OnJava8-Examples/onjava/Sets.java

// onjava/Sets.java
package onjava;
import java.util.*;

public class Sets {
  public static <T> Set<T> union(Set<T> a, Set<T> b) {
    Set<T> result = new HashSet<>(a);
    result.addAll(b);
    return result;
  }
  public static <T>
  Set<T> intersection(Set<T> a, Set<T> b) {
    Set<T> result = new HashSet<>(a);
    result.retainAll(b);
    return result;
  }
  // Subtract subset from superset:
  public static <T> Set<T>
  difference(Set<T> superset, Set<T> subset) {
    Set<T> result = new HashSet<>(superset);
    result.removeAll(subset);
    return result;
  }
  // Reflexive--everything not in the intersection:
  public static <T> Set<T> complement(Set<T> a, Set<T> b) {
    return difference(union(a, b), intersection(a, b));
  }
}