Collections - Beginning Java 8 Language Features - page 530

Listing 12-7 demonstrates how to use the Set interface to perform mathematical set operations.
Listing 12-7. Performing Mathematical Set Operations Using the Set Interface
// SetOperations.java
package com.jdojo.collections;
import java.util.HashSet;
import java.util.Set;
public class SetOperations {
public static void main(String[] args) {
// Create a set
Set<String> s1 = new HashSet<>();
s1.add("John");
s1.add("Donna");
s1.add("Ken");
// Create another set
Set<String> s2 = new HashSet<>();
s2.add("Ellen");
s2.add("Sara");
s2.add("Donna");
//Print the elements of both sets
System.out.println("s1: " + s1);
System.out.println("s2: " + s2);
// Perform set operations
performUnion(s1, s2);
performIntersection(s1, s2);
performDifference(s1, s2);
testForSubset(s1, s2);
}
public static void performUnion(Set<String> s1, Set<String> s2) {
Set<String> s1Unions2 = new HashSet<>(s1);
s1Unions2.addAll(s2);
System.out.println("s1 union s2: " + s1Unions2);
}
public static void performIntersection(Set<String> s1, Set<String> s2) {
Set<String> s1Intersections2 = new HashSet<>(s1);
s1Intersections2.retainAll(s2);
System.out.println("s1 intersection s2: " + s1Intersections2);
}
public static void performDifference(Set<String> s1, Set<String> s2) {
Set<String> s1Differences2 = new HashSet<>(s1);
s1Differences2.removeAll(s2);