[BAEL-3348] Moved code to algorithm-4

java-streams-2/README.md

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+## Java Streams Cookbooks and Examples
+
+This module contains articles about the Stream API in Java.
+
+### Relevant Articles:
+- [Guide to Stream.reduce()](https://www.baeldung.com/java-stream-reduce)
+- [How to Break from Java Stream forEach](https://www.baeldung.com/java-break-stream-foreach)
+- [Java IntStream Conversions](https://www.baeldung.com/java-intstream-convert)
+- More articles: [[<-- prev]](/java-streams)

java-streams-2/pom.xml

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+<?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.javastreams2</groupId>
+    <artifactId>java-streams-2</artifactId>
+    <version>1.0</version>
+    <name>java-streams-2</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>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+            <type>jar</type>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+	
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.9</maven.compiler.source>
+        <maven.compiler.target>1.9</maven.compiler.target>
+        <assertj.version>3.11.1</assertj.version>
+    </properties>
+</project>

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomForEach.java

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+package com.baeldung.breakforeach;
+
+import java.util.Spliterator;
+import java.util.function.BiConsumer;
+import java.util.stream.Stream;
+
+public class CustomForEach {
+
+    public static class Breaker {
+        private boolean shouldBreak = false;
+
+        public void stop() {
+            shouldBreak = true;
+        }
+
+        boolean get() {
+            return shouldBreak;
+        }
+    }
+
+    public static <T> void forEach(Stream<T> stream, BiConsumer<T, Breaker> consumer) {
+        Spliterator<T> spliterator = stream.spliterator();
+        boolean hadNext = true;
+        Breaker breaker = new Breaker();
+
+        while (hadNext && !breaker.get()) {
+            hadNext = spliterator.tryAdvance(elem -> {
+                consumer.accept(elem, breaker);
+            });
+        }
+    }
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomSpliterator.java

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+package com.baeldung.breakforeach;
+
+import java.util.Spliterator;
+import java.util.Spliterators;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+
+public class CustomSpliterator<T> extends Spliterators.AbstractSpliterator<T> {
+
+    private Spliterator<T> splitr;
+    private Predicate<T> predicate;
+    private boolean isMatched = true;
+
+    public CustomSpliterator(Spliterator<T> splitr, Predicate<T> predicate) {
+        super(splitr.estimateSize(), 0);
+        this.splitr = splitr;
+        this.predicate = predicate;
+    }
+
+    @Override
+    public boolean tryAdvance(Consumer<? super T> consumer) {
+        boolean hadNext = splitr.tryAdvance(elem -> {
+            if (predicate.test(elem) && isMatched) {
+                consumer.accept(elem);
+            } else {
+                isMatched = false;
+            }
+        });
+        return hadNext && isMatched;
+    }
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/CustomTakeWhile.java

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+package com.baeldung.breakforeach;
+
+import java.util.function.Predicate;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+public class CustomTakeWhile {
+
+    public static <T> Stream<T> takeWhile(Stream<T> stream, Predicate<T> predicate) {
+        CustomSpliterator<T> customSpliterator = new CustomSpliterator<>(stream.spliterator(), predicate);
+        return StreamSupport.stream(customSpliterator, false);
+    }
+
+}

java-streams-2/src/main/java/com/baeldung/breakforeach/TakeWhileExample.java

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+package com.baeldung.breakforeach;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+
+public class TakeWhileExample {
+
+    public static void takeWhileJava9() {
+        Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck")
+            .takeWhile(n -> n.length() % 2 != 0)
+            .forEach(System.out::println); // cat, dog
+    }
+
+    public static void plainForLoopWithBreak() {
+        List<String> list = asList("cat", "dog", "elephant", "fox", "rabbit", "duck");
+        for (int i = 0; i < list.size(); i++) {
+            String item = list.get(i);
+            if (item.length() % 2 == 0) {
+                break;
+            }
+            System.out.println(item);
+        }
+    }
+}

java-streams-2/src/main/java/com/baeldung/reduce/application/Application.java

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+package com.baeldung.reduce.application;
+
+import com.baeldung.reduce.entities.User;
+import com.baeldung.reduce.utilities.NumberUtils;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Application {
+
+    public static void main(String[] args) {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        int result1 = numbers.stream().reduce(0, (subtotal, element) -> subtotal + element);
+        System.out.println(result1);
+        
+        int result2 = numbers.stream().reduce(0, Integer::sum);
+        System.out.println(result2);
+
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        String result3 = letters.stream().reduce("", (partialString, element) -> partialString + element);
+        System.out.println(result3);
+        
+        String result4 = letters.stream().reduce("", String::concat);
+        System.out.println(result4);
+
+        String result5 = letters.stream().reduce("", (partialString, element) -> partialString.toUpperCase() + element.toUpperCase());
+        System.out.println(result5);
+        
+        List<User> users = Arrays.asList(new User("John", 30), new User("Julie", 35));
+        int result6 = users.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        System.out.println(result6);
+        
+        String result7 = letters.parallelStream().reduce("", String::concat);
+        System.out.println(result7);
+        
+        int result8 = users.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        System.out.println(result8);
+    }    
+}

java-streams-2/src/main/java/com/baeldung/reduce/benchmarks/JMHStreamReduceBenchMark.java

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+package com.baeldung.reduce.benchmarks;
+
+import com.baeldung.reduce.entities.User;
+import java.util.ArrayList;
+import java.util.List;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.RunnerException;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+@State(Scope.Thread)
+@BenchmarkMode(Mode.AverageTime)
+public class JMHStreamReduceBenchMark {
+    
+    private final List<User> userList = createUsers();
+
+    public static void main(String[] args) throws RunnerException {
+        
+        Options options = new OptionsBuilder()
+                .include(JMHStreamReduceBenchMark.class.getSimpleName()).threads(1)
+                .forks(1).shouldFailOnError(true).shouldDoGC(true)
+                .jvmArgs("-server").build();
+        new Runner(options).run();
+    }
+    
+    private List<User> createUsers() {
+        List<User> users = new ArrayList<>();
+        for (int i = 0; i <= 1000000; i++) {
+            users.add(new User("John" + i, i));
+        }
+        return users;
+    }
+
+    @Benchmark
+    public Integer executeReduceOnParallelizedStream() {
+        return this.userList
+                .parallelStream()
+                .reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+    }
+
+    @Benchmark
+    public Integer executeReduceOnSequentialStream() {
+        return this.userList
+                .stream()
+                .reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+    }
+}

java-streams-2/src/main/java/com/baeldung/reduce/entities/User.java

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+package com.baeldung.reduce.entities;
+
+public class User {
+
+    private final String name;
+    private final int age;
+
+    public User(String name, int age) {
+        this.name = name;
+        this.age = age;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+    
+    @Override
+    public String toString() {
+        return "User{" + "name=" + name + ", age=" + age + '}';
+    }
+}

java-streams-2/src/main/java/com/baeldung/reduce/utilities/NumberUtils.java

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+package com.baeldung.reduce.utilities;
+
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+public abstract class NumberUtils {
+
+    private static final Logger LOGGER = Logger.getLogger(NumberUtils.class.getName());
+
+    public static int divideListElements(List<Integer> values, Integer divider) {
+        return values.stream()
+                .reduce(0, (a, b) -> {
+                    try {
+                        return a / divider + b / divider;
+                    } catch (ArithmeticException e) {
+                        LOGGER.log(Level.INFO, "Arithmetic Exception: Division by Zero");
+                    }
+                    return 0;
+                });
+    }
+    
+    public static int divideListElementsWithExtractedTryCatchBlock(List<Integer> values, int divider) {
+        return values.stream().reduce(0, (a, b) -> divide(a, divider) + divide(b, divider));
+    }
+    
+    public static int divideListElementsWithApplyFunctionMethod(List<Integer> values, int divider) {
+        BiFunction<Integer, Integer, Integer> division = (a, b) -> a / b;
+        return values.stream().reduce(0, (a, b) -> applyFunction(division, a, divider) + applyFunction(division, b, divider));
+    }
+    
+    private static int divide(int value, int factor) {
+        int result = 0;
+        try {
+            result = value / factor;
+        } catch (ArithmeticException e) {
+            LOGGER.log(Level.INFO, "Arithmetic Exception: Division by Zero");
+        }
+        return result;
+    }
+    
+    private static int applyFunction(BiFunction<Integer, Integer, Integer> function, int a, int b) {
+        try {
+            return function.apply(a, b);
+        }
+        catch(Exception e) {
+            LOGGER.log(Level.INFO, "Exception thrown!");
+        }
+        return 0;
+    }
+}

java-streams-2/src/test/java/com/baeldung/breakforeach/BreakFromStreamForEachUnitTest.java

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+package com.baeldung.breakforeach;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+
+public class BreakFromStreamForEachUnitTest {
+
+    @Test
+    public void whenCustomTakeWhileIsCalled_ThenCorrectItemsAreReturned() {
+        Stream<String> initialStream = Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck");
+
+        List<String> result = CustomTakeWhile.takeWhile(initialStream, x -> x.length() % 2 != 0)
+                .collect(Collectors.toList());
+
+        assertEquals(asList("cat", "dog"), result);
+    }
+
+    @Test
+    public void whenCustomForEachIsCalled_ThenCorrectItemsAreReturned() {
+        Stream<String> initialStream = Stream.of("cat", "dog", "elephant", "fox", "rabbit", "duck");
+        List<String> result = new ArrayList<>();
+
+        CustomForEach.forEach(initialStream, (elem, breaker) -> {
+            if (elem.length() % 2 == 0) {
+                breaker.stop();
+            } else {
+                result.add(elem);
+            }
+        });
+
+        assertEquals(asList("cat", "dog"), result);
+    }
+
+}

java-streams-2/src/test/java/com/baeldung/convert/intstreams/IntStreamsConversionsUnitTest.java

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+package com.baeldung.convert.intstreams;
+
+import org.junit.Test;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class IntStreamsConversionsUnitTest {
+
+    @Test
+    public void intStreamToArray() {
+        int[] first50EvenNumbers = IntStream.iterate(0, i -> i + 2)
+                .limit(50)
+                .toArray();
+
+        assertThat(first50EvenNumbers).hasSize(50);
+        assertThat(first50EvenNumbers[2]).isEqualTo(4);
+    }
+
+    @Test
+    public void intStreamToList() {
+        List<Integer> first50IntegerNumbers = IntStream.range(0, 50)
+                .boxed()
+                .collect(Collectors.toList());
+
+        assertThat(first50IntegerNumbers).hasSize(50);
+        assertThat(first50IntegerNumbers.get(2)).isEqualTo(2);
+    }
+
+    @Test
+    public void intStreamToString() {
+        String first3numbers = IntStream.of(0, 1, 2)
+                .mapToObj(String::valueOf)
+                .collect(Collectors.joining(", ", "[", "]"));
+
+        assertThat(first3numbers).isEqualTo("[0, 1, 2]");
+    }
+}

java-streams-2/src/test/java/com/baeldung/reduce/tests/StreamReduceUnitTest.java

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+package com.baeldung.reduce.tests;
+
+import com.baeldung.reduce.entities.User;
+import com.baeldung.reduce.utilities.NumberUtils;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class StreamReduceUnitTest {
+
+    @Test
+    public void givenIntegerList_whenReduceWithSumAccumulatorLambda_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        int result = numbers.stream().reduce(0, (subtotal, element) -> subtotal + element);
+        assertThat(result).isEqualTo(21);
+    }
+
+    @Test
+    public void givenIntegerList_whenReduceWithSumAccumulatorMethodReference_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        int result = numbers.stream().reduce(0, Integer::sum);
+        assertThat(result).isEqualTo(21);
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithConcatenatorAccumulatorLambda_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        String result = letters.stream().reduce("", (partialString, element) -> partialString + element);
+        assertThat(result).isEqualTo("abcde");
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithConcatenatorAccumulatorMethodReference_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        String result = letters.stream().reduce("", String::concat);
+        assertThat(result).isEqualTo("abcde");
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithUppercaseConcatenatorAccumulator_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        String result = letters.stream().reduce("", (partialString, element) -> partialString.toUpperCase() + element.toUpperCase());
+        assertThat(result).isEqualTo("ABCDE");
+    }
+
+    @Test
+    public void givenUserList_whenReduceWithAgeAccumulatorAndSumCombiner_thenCorrect() {
+        List<User> users = Arrays.asList(new User("John", 30), new User("Julie", 35));
+        int result = users.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
+        assertThat(result).isEqualTo(65);
+    }
+
+    @Test
+    public void givenStringList_whenReduceWithParallelStream_thenCorrect() {
+        List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
+        String result = letters.parallelStream().reduce("", String::concat);
+        assertThat(result).isEqualTo("abcde");
+    }
+
+    @Test
+    public void givenNumberUtilsClass_whenCalledDivideListElements_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        assertThat(NumberUtils.divideListElements(numbers, 1)).isEqualTo(21);
+    }
+
+    @Test
+    public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlock_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 1)).isEqualTo(21);
+    }
+
+    @Test
+    public void givenStream_whneCalleddivideListElementsWithApplyFunctionMethod_thenCorrect() {
+        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
+        assertThat(NumberUtils.divideListElementsWithApplyFunctionMethod(numbers, 1)).isEqualTo(21);
+    }
+}