BAEL-2837 Add sample Set operations in Java (#6697)

* BAEL-2837: Add sample set operations in Java

* BAEL-2837 add new module core-java-collections-set

* BAEL-2837 Updated readme.md file

* BAEL-2837 Tidy dependencies in pom.xml

* BAEL-2837 tidy white space in pom.xml

* BAEL-2837 Rename unit test class

* BAEL-2837 Removed unused logback-xml

core-java-collections-set/README.md

@@ -0,0 +1,6 @@
+=========
+
+## Core Java Sets Cookbooks and Examples
+
+### Relevant Articles: 
+- [Set Operations in Java](http://www.baeldung.com/set-operations-in-java)

core-java-collections-set/pom.xml

@@ -0,0 +1,33 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-collections-set</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-collections-set</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>com.google.guava</groupId>
+        <artifactId>guava</artifactId>
+        <version>${guava.version}</version>
+    </dependency>
+    <dependency>
+        <groupId>org.apache.commons</groupId>
+        <artifactId>commons-collections4</artifactId>
+        <version>${commons-collections4.version}</version>
+    </dependency>
+    </dependencies>
+
+    <properties>
+        <commons-collections4.version>4.3</commons-collections4.version>
+        <guava.version>27.1-jre</guava.version>
+    </properties>
+</project>

core-java-collections-set/src/test/java/com/baeldung/set/SetOperationsUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.set;
+
+import static org.junit.Assert.*;
+
+import org.apache.commons.collections4.SetUtils;
+import org.junit.Test;
+
+import com.google.common.collect.Sets;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class SetOperationsUnitTest {
+
+    private Set<Integer> setA = setOf(1,2,3,4);
+    private Set<Integer> setB = setOf(2,4,6,8);
+    
+    private static Set<Integer> setOf(Integer... values) {
+        return new HashSet<Integer>(Arrays.asList(values));
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeRetainAll_ThenWeIntersectThem() {
+        Set<Integer> intersectSet = new HashSet<>(setA);
+        intersectSet.retainAll(setB);
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeAddAll_ThenWeUnionThem() {
+        Set<Integer> unionSet = new HashSet<>(setA);
+        unionSet.addAll(setB);
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenRemoveAll_ThenWeGetTheDifference() {
+        Set<Integer> differenceSet = new HashSet<>(setA);
+        differenceSet.removeAll(setB);
+        assertEquals(setOf(1,3), differenceSet);
+    }
+    
+    @Test
+    public void givenTwoStreams_WhenWeFilterThem_ThenWeCanGetTheIntersect() {
+        Set<Integer> intersectSet = setA.stream()
+            .filter(setB::contains)
+            .collect(Collectors.toSet());
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoStreams_WhenWeConcatThem_ThenWeGetTheUnion() {
+        Set<Integer> unionSet = Stream.concat(setA.stream(), setB.stream())
+            .collect(Collectors.toSet());
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+    
+    @Test
+    public void givenTwoStreams_WhenWeFilterThem_ThenWeCanGetTheDifference() {
+        Set<Integer> differenceSet = setA.stream()
+            .filter(val -> !setB.contains(val))
+            .collect(Collectors.toSet());
+        assertEquals(setOf(1,3), differenceSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeUseApacheCommonsIntersect_ThenWeGetTheIntersect() {
+        Set<Integer> intersectSet = SetUtils.intersection(setA, setB);
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeUseApacheCommonsUnion_ThenWeGetTheUnion() {
+        Set<Integer> unionSet = SetUtils.union(setA, setB);
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+    
+    
+    @Test
+    public void givenTwoSets_WhenWeUseGuavaIntersect_ThenWeGetTheIntersect() {
+        Set<Integer> intersectSet = Sets.intersection(setA, setB);
+        assertEquals(setOf(2,4), intersectSet);
+    }
+    
+    @Test
+    public void givenTwoSets_WhenWeUseGuavaUnion_ThenWeGetTheUnion() {
+        Set<Integer> unionSet = Sets.union(setA, setB);
+        assertEquals(setOf(1,2,3,4,6,8), unionSet);
+    }
+}

pom.xml

@@ -389,6 +389,7 @@
                 <module>core-java-collections</module>
                 <module>core-java-collections-map</module>
                 <module>core-java-collections-list</module>
+                <module>core-java-collections-set</module>
                 <module>core-java-concurrency-basic</module>
                 <module>core-java-concurrency-collections</module>
                 <module>core-java-io</module>
@@ -1059,6 +1060,7 @@
                 <module>core-java-collections</module>
                 <module>core-java-collections-map</module>
                 <module>core-java-collections-list</module>
+                <module>core-java-collections-set</module>
                 <module>core-java-concurrency-basic</module>
                 <module>core-java-concurrency-collections</module>
                 <module>core-java-io</module>