+import org.ietf.jgss.GSSName;
+import org.ietf.jgss.MessageProp;
+import org.ietf.jgss.Oid;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Ignore;
+import org.junit.Test;
+
+@Ignore
+public class JgssIntegrationTest {
+
+    private static final String SERVER_PRINCIPAL = "HTTP/localhost@EXAMPLE.COM";
+    private static final String MECHANISM = "1.2.840.113554.1.2.2";
+
+    GSSContext serverContext;
+    GSSContext clientContext;
+
+    @Before
+    public void setUp() throws SaslException, GSSException {
+        GSSManager manager = GSSManager.getInstance();
+        serverContext = manager.createContext((GSSCredential) null);
+        String serverPrinciple = SERVER_PRINCIPAL;
+        GSSName serverName = manager.createName(serverPrinciple, null);
+        Oid krb5Oid = new Oid(MECHANISM);
+        clientContext = manager.createContext(serverName, krb5Oid, (GSSCredential) null, GSSContext.DEFAULT_LIFETIME);
+        clientContext.requestMutualAuth(true);
+        clientContext.requestConf(true);
+        clientContext.requestInteg(true);
+    }
+
+    @Test
+    public void givenCredential_whenStarted_thenAutenticationWorks() throws SaslException, GSSException {
+        byte[] serverToken;
+        byte[] clientToken;
+
+        // On the client-side
+        clientToken = clientContext.initSecContext(new byte[0], 0, 0);
+        // sendToServer(clientToken); // This is supposed to be send over the network
+
+        // On the server-side
+        serverToken = serverContext.acceptSecContext(clientToken, 0, clientToken.length);
+        // sendToClient(serverToken); // This is supposed to be send over the network
+
+        // Back on the client-side
+        clientContext.initSecContext(serverToken, 0, serverToken.length);
+
+        assertTrue(serverContext.isEstablished());
+        assertTrue(clientContext.isEstablished());
+    }
+
+    @Test
+    public void givenContext_whenStarted_thenSecurityWorks() throws SaslException, GSSException {
+        // On the client-side
+        byte[] messageBytes = "Baeldung".getBytes();
+        MessageProp clientProp = new MessageProp(0, true);
+        byte[] clientToken = clientContext.wrap(messageBytes, 0, messageBytes.length, clientProp);
+        // sendToServer(clientToken); // This is supposed to be send over the network
+
+        // On the server-side
+        MessageProp serverProp = new MessageProp(0, false);
+        byte[] bytes = serverContext.unwrap(clientToken, 0, clientToken.length, serverProp);
+        String string = new String(bytes);
+
+        assertEquals("Baeldung", string);
+    }
+
+    @After
+    public void tearDown() throws SaslException, GSSException {
+        serverContext.dispose();
+        clientContext.dispose();
+    }
+
+}

core-java-modules/pom.xml

@@ -17,6 +17,7 @@
         <module>pre-jpms</module>
         <module>core-java-exceptions</module>
         <module>core-java-optional</module>
+        <module>core-java-lang-operators</module>
         <module>core-java-networking-2</module>
     </modules>
     

data-structures/README.md

@@ -1,4 +1,5 @@
 ## Relevant articles:
 
-[The Trie Data Structure in Java](https://www.baeldung.com/trie-java)
-[Implementing a Binary Tree in Java](https://www.baeldung.com/java-binary-tree)
+- [The Trie Data Structure in Java](https://www.baeldung.com/trie-java)
+- [Implementing a Binary Tree in Java](https://www.baeldung.com/java-binary-tree)
+- [Depth First Search in Java](https://www.baeldung.com/java-depth-first-search)

httpclient-simple/pom.xml

@@ -21,12 +21,12 @@
         <dependency>
             <groupId>org.springframework.security</groupId>
             <artifactId>spring-security-web</artifactId>
-            <version>${spring.version}</version>
+            <version>${spring-security.version}</version>
         </dependency>
         <dependency>
             <groupId>org.springframework.security</groupId>
             <artifactId>spring-security-config</artifactId>
-            <version>${spring.version}</version>
+            <version>${spring-security.version}</version>
         </dependency>
 
         <!-- Spring -->

intelliJ/intelliJ-formatter.xml

@@ -1,19 +1,15 @@
-<code_scheme name="baeldung">
+<code_scheme name="baeldung-formatter" version="173">
   <option name="RIGHT_MARGIN" value="260" />
-  <option name="ENABLE_JAVADOC_FORMATTING" value="false" />
   <option name="FORMATTER_TAGS_ENABLED" value="true" />
   <JavaCodeStyleSettings>
-    <option name="SPACE_AFTER_CLOSING_ANGLE_BRACKET_IN_TYPE_ARGUMENT" value="true" />
-    <option name="DO_NOT_WRAP_AFTER_SINGLE_ANNOTATION" value="true" />
-    <option name="ALIGN_MULTILINE_ANNOTATION_PARAMETERS" value="true" />
+    <option name="CLASS_COUNT_TO_USE_IMPORT_ON_DEMAND" value="500" />
+    <option name="NAMES_COUNT_TO_USE_IMPORT_ON_DEMAND" value="300" />
+    <option name="ENABLE_JAVADOC_FORMATTING" value="false" />
   </JavaCodeStyleSettings>
-  <JetCodeStyleSettings>
-    <option name="NAME_COUNT_TO_USE_STAR_IMPORT" value="99" />
-    <option name="NAME_COUNT_TO_USE_STAR_IMPORT_FOR_MEMBERS" value="99" />
-  </JetCodeStyleSettings>
   <codeStyleSettings language="JAVA">
     <option name="KEEP_LINE_BREAKS" value="false" />
     <option name="KEEP_FIRST_COLUMN_COMMENT" value="false" />
+    <option name="KEEP_CONTROL_STATEMENT_IN_ONE_LINE" value="false" />
     <option name="KEEP_BLANK_LINES_IN_DECLARATIONS" value="1" />
     <option name="KEEP_BLANK_LINES_IN_CODE" value="1" />
     <option name="KEEP_BLANK_LINES_BEFORE_RBRACE" value="1" />
@@ -29,19 +25,18 @@
     <option name="THROWS_LIST_WRAP" value="1" />
     <option name="EXTENDS_KEYWORD_WRAP" value="1" />
     <option name="THROWS_KEYWORD_WRAP" value="1" />
-    <option name="METHOD_CALL_CHAIN_WRAP" value="2" />
-    <option name="WRAP_FIRST_METHOD_IN_CALL_CHAIN" value="true" />
+    <option name="METHOD_CALL_CHAIN_WRAP" value="5" />
     <option name="BINARY_OPERATION_WRAP" value="1" />
     <option name="BINARY_OPERATION_SIGN_ON_NEXT_LINE" value="true" />
     <option name="TERNARY_OPERATION_WRAP" value="5" />
-    <option name="TERNARY_OPERATION_SIGNS_ON_NEXT_LINE" value="true" />
     <option name="ARRAY_INITIALIZER_WRAP" value="1" />
-    <option name="ARRAY_INITIALIZER_LBRACE_ON_NEXT_LINE" value="true" />
-    <option name="ARRAY_INITIALIZER_RBRACE_ON_NEXT_LINE" value="true" />
-    <option name="PLACE_ASSIGNMENT_SIGN_ON_NEXT_LINE" value="true" />
+    <option name="METHOD_ANNOTATION_WRAP" value="0" />
+    <option name="CLASS_ANNOTATION_WRAP" value="0" />
+    <option name="FIELD_ANNOTATION_WRAP" value="0" />
     <indentOptions>
-      <option name="CONTINUATION_INDENT_SIZE" value="2" />
-      <option name="TAB_SIZE" value="8" />
+      <option name="INDENT_SIZE" value="8" />
+      <option name="CONTINUATION_INDENT_SIZE" value="4" />
+      <option name="SMART_TABS" value="true" />
     </indentOptions>
   </codeStyleSettings>
 </code_scheme>

jackson-2/README.md

@@ -10,3 +10,4 @@ The "REST With Spring" Classes: http://bit.ly/restwithspring
 - [How to Process YAML with Jackson](https://www.baeldung.com/jackson-yaml)
 - [Working with Tree Model Nodes in Jackson](https://www.baeldung.com/jackson-json-node-tree-model)
 - [Converting JSON to CSV in Java](https://www.baeldung.com/java-converting-json-to-csv)
+- [Compare Two JSON Objects with Jackson](https://www.baeldung.com/jackson-compare-two-json-objects)

jackson-2/src/main/java/com/baeldung/jackson/entities/File.java

@@ -0,0 +1,25 @@
+package com.baeldung.jackson.entities;
+
+public class File {
+
+    private Long id;
+
+    private String name;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/entities/Folder.java

@@ -0,0 +1,82 @@
+package com.baeldung.jackson.entities;
+
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.List;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+
+public class Folder {
+
+    private Long id;
+
+    private String name;
+
+    private String owner;
+
+    private Date created;
+
+    private Date modified;
+
+    private Date lastAccess;
+
+    @JsonIgnore
+    private List<File> files = new ArrayList<>();
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getOwner() {
+        return owner;
+    }
+
+    public void setOwner(String owner) {
+        this.owner = owner;
+    }
+
+    public Date getCreated() {
+        return created;
+    }
+
+    public void setCreated(Date created) {
+        this.created = created;
+    }
+
+    public Date getModified() {
+        return modified;
+    }
+
+    public void setModified(Date modified) {
+        this.modified = modified;
+    }
+
+    public Date getLastAccess() {
+        return lastAccess;
+    }
+
+    public void setLastAccess(Date lastAccess) {
+        this.lastAccess = lastAccess;
+    }
+
+    public List<File> getFiles() {
+        return files;
+    }
+
+    public void setFiles(List<File> files) {
+        this.files = files;
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderBeanSerializerModifier.java

@@ -0,0 +1,21 @@
+package com.baeldung.jackson.serialization.custom.serializer;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.databind.BeanDescription;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializationConfig;
+import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
+
+public class FolderBeanSerializerModifier extends BeanSerializerModifier {
+
+    @Override
+    public JsonSerializer<?> modifySerializer(SerializationConfig config, BeanDescription beanDesc, JsonSerializer<?> serializer) {
+
+        if (beanDesc.getBeanClass().equals(Folder.class)) {
+            return new FolderSerializerWithDefaultSerializerStored((JsonSerializer<Object>) serializer);
+        }
+
+        return serializer;
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializer.java

@@ -0,0 +1,36 @@
+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.File;
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializer extends StdSerializer<Folder> {
+
+    public FolderSerializer() {
+        super(Folder.class);
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        gen.writeArrayFieldStart("files");
+        for (File file : value.getFiles()) {
+            gen.writeStartObject();
+            gen.writeNumberField("id", file.getId());
+            gen.writeStringField("name", file.getName());
+            gen.writeEndObject();
+        }
+        gen.writeEndArray();
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializerWithCallingOwnSerializer.java

@@ -0,0 +1,30 @@
+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializerWithCallingOwnSerializer extends StdSerializer<Folder> {
+
+    public FolderSerializerWithCallingOwnSerializer() {
+        super(Folder.class);
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        provider.defaultSerializeField("files", value.getFiles(), gen);
+
+        provider.defaultSerializeField("details", value, gen);
+
+        gen.writeEndObject();
+
+    }
+
+}

jackson-2/src/main/java/com/baeldung/jackson/serialization/custom/serializer/FolderSerializerWithDefaultSerializerStored.java

@@ -0,0 +1,35 @@
+package com.baeldung.jackson.serialization.custom.serializer;
+
+import java.io.IOException;
+
+import com.baeldung.jackson.entities.Folder;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class FolderSerializerWithDefaultSerializerStored extends StdSerializer<Folder> {
+
+    private final JsonSerializer<Object> defaultSerializer;
+
+    public FolderSerializerWithDefaultSerializerStored(JsonSerializer<Object> defaultSerializer) {
+        super(Folder.class);
+        this.defaultSerializer = defaultSerializer;
+    }
+
+    @Override
+    public void serialize(Folder value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+
+        gen.writeStartObject();
+        gen.writeStringField("name", value.getName());
+
+        provider.defaultSerializeField("files", value.getFiles(), gen);
+
+        gen.writeFieldName("details");
+        defaultSerializer.serialize(value, gen, provider);
+
+        gen.writeEndObject();
+
+    }
+
+}