Class HashSet

lib/java/util/HashSet.java:26–214

HashSet is an implementation of a Set. All optional operations (adding and removing) are supported. The elements can be any objects.

 * removing) are supported. The elements can be any objects.
 */
public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable,
        Serializable {

    private static final long serialVersionUID = -5024744406713321676L;

    transient HashMap<E, HashSet<E>> backingMap;

    /**
     * Constructs a new empty instance of {@code HashSet}.
     */
    public HashSet() {
        this(new HashMap<E, HashSet<E>>());
    }

    /**
     * Constructs a new instance of {@code HashSet} with the specified capacity.
     * 
     * @param capacity
     *            the initial capacity of this {@code HashSet}.
     */
    public HashSet(int capacity) {
        this(new HashMap<E, HashSet<E>>(capacity));
    }

    /**
     * Constructs a new instance of {@code HashSet} with the specified capacity
     * and load factor.
     * 
     * @param capacity
     *            the initial capacity.
     * @param loadFactor
     *            the initial load factor.
     */
    public HashSet(int capacity, float loadFactor) {
        this(new HashMap<E, HashSet<E>>(capacity, loadFactor));
    }

    /**
     * Constructs a new instance of {@code HashSet} containing the unique
     * elements in the specified collection.
     * 
     * @param collection
     *            the collection of elements to add.
     */
    public HashSet(Collection<? extends E> collection) {
        this(new HashMap<E, HashSet<E>>(collection.size() < 6 ? 11 : collection
                .size() * 2));
        for (E e : collection) {
            add(e);
        }
    }

    HashSet(HashMap<E, HashSet<E>> backingMap) {
        this.backingMap = backingMap;
    }

    /**
     * Adds the specified object to this {@code HashSet} if not already present.