java/util/TreeSet.java

/*
 * %W% %E%
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;

/**
 * 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><strong>Note that this implementation is not synchronized.</strong>
 * If multiple threads access a tree 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
 * {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
 * 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     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
     * @since 1.6
     */
    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}
     * @since 1.6
     */
    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}
     * @since 1.6
     */
    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}
     * @since 1.6
     */
    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
     * @since 1.6
     */
    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
     * @since 1.6
     */
    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
     * @since 1.6
     */
    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
     * @since 1.6
     */
    public E higher(E e) {
        return m.higherKey(e);
    }

    /**
     * @since 1.6
     */
    public E pollFirst() {
        Map.Entry<E,?> e = m.pollFirstEntry();
        return (e == null)? null : e.getKey();
    }

    /**
     * @since 1.6
     */
    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:	1.20
Committed:	Tue Feb 7 20:54:24 2006 UTC (18 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.19:	+0 -1 lines
Log Message:	6378729: Remove workaround for 6280605
#	Content
1	/*
2	* %W% %E%
3	*
4	* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	*/
7
8	package java.util;
9
10	/**
11	* A {@link NavigableSet} implementation based on a {@link TreeMap}.
12	* The elements are ordered using their {@linkplain Comparable natural
13	* ordering}, or by a {@link Comparator} provided at set creation
14	* time, depending on which constructor is used.
15	*
16	* <p>This implementation provides guaranteed log(n) time cost for the basic
17	* operations (<tt>add</tt>, <tt>remove</tt> and <tt>contains</tt>).
18	*
19	* <p>Note that the ordering maintained by a set (whether or not an explicit
20	* comparator is provided) must be <i>consistent with equals</i> if it is to
21	* correctly implement the <tt>Set</tt> interface. (See <tt>Comparable</tt>
22	* or <tt>Comparator</tt> for a precise definition of <i>consistent with
23	* equals</i>.) This is so because the <tt>Set</tt> interface is defined in
24	* terms of the <tt>equals</tt> operation, but a <tt>TreeSet</tt> instance
25	* performs all element comparisons using its <tt>compareTo</tt> (or
26	* <tt>compare</tt>) method, so two elements that are deemed equal by this method
27	* are, from the standpoint of the set, equal. The behavior of a set
28	* <i>is</i> well-defined even if its ordering is inconsistent with equals; it
29	* just fails to obey the general contract of the <tt>Set</tt> interface.
30	*
31	* <p><strong>Note that this implementation is not synchronized.</strong>
32	* If multiple threads access a tree set concurrently, and at least one
33	* of the threads modifies the set, it <i>must</i> be synchronized
34	* externally. This is typically accomplished by synchronizing on some
35	* object that naturally encapsulates the set.
36	* If no such object exists, the set should be "wrapped" using the
37	* {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
38	* method. This is best done at creation time, to prevent accidental
39	* unsynchronized access to the set: <pre>
40	* SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</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 TreeMap
72	* @since 1.2
73	*/
74
75	public class TreeSet<E>
76	extends AbstractSet<E>
77	implements NavigableSet<E>, Cloneable, java.io.Serializable
78	{
79	private transient NavigableMap<E,Object> m; // The backing Map
80
81	// Dummy value to associate with an Object in the backing Map
82	private static final Object PRESENT = new Object();
83
84	/**
85	* Constructs a set backed by the specified navigable map.
86	*/
87	private TreeSet(NavigableMap<E,Object> m) {
88	this.m = m;
89	}
90
91	/**
92	* Constructs a new, empty tree set, sorted according to the
93	* natural ordering of its elements. All elements inserted into
94	* the set must implement the {@link Comparable} interface.
95	* Furthermore, all such elements must be <i>mutually
96	* comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
97	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
98	* <tt>e2</tt> in the set. If the user attempts to add an element
99	* to the set that violates this constraint (for example, the user
100	* attempts to add a string element to a set whose elements are
101	* integers), the <tt>add(Object)</tt> call will throw a
102	* <tt>ClassCastException</tt>.
103	*/
104	public TreeSet() {
105	this(new TreeMap<E,Object>());
106	}
107
108	/**
109	* Constructs a new, empty tree set, sorted according to the specified
110	* comparator. All elements inserted into the set must be <i>mutually
111	* comparable</i> by the specified comparator: <tt>comparator.compare(e1,
112	* e2)</tt> must not throw a <tt>ClassCastException</tt> for any elements
113	* <tt>e1</tt> and <tt>e2</tt> in the set. If the user attempts to add
114	* an element to the set that violates this constraint, the
115	* <tt>add(Object)</tt> call will throw a <tt>ClassCastException</tt>.
116	*
117	* @param comparator the comparator that will be used to order this set.
118	* If <tt>null</tt>, the {@linkplain Comparable natural
119	* ordering} of the elements will be used.
120	*/
121	public TreeSet(Comparator<? super E> comparator) {
122	this(new TreeMap<E,Object>(comparator));
123	}
124
125	/**
126	* Constructs a new tree set containing the elements in the specified
127	* collection, sorted according to the <i>natural ordering</i> of its
128	* elements. All elements inserted into the set must implement the
129	* {@link Comparable} interface. Furthermore, all such elements must be
130	* <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
131	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
132	* <tt>e2</tt> in the set.
133	*
134	* @param c collection whose elements will comprise the new set
135	* @throws ClassCastException if the elements in <tt>c</tt> are
136	* not {@link Comparable}, or are not mutually comparable
137	* @throws NullPointerException if the specified collection is null
138	*/
139	public TreeSet(Collection<? extends E> c) {
140	this();
141	addAll(c);
142	}
143
144	/**
145	* Constructs a new tree set containing the same elements and
146	* using the same ordering as the specified sorted set.
147	*
148	* @param s sorted set whose elements will comprise the new set
149	* @throws NullPointerException if the specified sorted set is null
150	*/
151	public TreeSet(SortedSet<E> s) {
152	this(s.comparator());
153	addAll(s);
154	}
155
156	/**
157	* Returns an iterator over the elements in this set in ascending order.
158	*
159	* @return an iterator over the elements in this set in ascending order
160	*/
161	public Iterator<E> iterator() {
162	return m.keySet().iterator();
163	}
164
165	/**
166	* Returns an iterator over the elements in this set in descending order.
167	*
168	* @return an iterator over the elements in this set in descending order
169	* @since 1.6
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	* @since 1.6
296	*/
297	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
298	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
299	}
300
301	/**
302	* @throws ClassCastException {@inheritDoc}
303	* @throws NullPointerException if <tt>toElement</tt> is null and
304	* this set uses natural ordering, or its comparator does
305	* not permit null elements
306	* @throws IllegalArgumentException {@inheritDoc}
307	* @since 1.6
308	*/
309	public NavigableSet<E> navigableHeadSet(E toElement) {
310	return new TreeSet<E>(m.navigableHeadMap(toElement));
311	}
312
313	/**
314	* @throws ClassCastException {@inheritDoc}
315	* @throws NullPointerException if <tt>fromElement</tt> is null and
316	* this set uses natural ordering, or its comparator does
317	* not permit null elements
318	* @throws IllegalArgumentException {@inheritDoc}
319	* @since 1.6
320	*/
321	public NavigableSet<E> navigableTailSet(E fromElement) {
322	return new TreeSet<E>(m.navigableTailMap(fromElement));
323	}
324
325	/**
326	* Equivalent to {@link #navigableSubSet} but with a return type
327	* conforming to the <tt>SortedSet</tt> interface.
328	*
329	* <p>{@inheritDoc}
330	*
331	* @throws ClassCastException {@inheritDoc}
332	* @throws NullPointerException if <tt>fromElement</tt> or
333	* <tt>toElement</tt> is null and this set uses natural ordering,
334	* or its comparator does not permit null elements
335	* @throws IllegalArgumentException {@inheritDoc}
336	*/
337	public SortedSet<E> subSet(E fromElement, E toElement) {
338	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
339	}
340
341	/**
342	* Equivalent to {@link #navigableHeadSet} but with a return type
343	* conforming to the <tt>SortedSet</tt> interface.
344	*
345	* <p>{@inheritDoc}
346	*
347	* @throws ClassCastException {@inheritDoc}
348	* @throws NullPointerException if <tt>toElement</tt> is null
349	* and this set uses natural ordering, or its comparator does
350	* not permit null elements
351	* @throws IllegalArgumentException {@inheritDoc}
352	*/
353	public SortedSet<E> headSet(E toElement) {
354	return new TreeSet<E>(m.navigableHeadMap(toElement));
355	}
356
357	/**
358	* Equivalent to {@link #navigableTailSet} but with a return type
359	* conforming to the <tt>SortedSet</tt> interface.
360	*
361	* <p>{@inheritDoc}
362	*
363	* @throws ClassCastException {@inheritDoc}
364	* @throws NullPointerException if <tt>fromElement</tt> is null
365	* and this set uses natural ordering, or its comparator does
366	* not permit null elements
367	* @throws IllegalArgumentException {@inheritDoc}
368	*/
369	public SortedSet<E> tailSet(E fromElement) {
370	return new TreeSet<E>(m.navigableTailMap(fromElement));
371	}
372
373	public Comparator<? super E> comparator() {
374	return m.comparator();
375	}
376
377	/**
378	* @throws NoSuchElementException {@inheritDoc}
379	*/
380	public E first() {
381	return m.firstKey();
382	}
383
384	/**
385	* @throws NoSuchElementException {@inheritDoc}
386	*/
387	public E last() {
388	return m.lastKey();
389	}
390
391	// NavigableSet API methods
392
393	/**
394	* @throws ClassCastException {@inheritDoc}
395	* @throws NullPointerException if the specified element is null
396	* and this set uses natural ordering, or its comparator
397	* does not permit null elements
398	* @since 1.6
399	*/
400	public E lower(E e) {
401	return m.lowerKey(e);
402	}
403
404	/**
405	* @throws ClassCastException {@inheritDoc}
406	* @throws NullPointerException if the specified element is null
407	* and this set uses natural ordering, or its comparator
408	* does not permit null elements
409	* @since 1.6
410	*/
411	public E floor(E e) {
412	return m.floorKey(e);
413	}
414
415	/**
416	* @throws ClassCastException {@inheritDoc}
417	* @throws NullPointerException if the specified element is null
418	* and this set uses natural ordering, or its comparator
419	* does not permit null elements
420	* @since 1.6
421	*/
422	public E ceiling(E e) {
423	return m.ceilingKey(e);
424	}
425
426	/**
427	* @throws ClassCastException {@inheritDoc}
428	* @throws NullPointerException if the specified element is null
429	* and this set uses natural ordering, or its comparator
430	* does not permit null elements
431	* @since 1.6
432	*/
433	public E higher(E e) {
434	return m.higherKey(e);
435	}
436
437	/**
438	* @since 1.6
439	*/
440	public E pollFirst() {
441	Map.Entry<E,?> e = m.pollFirstEntry();
442	return (e == null)? null : e.getKey();
443	}
444
445	/**
446	* @since 1.6
447	*/
448	public E pollLast() {
449	Map.Entry<E,?> e = m.pollLastEntry();
450	return (e == null)? null : e.getKey();
451	}
452
453	/**
454	* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
455	* themselves are not cloned.)
456	*
457	* @return a shallow copy of this set
458	*/
459	public Object clone() {
460	TreeSet<E> clone = null;
461	try {
462	clone = (TreeSet<E>) super.clone();
463	} catch (CloneNotSupportedException e) {
464	throw new InternalError();
465	}
466
467	clone.m = new TreeMap<E,Object>(m);
468
469	return clone;
470	}
471
472	/**
473	* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
474	* serialize it).
475	*
476	* @serialData Emits the comparator used to order this set, or
477	* <tt>null</tt> if it obeys its elements' natural ordering
478	* (Object), followed by the size of the set (the number of
479	* elements it contains) (int), followed by all of its
480	* elements (each an Object) in order (as determined by the
481	* set's Comparator, or by the elements' natural ordering if
482	* the set has no Comparator).
483	*/
484	private void writeObject(java.io.ObjectOutputStream s)
485	throws java.io.IOException {
486	// Write out any hidden stuff
487	s.defaultWriteObject();
488
489	// Write out Comparator
490	s.writeObject(m.comparator());
491
492	// Write out size
493	s.writeInt(m.size());
494
495	// Write out all elements in the proper order.
496	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
497	s.writeObject(i.next());
498	}
499
500	/**
501	* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
502	* deserialize it).
503	*/
504	private void readObject(java.io.ObjectInputStream s)
505	throws java.io.IOException, ClassNotFoundException {
506	// Read in any hidden stuff
507	s.defaultReadObject();
508
509	// Read in Comparator
510	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
511
512	// Create backing TreeMap
513	TreeMap<E,Object> tm;
514	if (c==null)
515	tm = new TreeMap<E,Object>();
516	else
517	tm = new TreeMap<E,Object>(c);
518	m = tm;
519
520	// Read in size
521	int size = s.readInt();
522
523	tm.readTreeSet(size, s, PRESENT);
524	}
525
526	private static final long serialVersionUID = -2479143000061671589L;
527	}