From d160a09b014bd2204c26bcaac8752784e9c87423 Mon Sep 17 00:00:00 2001
From: Daniel Strmecki <daniel.strmecki@gmail.com>
Date: Mon, 3 May 2021 11:18:02 +0200
Subject: [PATCH] BAEL-4876: Parallel stream examples added

---
 core-java-modules/core-java-streams-3/pom.xml |  1 +
 .../streams/parallel/ParallelStream.java      | 14 ++++++
 .../streams/parallel/SequentialStream.java    | 14 ++++++
 .../streams/parallel/ForkJoinUnitTest.java    | 45 +++++++++++++++++++
 4 files changed, 74 insertions(+)
 create mode 100644 core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/ParallelStream.java
 create mode 100644 core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/SequentialStream.java
 create mode 100644 core-java-modules/core-java-streams-3/src/test/java/com/baeldung/streams/parallel/ForkJoinUnitTest.java

diff --git a/core-java-modules/core-java-streams-3/pom.xml b/core-java-modules/core-java-streams-3/pom.xml
index 6597c999d8..2ec2fa7c48 100644
--- a/core-java-modules/core-java-streams-3/pom.xml
+++ b/core-java-modules/core-java-streams-3/pom.xml
@@ -47,6 +47,7 @@
     </build>
 
     <properties>
+        <lombok.version>1.18.20</lombok.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>
     </properties>
diff --git a/core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/ParallelStream.java b/core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/ParallelStream.java
new file mode 100644
index 0000000000..deeaf9ed59
--- /dev/null
+++ b/core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/ParallelStream.java
@@ -0,0 +1,14 @@
+package com.baeldung.streams.parallel;
+
+import java.util.List;
+
+public class ParallelStream {
+
+    public static void main(String[] args) {
+        List<Integer> listOfNumbers = List.of(1, 2, 3, 4);
+        listOfNumbers.parallelStream().forEach(number ->
+          System.out.println(number + " " + Thread.currentThread().getName())
+        );
+    }
+
+}
diff --git a/core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/SequentialStream.java b/core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/SequentialStream.java
new file mode 100644
index 0000000000..0e9c42640b
--- /dev/null
+++ b/core-java-modules/core-java-streams-3/src/main/java/com/baeldung/streams/parallel/SequentialStream.java
@@ -0,0 +1,14 @@
+package com.baeldung.streams.parallel;
+
+import java.util.List;
+
+public class SequentialStream {
+
+    public static void main(String[] args) {
+        List<Integer> listOfNumbers = List.of(1, 2, 3, 4);
+        listOfNumbers.stream().forEach(number ->
+          System.out.println(number + " " + Thread.currentThread().getName())
+        );
+    }
+
+}
diff --git a/core-java-modules/core-java-streams-3/src/test/java/com/baeldung/streams/parallel/ForkJoinUnitTest.java b/core-java-modules/core-java-streams-3/src/test/java/com/baeldung/streams/parallel/ForkJoinUnitTest.java
new file mode 100644
index 0000000000..12cf5ceb16
--- /dev/null
+++ b/core-java-modules/core-java-streams-3/src/test/java/com/baeldung/streams/parallel/ForkJoinUnitTest.java
@@ -0,0 +1,45 @@
+package com.baeldung.streams.parallel;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ForkJoinPool;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class ForkJoinUnitTest {
+
+    @Test
+    void givenSequentialStreamOfNumbers_whenReducingSumWithIdentityFive_thenResultIsCorrect() {
+        List<Integer> listOfNumbers = List.of(1, 2, 3, 4);
+        int sum = listOfNumbers.stream().reduce(5, Integer::sum);
+        assertThat(sum).isEqualTo(15);
+    }
+
+    @Test
+    void givenParallelStreamOfNumbers_whenReducingSumWithIdentityFive_thenResultIsNotCorrect() {
+        List<Integer> listOfNumbers = List.of(1, 2, 3, 4);
+        int sum = listOfNumbers.parallelStream().reduce(5, Integer::sum);
+        assertThat(sum).isNotEqualTo(15);
+    }
+
+    @Test
+    void givenParallelStreamOfNumbers_whenReducingSumWithIdentityZero_thenResultIsCorrect() {
+        List<Integer> listOfNumbers = List.of(1, 2, 3, 4);
+        int sum = listOfNumbers.parallelStream().reduce(0, Integer::sum) + 5;
+        assertThat(sum).isEqualTo(15);
+    }
+
+    @Test
+    public void givenParallelStreamOfNumbers_whenUsingCustomThreadPool_thenResultIsCorrect()
+      throws InterruptedException, ExecutionException {
+        List<Integer> listOfNumbers = List.of(1, 2, 3, 4);
+        ForkJoinPool customThreadPool = new ForkJoinPool(4);
+        int sum = customThreadPool.submit(
+          () -> listOfNumbers.parallelStream().reduce(0, Integer::sum)).get();
+        customThreadPool.shutdown();
+        assertThat(sum).isEqualTo(10);
+    }
+
+}