java/util/TreeSet.java

/*
 * %W% %E%
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;
import java.util.*; // for javadoc (till 6280605 is fixed)

/**
 * A {@link NavigableSet} implementation based on a {@link TreeMap}.
 * The elements are ordered using their {@linkplain Comparable natural
 * ordering}, or by a {@link Comparator} provided at set creation
 * time, depending on which constructor is used.
 *
 * <p>This implementation provides guaranteed log(n) time cost for the basic
 * operations (<tt>add</tt>, <tt>remove</tt> and <tt>contains</tt>).
 *
 * <p>Note that the ordering maintained by a set (whether or not an explicit
 * comparator is provided) must be <i>consistent with equals</i> if it is to
 * correctly implement the <tt>Set</tt> interface.  (See <tt>Comparable</tt>
 * or <tt>Comparator</tt> for a precise definition of <i>consistent with
 * equals</i>.)  This is so because the <tt>Set</tt> interface is defined in
 * terms of the <tt>equals</tt> operation, but a <tt>TreeSet</tt> instance
 * performs all element comparisons using its <tt>compareTo</tt> (or
 * <tt>compare</tt>) method, so two elements that are deemed equal by this method
 * are, from the standpoint of the set, equal.  The behavior of a set
 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it
 * just fails to obey the general contract of the <tt>Set</tt> interface.
 *
 * <p><b>Note that this implementation is not synchronized.</b> If multiple
 * threads access a set concurrently, and at least one of the threads modifies
 * the set, it <i>must</i> be synchronized externally.  This is typically
 * accomplished by synchronizing on some object that naturally encapsulates
 * the set.  If no such object exists, the set should be "wrapped" using the
 * <tt>Collections.synchronizedSet</tt> method.  This is best done at creation
 * time, to prevent accidental unsynchronized access to the set: <pre>
 *     SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
 * </pre>
 *
 * <p>The iterators returned by this class's <tt>iterator</tt> method are
 * <i>fail-fast</i>: if the set is modified at any time after the iterator is
 * created, in any way except through the iterator's own <tt>remove</tt>
 * method, the iterator will throw a {@link ConcurrentModificationException}.
 * Thus, in the face of concurrent modification, the iterator fails quickly
 * and cleanly, rather than risking arbitrary, non-deterministic behavior at
 * an undetermined time in the future.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:   <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 *
 * @author  Josh Bloch
 * @version %I%, %G%
 * @see     Collection
 * @see     Set
 * @see     HashSet
 * @see     Comparable
 * @see     Comparator
 * @see     Collections#synchronizedSortedSet(SortedSet)
 * @see     TreeMap
 * @since   1.2
 */

public class TreeSet<E>
    extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable
{
    private transient NavigableMap<E,Object> m; // The backing Map

    // Dummy value to associate with an Object in the backing Map
    private static final Object PRESENT = new Object();

    /**
     * Constructs a set backed by the specified navigable map.
     */
    private TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }

    /**
     * Constructs a new, empty tree set, sorted according to the
     * natural ordering of its elements.  All elements inserted into
     * the set must implement the {@link Comparable} interface.
     * Furthermore, all such elements must be <i>mutually
     * comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
     * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
     * <tt>e2</tt> in the set.  If the user attempts to add an element
     * to the set that violates this constraint (for example, the user
     * attempts to add a string element to a set whose elements are
     * integers), the <tt>add(Object)</tt> call will throw a
     * <tt>ClassCastException</tt>.
     */
    public TreeSet() {
        this(new TreeMap<E,Object>());
    }

    /**
     * Constructs a new, empty tree set, sorted according to the specified
     * comparator.  All elements inserted into the set must be <i>mutually
     * comparable</i> by the specified comparator: <tt>comparator.compare(e1,
     * e2)</tt> must not throw a <tt>ClassCastException</tt> for any elements
     * <tt>e1</tt> and <tt>e2</tt> in the set.  If the user attempts to add
     * an element to the set that violates this constraint, the
     * <tt>add(Object)</tt> call will throw a <tt>ClassCastException</tt>.
     *
     * @param comparator the comparator that will be used to order this set.
     *        If <tt>null</tt>, the {@linkplain Comparable natural
     *        ordering} of the elements will be used.
     */
    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<E,Object>(comparator));
    }

    /**
     * Constructs a new tree set containing the elements in the specified
     * collection, sorted according to the <i>natural ordering</i> of its
     * elements.  All elements inserted into the set must implement the
     * {@link Comparable} interface.  Furthermore, all such elements must be
     * <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
     * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
     * <tt>e2</tt> in the set.
     *
     * @param c collection whose elements will comprise the new set
     * @throws ClassCastException if the elements in <tt>c</tt> are
     *         not {@link Comparable}, or are not mutually comparable
     * @throws NullPointerException if the specified collection is null
     */
    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }

    /**
     * Constructs a new tree set containing the same elements and
     * using the same ordering as the specified sorted set.
     *
     * @param s sorted set whose elements will comprise the new set
     * @throws NullPointerException if the specified sorted set is null
     */
    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }

    /**
     * Returns an iterator over the elements in this set in ascending order.
     *
     * @return an iterator over the elements in this set in ascending order
     */
    public Iterator<E> iterator() {
        return m.keySet().iterator();
    }

    /**
     * Returns an iterator over the elements in this set in descending order.
     *
     * @return an iterator over the elements in this set in descending order
     */
    public Iterator<E> descendingIterator() {
        return m.descendingKeySet().iterator();
    }

    /**
     * Returns the number of elements in this set (its cardinality).
     *
     * @return the number of elements in this set (its cardinality)
     */
    public int size() {
        return m.size();
    }

    /**
     * Returns <tt>true</tt> if this set contains no elements.
     *
     * @return <tt>true</tt> if this set contains no elements
     */
    public boolean isEmpty() {
        return m.isEmpty();
    }

    /**
     * Returns <tt>true</tt> if this set contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this set
     * contains an element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o object to be checked for containment in this set
     * @return <tt>true</tt> if this set contains the specified element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean contains(Object o) {
        return m.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     * More formally, adds the specified element <tt>e</tt> to this set if
     * the set contains no element <tt>e2</tt> such that
     * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns <tt>false</tt>.
     *
     * @param e element to be added to this set
     * @return <tt>true</tt> if this set did not already contain the specified
     *         element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }

    /**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
     * if this set contains such an element.  Returns <tt>true</tt> if
     * this set contained the element (or equivalently, if this set
     * changed as a result of the call).  (This set will not contain the
     * element once the call returns.)
     *
     * @param o object to be removed from this set, if present
     * @return <tt>true</tt> if this set contained the specified element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean remove(Object o) {
        return m.remove(o)==PRESENT;
    }

    /**
     * Removes all of the elements from this set.
     * The set will be empty after this call returns.
     */
    public void clear() {
        m.clear();
    }

    /**
     * Adds all of the elements in the specified collection to this set.
     *
     * @param c collection containing elements to be added to this set
     * @return <tt>true</tt> if this set changed as a result of the call
     * @throws ClassCastException if the elements provided cannot be compared
     *         with the elements currently in the set
     * @throws NullPointerException if the specified collection is null or
     *         if any element is null and this set uses natural ordering, or
     *         its comparator does not permit null elements
     */
    public  boolean addAll(Collection<? extends E> c) {
        // Use linear-time version if applicable
        if (m.size()==0 && c.size() > 0 &&
            c instanceof SortedSet &&
            m instanceof TreeMap) {
            SortedSet<? extends E> set = (SortedSet<? extends E>) c;
            TreeMap<E,Object> map = (TreeMap<E, Object>) m;
            Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
            Comparator<? super E> mc = map.comparator();
            if (cc==mc || (cc != null && cc.equals(mc))) {
                map.addAllForTreeSet(set, PRESENT);
                return true;
            }
        }
        return super.addAll(c);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> or
     *         <tt>toElement</tt> is null and this set uses natural ordering,
     *         or its comparator does not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
        return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>toElement</tt> is null and
     *         this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> navigableHeadSet(E toElement) {
        return new TreeSet<E>(m.navigableHeadMap(toElement));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> is null and
     *         this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public NavigableSet<E> navigableTailSet(E fromElement) {
        return new TreeSet<E>(m.navigableTailMap(fromElement));
    }

    /**
     * Equivalent to {@link #navigableSubSet} but with a return type
     * conforming to the <tt>SortedSet</tt> interface.
     *
     * <p>{@inheritDoc}
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> or
     *         <tt>toElement</tt> is null and this set uses natural ordering,
     *         or its comparator does not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> subSet(E fromElement, E toElement) {
        return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
    }

    /**
     * Equivalent to {@link #navigableHeadSet} but with a return type
     * conforming to the <tt>SortedSet</tt> interface.
     *
     * <p>{@inheritDoc}
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>toElement</tt> is null
     *         and this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> headSet(E toElement) {
        return new TreeSet<E>(m.navigableHeadMap(toElement));
    }

    /**
     * Equivalent to {@link #navigableTailSet} but with a return type
     * conforming to the <tt>SortedSet</tt> interface.
     *
     * <p>{@inheritDoc}
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> is null
     *         and this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> tailSet(E fromElement) {
        return new TreeSet<E>(m.navigableTailMap(fromElement));
    }

    public Comparator<? super E> comparator() {
        return m.comparator();
    }

    /**
     * @throws NoSuchElementException {@inheritDoc}
     */
    public E first() {
        return m.firstKey();
    }

    /**
     * @throws NoSuchElementException {@inheritDoc}
     */
    public E last() {
        return m.lastKey();
    }

    // NavigableSet API methods

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public E lower(E e) {
        return m.lowerKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public E floor(E e) {
        return m.floorKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public E ceiling(E e) {
        return m.ceilingKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public E higher(E e) {
        return m.higherKey(e);
    }

    public E pollFirst() {
        Map.Entry<E,?> e = m.pollFirstEntry();
        return (e == null)? null : e.getKey();
    }

    public E pollLast() {
        Map.Entry<E,?> e = m.pollLastEntry();
        return (e == null)? null : e.getKey();
    }

    /**
     * Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
     * themselves are not cloned.)
     *
     * @return a shallow copy of this set
     */
    public Object clone() {
        TreeSet<E> clone = null;
        try {
            clone = (TreeSet<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }

        clone.m = new TreeMap<E,Object>(m);

        return clone;
    }

    /**
     * Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
     * serialize it).
     *
     * @serialData Emits the comparator used to order this set, or
     *             <tt>null</tt> if it obeys its elements' natural ordering
     *             (Object), followed by the size of the set (the number of
     *             elements it contains) (int), followed by all of its
     *             elements (each an Object) in order (as determined by the
     *             set's Comparator, or by the elements' natural ordering if
     *             the set has no Comparator).
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        // Write out any hidden stuff
        s.defaultWriteObject();

        // Write out Comparator
        s.writeObject(m.comparator());

        // Write out size
        s.writeInt(m.size());

        // Write out all elements in the proper order.
        for (Iterator i=m.keySet().iterator(); i.hasNext(); )
            s.writeObject(i.next());
    }

    /**
     * Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
     * deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in any hidden stuff
        s.defaultReadObject();

        // Read in Comparator
        Comparator<? super E> c = (Comparator<? super E>) s.readObject();

        // Create backing TreeMap
        TreeMap<E,Object> tm;
        if (c==null)
            tm = new TreeMap<E,Object>();
        else
            tm = new TreeMap<E,Object>(c);
        m = tm;

        // Read in size
        int size = s.readInt();

        tm.readTreeSet(size, s, PRESENT);
    }

    private static final long serialVersionUID = -2479143000061671589L;
}
Revision:	1.16
Committed:	Sun Jun 19 23:01:12 2005 UTC (18 years, 11 months ago) by jsr166
Branch:	MAIN
Changes since 1.15:	+20 -5 lines
Log Message:	doc fixes
#	Content
1	/*
2	* %W% %E%
3	*
4	* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	*/
7
8	package java.util;
9	import java.util.*; // for javadoc (till 6280605 is fixed)
10
11	/**
12	* A {@link NavigableSet} implementation based on a {@link TreeMap}.
13	* The elements are ordered using their {@linkplain Comparable natural
14	* ordering}, or by a {@link Comparator} provided at set creation
15	* time, depending on which constructor is used.
16	*
17	* <p>This implementation provides guaranteed log(n) time cost for the basic
18	* operations (<tt>add</tt>, <tt>remove</tt> and <tt>contains</tt>).
19	*
20	* <p>Note that the ordering maintained by a set (whether or not an explicit
21	* comparator is provided) must be <i>consistent with equals</i> if it is to
22	* correctly implement the <tt>Set</tt> interface. (See <tt>Comparable</tt>
23	* or <tt>Comparator</tt> for a precise definition of <i>consistent with
24	* equals</i>.) This is so because the <tt>Set</tt> interface is defined in
25	* terms of the <tt>equals</tt> operation, but a <tt>TreeSet</tt> instance
26	* performs all element comparisons using its <tt>compareTo</tt> (or
27	* <tt>compare</tt>) method, so two elements that are deemed equal by this method
28	* are, from the standpoint of the set, equal. The behavior of a set
29	* <i>is</i> well-defined even if its ordering is inconsistent with equals; it
30	* just fails to obey the general contract of the <tt>Set</tt> interface.
31	*
32	* <p><b>Note that this implementation is not synchronized.</b> If multiple
33	* threads access a set concurrently, and at least one of the threads modifies
34	* the set, it <i>must</i> be synchronized externally. This is typically
35	* accomplished by synchronizing on some object that naturally encapsulates
36	* the set. If no such object exists, the set should be "wrapped" using the
37	* <tt>Collections.synchronizedSet</tt> method. This is best done at creation
38	* time, to prevent accidental unsynchronized access to the set: <pre>
39	* SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
40	* </pre>
41	*
42	* <p>The iterators returned by this class's <tt>iterator</tt> method are
43	* <i>fail-fast</i>: if the set is modified at any time after the iterator is
44	* created, in any way except through the iterator's own <tt>remove</tt>
45	* method, the iterator will throw a {@link ConcurrentModificationException}.
46	* Thus, in the face of concurrent modification, the iterator fails quickly
47	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
48	* an undetermined time in the future.
49	*
50	* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
51	* as it is, generally speaking, impossible to make any hard guarantees in the
52	* presence of unsynchronized concurrent modification. Fail-fast iterators
53	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
54	* Therefore, it would be wrong to write a program that depended on this
55	* exception for its correctness: <i>the fail-fast behavior of iterators
56	* should be used only to detect bugs.</i>
57	*
58	* <p>This class is a member of the
59	* <a href="{@docRoot}/../guide/collections/index.html">
60	* Java Collections Framework</a>.
61	*
62	* @param <E> the type of elements maintained by this set
63	*
64	* @author Josh Bloch
65	* @version %I%, %G%
66	* @see Collection
67	* @see Set
68	* @see HashSet
69	* @see Comparable
70	* @see Comparator
71	* @see Collections#synchronizedSortedSet(SortedSet)
72	* @see TreeMap
73	* @since 1.2
74	*/
75
76	public class TreeSet<E>
77	extends AbstractSet<E>
78	implements NavigableSet<E>, Cloneable, java.io.Serializable
79	{
80	private transient NavigableMap<E,Object> m; // The backing Map
81
82	// Dummy value to associate with an Object in the backing Map
83	private static final Object PRESENT = new Object();
84
85	/**
86	* Constructs a set backed by the specified navigable map.
87	*/
88	private TreeSet(NavigableMap<E,Object> m) {
89	this.m = m;
90	}
91
92	/**
93	* Constructs a new, empty tree set, sorted according to the
94	* natural ordering of its elements. All elements inserted into
95	* the set must implement the {@link Comparable} interface.
96	* Furthermore, all such elements must be <i>mutually
97	* comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
98	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
99	* <tt>e2</tt> in the set. If the user attempts to add an element
100	* to the set that violates this constraint (for example, the user
101	* attempts to add a string element to a set whose elements are
102	* integers), the <tt>add(Object)</tt> call will throw a
103	* <tt>ClassCastException</tt>.
104	*/
105	public TreeSet() {
106	this(new TreeMap<E,Object>());
107	}
108
109	/**
110	* Constructs a new, empty tree set, sorted according to the specified
111	* comparator. All elements inserted into the set must be <i>mutually
112	* comparable</i> by the specified comparator: <tt>comparator.compare(e1,
113	* e2)</tt> must not throw a <tt>ClassCastException</tt> for any elements
114	* <tt>e1</tt> and <tt>e2</tt> in the set. If the user attempts to add
115	* an element to the set that violates this constraint, the
116	* <tt>add(Object)</tt> call will throw a <tt>ClassCastException</tt>.
117	*
118	* @param comparator the comparator that will be used to order this set.
119	* If <tt>null</tt>, the {@linkplain Comparable natural
120	* ordering} of the elements will be used.
121	*/
122	public TreeSet(Comparator<? super E> comparator) {
123	this(new TreeMap<E,Object>(comparator));
124	}
125
126	/**
127	* Constructs a new tree set containing the elements in the specified
128	* collection, sorted according to the <i>natural ordering</i> of its
129	* elements. All elements inserted into the set must implement the
130	* {@link Comparable} interface. Furthermore, all such elements must be
131	* <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
132	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
133	* <tt>e2</tt> in the set.
134	*
135	* @param c collection whose elements will comprise the new set
136	* @throws ClassCastException if the elements in <tt>c</tt> are
137	* not {@link Comparable}, or are not mutually comparable
138	* @throws NullPointerException if the specified collection is null
139	*/
140	public TreeSet(Collection<? extends E> c) {
141	this();
142	addAll(c);
143	}
144
145	/**
146	* Constructs a new tree set containing the same elements and
147	* using the same ordering as the specified sorted set.
148	*
149	* @param s sorted set whose elements will comprise the new set
150	* @throws NullPointerException if the specified sorted set is null
151	*/
152	public TreeSet(SortedSet<E> s) {
153	this(s.comparator());
154	addAll(s);
155	}
156
157	/**
158	* Returns an iterator over the elements in this set in ascending order.
159	*
160	* @return an iterator over the elements in this set in ascending order
161	*/
162	public Iterator<E> iterator() {
163	return m.keySet().iterator();
164	}
165
166	/**
167	* Returns an iterator over the elements in this set in descending order.
168	*
169	* @return an iterator over the elements in this set in descending order
170	*/
171	public Iterator<E> descendingIterator() {
172	return m.descendingKeySet().iterator();
173	}
174
175	/**
176	* Returns the number of elements in this set (its cardinality).
177	*
178	* @return the number of elements in this set (its cardinality)
179	*/
180	public int size() {
181	return m.size();
182	}
183
184	/**
185	* Returns <tt>true</tt> if this set contains no elements.
186	*
187	* @return <tt>true</tt> if this set contains no elements
188	*/
189	public boolean isEmpty() {
190	return m.isEmpty();
191	}
192
193	/**
194	* Returns <tt>true</tt> if this set contains the specified element.
195	* More formally, returns <tt>true</tt> if and only if this set
196	* contains an element <tt>e</tt> such that
197	* <tt>(o==null ? e==null : o.equals(e))</tt>.
198	*
199	* @param o object to be checked for containment in this set
200	* @return <tt>true</tt> if this set contains the specified element
201	* @throws ClassCastException if the specified object cannot be compared
202	* with the elements currently in the set
203	* @throws NullPointerException if the specified element is null
204	* and this set uses natural ordering, or its comparator
205	* does not permit null elements
206	*/
207	public boolean contains(Object o) {
208	return m.containsKey(o);
209	}
210
211	/**
212	* Adds the specified element to this set if it is not already present.
213	* More formally, adds the specified element <tt>e</tt> to this set if
214	* the set contains no element <tt>e2</tt> such that
215	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
216	* If this set already contains the element, the call leaves the set
217	* unchanged and returns <tt>false</tt>.
218	*
219	* @param e element to be added to this set
220	* @return <tt>true</tt> if this set did not already contain the specified
221	* element
222	* @throws ClassCastException if the specified object cannot be compared
223	* with the elements currently in this set
224	* @throws NullPointerException if the specified element is null
225	* and this set uses natural ordering, or its comparator
226	* does not permit null elements
227	*/
228	public boolean add(E e) {
229	return m.put(e, PRESENT)==null;
230	}
231
232	/**
233	* Removes the specified element from this set if it is present.
234	* More formally, removes an element <tt>e</tt> such that
235	* <tt>(o==null ? e==null : o.equals(e))</tt>,
236	* if this set contains such an element. Returns <tt>true</tt> if
237	* this set contained the element (or equivalently, if this set
238	* changed as a result of the call). (This set will not contain the
239	* element once the call returns.)
240	*
241	* @param o object to be removed from this set, if present
242	* @return <tt>true</tt> if this set contained the specified element
243	* @throws ClassCastException if the specified object cannot be compared
244	* with the elements currently in this set
245	* @throws NullPointerException if the specified element is null
246	* and this set uses natural ordering, or its comparator
247	* does not permit null elements
248	*/
249	public boolean remove(Object o) {
250	return m.remove(o)==PRESENT;
251	}
252
253	/**
254	* Removes all of the elements from this set.
255	* The set will be empty after this call returns.
256	*/
257	public void clear() {
258	m.clear();
259	}
260
261	/**
262	* Adds all of the elements in the specified collection to this set.
263	*
264	* @param c collection containing elements to be added to this set
265	* @return <tt>true</tt> if this set changed as a result of the call
266	* @throws ClassCastException if the elements provided cannot be compared
267	* with the elements currently in the set
268	* @throws NullPointerException if the specified collection is null or
269	* if any element is null and this set uses natural ordering, or
270	* its comparator does not permit null elements
271	*/
272	public boolean addAll(Collection<? extends E> c) {
273	// Use linear-time version if applicable
274	if (m.size()==0 && c.size() > 0 &&
275	c instanceof SortedSet &&
276	m instanceof TreeMap) {
277	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
278	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
279	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
280	Comparator<? super E> mc = map.comparator();
281	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
282	map.addAllForTreeSet(set, PRESENT);
283	return true;
284	}
285	}
286	return super.addAll(c);
287	}
288
289	/**
290	* @throws ClassCastException {@inheritDoc}
291	* @throws NullPointerException if <tt>fromElement</tt> or
292	* <tt>toElement</tt> is null and this set uses natural ordering,
293	* or its comparator does not permit null elements
294	* @throws IllegalArgumentException {@inheritDoc}
295	*/
296	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
297	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
298	}
299
300	/**
301	* @throws ClassCastException {@inheritDoc}
302	* @throws NullPointerException if <tt>toElement</tt> is null and
303	* this set uses natural ordering, or its comparator does
304	* not permit null elements
305	* @throws IllegalArgumentException {@inheritDoc}
306	*/
307	public NavigableSet<E> navigableHeadSet(E toElement) {
308	return new TreeSet<E>(m.navigableHeadMap(toElement));
309	}
310
311	/**
312	* @throws ClassCastException {@inheritDoc}
313	* @throws NullPointerException if <tt>fromElement</tt> is null and
314	* this set uses natural ordering, or its comparator does
315	* not permit null elements
316	* @throws IllegalArgumentException {@inheritDoc}
317	*/
318	public NavigableSet<E> navigableTailSet(E fromElement) {
319	return new TreeSet<E>(m.navigableTailMap(fromElement));
320	}
321
322	/**
323	* Equivalent to {@link #navigableSubSet} but with a return type
324	* conforming to the <tt>SortedSet</tt> interface.
325	*
326	* <p>{@inheritDoc}
327	*
328	* @throws ClassCastException {@inheritDoc}
329	* @throws NullPointerException if <tt>fromElement</tt> or
330	* <tt>toElement</tt> is null and this set uses natural ordering,
331	* or its comparator does not permit null elements
332	* @throws IllegalArgumentException {@inheritDoc}
333	*/
334	public SortedSet<E> subSet(E fromElement, E toElement) {
335	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
336	}
337
338	/**
339	* Equivalent to {@link #navigableHeadSet} but with a return type
340	* conforming to the <tt>SortedSet</tt> interface.
341	*
342	* <p>{@inheritDoc}
343	*
344	* @throws ClassCastException {@inheritDoc}
345	* @throws NullPointerException if <tt>toElement</tt> is null
346	* and this set uses natural ordering, or its comparator does
347	* not permit null elements
348	* @throws IllegalArgumentException {@inheritDoc}
349	*/
350	public SortedSet<E> headSet(E toElement) {
351	return new TreeSet<E>(m.navigableHeadMap(toElement));
352	}
353
354	/**
355	* Equivalent to {@link #navigableTailSet} but with a return type
356	* conforming to the <tt>SortedSet</tt> interface.
357	*
358	* <p>{@inheritDoc}
359	*
360	* @throws ClassCastException {@inheritDoc}
361	* @throws NullPointerException if <tt>fromElement</tt> is null
362	* and this set uses natural ordering, or its comparator does
363	* not permit null elements
364	* @throws IllegalArgumentException {@inheritDoc}
365	*/
366	public SortedSet<E> tailSet(E fromElement) {
367	return new TreeSet<E>(m.navigableTailMap(fromElement));
368	}
369
370	public Comparator<? super E> comparator() {
371	return m.comparator();
372	}
373
374	/**
375	* @throws NoSuchElementException {@inheritDoc}
376	*/
377	public E first() {
378	return m.firstKey();
379	}
380
381	/**
382	* @throws NoSuchElementException {@inheritDoc}
383	*/
384	public E last() {
385	return m.lastKey();
386	}
387
388	// NavigableSet API methods
389
390	/**
391	* @throws ClassCastException {@inheritDoc}
392	* @throws NullPointerException if the specified element is null
393	* and this set uses natural ordering, or its comparator
394	* does not permit null elements
395	*/
396	public E lower(E e) {
397	return m.lowerKey(e);
398	}
399
400	/**
401	* @throws ClassCastException {@inheritDoc}
402	* @throws NullPointerException if the specified element is null
403	* and this set uses natural ordering, or its comparator
404	* does not permit null elements
405	*/
406	public E floor(E e) {
407	return m.floorKey(e);
408	}
409
410	/**
411	* @throws ClassCastException {@inheritDoc}
412	* @throws NullPointerException if the specified element is null
413	* and this set uses natural ordering, or its comparator
414	* does not permit null elements
415	*/
416	public E ceiling(E e) {
417	return m.ceilingKey(e);
418	}
419
420	/**
421	* @throws ClassCastException {@inheritDoc}
422	* @throws NullPointerException if the specified element is null
423	* and this set uses natural ordering, or its comparator
424	* does not permit null elements
425	*/
426	public E higher(E e) {
427	return m.higherKey(e);
428	}
429
430	public E pollFirst() {
431	Map.Entry<E,?> e = m.pollFirstEntry();
432	return (e == null)? null : e.getKey();
433	}
434
435	public E pollLast() {
436	Map.Entry<E,?> e = m.pollLastEntry();
437	return (e == null)? null : e.getKey();
438	}
439
440	/**
441	* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
442	* themselves are not cloned.)
443	*
444	* @return a shallow copy of this set
445	*/
446	public Object clone() {
447	TreeSet<E> clone = null;
448	try {
449	clone = (TreeSet<E>) super.clone();
450	} catch (CloneNotSupportedException e) {
451	throw new InternalError();
452	}
453
454	clone.m = new TreeMap<E,Object>(m);
455
456	return clone;
457	}
458
459	/**
460	* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
461	* serialize it).
462	*
463	* @serialData Emits the comparator used to order this set, or
464	* <tt>null</tt> if it obeys its elements' natural ordering
465	* (Object), followed by the size of the set (the number of
466	* elements it contains) (int), followed by all of its
467	* elements (each an Object) in order (as determined by the
468	* set's Comparator, or by the elements' natural ordering if
469	* the set has no Comparator).
470	*/
471	private void writeObject(java.io.ObjectOutputStream s)
472	throws java.io.IOException {
473	// Write out any hidden stuff
474	s.defaultWriteObject();
475
476	// Write out Comparator
477	s.writeObject(m.comparator());
478
479	// Write out size
480	s.writeInt(m.size());
481
482	// Write out all elements in the proper order.
483	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
484	s.writeObject(i.next());
485	}
486
487	/**
488	* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
489	* deserialize it).
490	*/
491	private void readObject(java.io.ObjectInputStream s)
492	throws java.io.IOException, ClassNotFoundException {
493	// Read in any hidden stuff
494	s.defaultReadObject();
495
496	// Read in Comparator
497	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
498
499	// Create backing TreeMap
500	TreeMap<E,Object> tm;
501	if (c==null)
502	tm = new TreeMap<E,Object>();
503	else
504	tm = new TreeMap<E,Object>(c);
505	m = tm;
506
507	// Read in size
508	int size = s.readInt();
509
510	tm.readTreeSet(size, s, PRESENT);
511	}
512
513	private static final long serialVersionUID = -2479143000061671589L;
514	}