Set union and intersection : Set « Collections « Java Tutorial

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* Copyright 2001-2004 Laszlo Systems, Inc.  All Rights Reserved.              *
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import java.util.*;

 * A utility class containing set utility functions.
 * @author Oliver Steele
public abstract class SetUtils {
    public static boolean containsAny(Set a, Set b) {
        for (Iterator iter = b.iterator(); iter.hasNext(); ) {
            if (a.contains( {
                return true;
        return false;

    public static Set intersection(Set a, Set b) {
        Set c = new HashSet();
        for (Iterator iter = b.iterator(); iter.hasNext(); ) {
            Object e =;
            if (a.contains(e)) {
        return c;

9.18.1.Convert a List to a Set
9.18.2.Convert an ArrayList to HashSet
9.18.3.Creating a Sorted Set
9.18.4.Create new sets from Iterable, var argv
9.18.5.Create an array containing the elements in a set
9.18.6.Comparable with a sorted collection.
9.18.7.Duplicate elements are discarded
9.18.8.Creating a Set That Retains Order-of-Insertion
9.18.9.Convert Set into array
9.18.10.Convert Set into List
9.18.11.Copy all the elements from set2 to set1 (set1 += set2), set1 becomes the union of set1 and set2
9.18.12.Remove all the elements in set1 from set2 (set1 -= set2), set1 becomes the asymmetric difference of set1 and set2
9.18.13.Get the intersection of set1 and set2, set1 becomes the intersection of set1 and set2
9.18.14.Set operations: union, intersection, difference, symmetric difference, is subset, is superset
9.18.15.Remove all elements from a set
9.18.16.List Set
9.18.17.Set implementation that use == instead of equals()
9.18.18.Set union and intersection
9.18.19.Set with values iterated in insertion order.
9.18.20.Implements the Set interface, backed by a ConcurrentHashMap instance
9.18.21.A weak HashSet: element stored in the WeakHashSet might be garbage collected
9.18.22.An IdentitySet that uses reference-equality instead of object-equality
9.18.23.A thin wrapper around a List transforming it into a modifiable Set.
9.18.24.Concurrent set
9.18.25.Set that compares object by identity rather than equality