BAEL-1473 Intoduction to Spliterator in Java (#3400)

core-java-8/src/main/java/com/baeldung/spliteratorAPI/Article.java

@@ -0,0 +1,44 @@
+package com.baeldung.spliteratorAPI;
+
+import java.util.List;
+
+public class Article {
+    private List<Author> listOfAuthors;
+    private int id;
+    private String name;
+
+    public Article(String name) {
+        this.name = name;
+    }
+
+    public Article(List<Author> listOfAuthors, int id) {
+        super();
+        this.listOfAuthors = listOfAuthors;
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public List<Author> getListOfAuthors() {
+        return listOfAuthors;
+    }
+
+    public void setListOfAuthors(List<Author> listOfAuthors) {
+        this.listOfAuthors = listOfAuthors;
+    }
+
+}

core-java-8/src/main/java/com/baeldung/spliteratorAPI/Author.java

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+package com.baeldung.spliteratorAPI;
+
+public class Author {
+    private String name;
+    private int relatedArticleId;
+
+    public Author(String name, int relatedArticleId) {
+        this.name = name;
+        this.relatedArticleId = relatedArticleId;
+    }
+
+    public int getRelatedArticleId() {
+        return relatedArticleId;
+    }
+
+    public void setRelatedArticleId(int relatedArticleId) {
+        this.relatedArticleId = relatedArticleId;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public String toString() {
+        return "[name: " + name + ", relatedId: " + relatedArticleId + "]";
+    }
+}
+

core-java-8/src/main/java/com/baeldung/spliteratorAPI/Executor.java

@@ -0,0 +1,45 @@
+package com.baeldung.spliteratorAPI;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Spliterator;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+public class Executor {
+	public void executeCustomSpliterator() {
+        Article article = new Article(Arrays.asList(new Author("Ahmad", 0), new Author("Eugen", 0), new Author("Alice", 1), new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1),
+            new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0), new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0), new Author("Alice", 1), new Author("Mike", 0),
+            new Author("Alice", 1), new Author("Mike", 0), new Author("Michał", 0), new Author("Loredana", 1)), 0);
+        Stream<Author> stream = IntStream.range(0, article.getListOfAuthors()
+            .size())
+            .mapToObj(article.getListOfAuthors()::get);
+        System.out.println("count= " + countAutors(stream.parallel()));
+        Spliterator<Author> spliterator = new RelatedAuthorSpliterator(article.getListOfAuthors());
+        Stream<Author> stream2 = StreamSupport.stream(spliterator, true);
+        System.out.println("count= " + countAutors(stream2.parallel()));
+    }
+
+    public void executeSpliterator() {
+        Spliterator<Article> split1 = generateElements().spliterator();
+        Spliterator<Article> split2 = split1.trySplit();
+        ExecutorService service = Executors.newCachedThreadPool();
+        service.execute(new Task(split1));
+        service.execute(new Task(split2));
+    }
+
+    private static int countAutors(Stream<Author> stream) {
+        RelatedAuthorCounter wordCounter = stream.reduce(new RelatedAuthorCounter(0, true), RelatedAuthorCounter::accumulate, RelatedAuthorCounter::combine);
+        return wordCounter.getCounter();
+    }
+
+    private List<Article> generateElements() {
+        return Stream.generate(() -> new Article("Java"))
+            .limit(35000)
+            .collect(Collectors.toList());
+    }
+}

core-java-8/src/main/java/com/baeldung/spliteratorAPI/RelatedAuthorCounter.java

@@ -0,0 +1,27 @@
+package com.baeldung.spliteratorAPI;
+
+public class RelatedAuthorCounter {
+    private final int counter;
+    private final boolean isRelated;
+
+    public RelatedAuthorCounter(int counter, boolean isRelated) {
+        this.counter = counter;
+        this.isRelated = isRelated;
+    }
+
+    public RelatedAuthorCounter accumulate(Author author) {
+        if (author.getRelatedArticleId() == 0) {
+            return isRelated ? this : new RelatedAuthorCounter(counter, true);
+        } else {
+            return isRelated ? new RelatedAuthorCounter(counter + 1, false) : this;
+        }
+    }
+
+    public RelatedAuthorCounter combine(RelatedAuthorCounter RelatedAuthorCounter) {
+        return new RelatedAuthorCounter(counter + RelatedAuthorCounter.counter, RelatedAuthorCounter.isRelated);
+    }
+
+    public int getCounter() {
+        return counter;
+    }
+}

core-java-8/src/main/java/com/baeldung/spliteratorAPI/RelatedAuthorSpliterator.java

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+package com.baeldung.spliteratorAPI;
+
+import java.util.List;
+import java.util.Spliterator;
+import java.util.function.Consumer;
+
+public class RelatedAuthorSpliterator implements Spliterator<Author> {
+    private final List<Author> list;
+    private int current = 0;
+
+    public RelatedAuthorSpliterator(List<Author> list) {
+        this.list = list;
+    }
+
+    @Override
+    public boolean tryAdvance(Consumer<? super Author> action) {
+        action.accept(list.get(current++));
+        return current < list.size();
+    }
+
+    @Override
+    public Spliterator<Author> trySplit() {
+        int currentSize = list.size() - current;
+        if (currentSize < 10) {
+            return null;
+        }
+        for (int splitPos = currentSize / 2 + current; splitPos < list.size(); splitPos++) {
+            if (list.get(splitPos)
+                .getRelatedArticleId() == 0) {
+                Spliterator<Author> spliterator = new RelatedAuthorSpliterator(list.subList(current, splitPos));
+                current = splitPos;
+                return spliterator;
+            }
+        }
+        return null;
+    }
+
+    @Override
+    public long estimateSize() {
+        return list.size() - current;
+    }
+
+    @Override
+    public int characteristics() {
+        return SIZED + CONCURRENT;
+    }
+}

core-java-8/src/main/java/com/baeldung/spliteratorAPI/Task.java

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+package com.baeldung.spliteratorAPI;
+
+import java.util.Spliterator;
+
+public class Task implements Runnable {
+    private Spliterator<Article> spliterator;
+    private final static String SUFFIX = "- published by Baeldung";
+
+    public Task(Spliterator<Article> spliterator) {
+        this.spliterator = spliterator;
+    }
+
+    @Override
+    public void run() {
+        int current = 0;
+        while (spliterator.tryAdvance(article -> {
+            article.setName(article.getName()
+                .concat(SUFFIX));
+        })) {
+            current++;
+        }
+        ;
+        System.out.println(Thread.currentThread()
+            .getName() + ":" + current);
+    }
+}