// onjava/Sets.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
package onjava;
import java.util.*;

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