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;

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

    /**
     * Returns an iterator over the elements in this set.  The elements
     * are returned in descending order.
     *
     * @return an iterator over the elements in this set
     */
    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.
     *
     * @param o the 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 and is non-empty, 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.
     *
     * @param e element to be added to this set
     * @return <tt>true</tt> if the set did not already contain 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 and is non-empty, 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.
     *
     * @param o object to be removed from this set, if present
     * @return <tt>true</tt> if the set contained 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 and is non-empty, 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 elements to be added
     * @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 and is non-empty,
     *         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 and is non-empty,
     *         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 and is non-empty,
     *         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 and is non-empty,
     *         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:	1.12
Committed:	Tue May 17 04:10:23 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.11:	+12 -15 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
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><b>Note that this implementation is not synchronized.</b> If multiple
32	* threads access a set concurrently, and at least one of the threads modifies
33	* the set, it <i>must</i> be synchronized externally. This is typically
34	* accomplished by synchronizing on some object that naturally encapsulates
35	* the set. If no such object exists, the set should be "wrapped" using the
36	* <tt>Collections.synchronizedSet</tt> method. This is best done at creation
37	* time, to prevent accidental unsynchronized access to the set: <pre>
38	* SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
39	* </pre>
40	*
41	* <p>The iterators returned by this class's <tt>iterator</tt> method are
42	* <i>fail-fast</i>: if the set is modified at any time after the iterator is
43	* created, in any way except through the iterator's own <tt>remove</tt>
44	* method, the iterator will throw a {@link ConcurrentModificationException}.
45	* Thus, in the face of concurrent modification, the iterator fails quickly
46	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
47	* an undetermined time in the future.
48	*
49	* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
50	* as it is, generally speaking, impossible to make any hard guarantees in the
51	* presence of unsynchronized concurrent modification. Fail-fast iterators
52	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
53	* Therefore, it would be wrong to write a program that depended on this
54	* exception for its correctness: <i>the fail-fast behavior of iterators
55	* should be used only to detect bugs.</i>
56	*
57	* <p>This class is a member of the
58	* <a href="{@docRoot}/../guide/collections/index.html">
59	* Java Collections Framework</a>.
60	*
61	* @param <E> the type of elements maintained by this set
62	*
63	* @author Josh Bloch
64	* @version %I%, %G%
65	* @see Collection
66	* @see Set
67	* @see HashSet
68	* @see Comparable
69	* @see Comparator
70	* @see Collections#synchronizedSortedSet(SortedSet)
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. The elements
158	* are returned in ascending order.
159	*
160	* @return an iterator over the elements in this set
161	*/
162	public Iterator<E> iterator() {
163	return m.keySet().iterator();
164	}
165
166	/**
167	* Returns an iterator over the elements in this set. The elements
168	* are returned in descending order.
169	*
170	* @return an iterator over the elements in this set
171	*/
172	public Iterator<E> descendingIterator() {
173	return m.descendingKeySet().iterator();
174	}
175
176	/**
177	* Returns the number of elements in this set (its cardinality).
178	*
179	* @return the number of elements in this set (its cardinality)
180	*/
181	public int size() {
182	return m.size();
183	}
184
185	/**
186	* Returns <tt>true</tt> if this set contains no elements.
187	*
188	* @return <tt>true</tt> if this set contains no elements
189	*/
190	public boolean isEmpty() {
191	return m.isEmpty();
192	}
193
194	/**
195	* Returns <tt>true</tt> if this set contains the specified element.
196	*
197	* @param o the object to be checked for containment in this set
198	* @return <tt>true</tt> if this set contains the specified element
199	* @throws ClassCastException if the specified object cannot be compared
200	* with the elements currently in the set
201	* @throws NullPointerException if the specified element is null and
202	* this set uses natural ordering and is non-empty, or its
203	* comparator does not permit null elements
204	*/
205	public boolean contains(Object o) {
206	return m.containsKey(o);
207	}
208
209	/**
210	* Adds the specified element to this set if it is not already present.
211	*
212	* @param e element to be added to this set
213	* @return <tt>true</tt> if the set did not already contain the specified
214	* element
215	* @throws ClassCastException if the specified object cannot be compared
216	* with the elements currently in the set
217	* @throws NullPointerException if the specified element is null and
218	* this set uses natural ordering and is non-empty, or its
219	* comparator does not permit null elements
220	*/
221	public boolean add(E e) {
222	return m.put(e, PRESENT)==null;
223	}
224
225	/**
226	* Removes the specified element from this set if it is present.
227	*
228	* @param o object to be removed from this set, if present
229	* @return <tt>true</tt> if the set contained the specified element
230	* @throws ClassCastException if the specified object cannot be compared
231	* with the elements currently in the set
232	* @throws NullPointerException if the specified element is null and
233	* this set uses natural ordering and is non-empty, or its
234	* comparator does not permit null elements
235	*/
236	public boolean remove(Object o) {
237	return m.remove(o)==PRESENT;
238	}
239
240	/**
241	* Removes all of the elements from this set.
242	* The set will be empty after this call returns.
243	*/
244	public void clear() {
245	m.clear();
246	}
247
248	/**
249	* Adds all of the elements in the specified collection to this set.
250	*
251	* @param c elements to be added
252	* @return <tt>true</tt> if this set changed as a result of the call
253	* @throws ClassCastException if the elements provided cannot be compared
254	* with the elements currently in the set
255	* @throws NullPointerException if the specified collection is null or
256	* if any element is null and this set uses natural ordering, or
257	* its comparator does not permit null elements
258	*/
259	public boolean addAll(Collection<? extends E> c) {
260	// Use linear-time version if applicable
261	if (m.size()==0 && c.size() > 0 &&
262	c instanceof SortedSet &&
263	m instanceof TreeMap) {
264	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
265	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
266	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
267	Comparator<? super E> mc = map.comparator();
268	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
269	map.addAllForTreeSet(set, PRESENT);
270	return true;
271	}
272	}
273	return super.addAll(c);
274	}
275
276	/**
277	* @throws ClassCastException {@inheritDoc}
278	* @throws NullPointerException if <tt>fromElement</tt> or
279	* <tt>toElement</tt> is null and this set uses natural ordering,
280	* or its comparator does not permit null elements
281	* @throws IllegalArgumentException {@inheritDoc}
282	*/
283	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
284	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
285	}
286
287	/**
288	* @throws ClassCastException {@inheritDoc}
289	* @throws NullPointerException if <tt>toElement</tt> is null and
290	* this set uses natural ordering, or its comparator does
291	* not permit null elements
292	* @throws IllegalArgumentException {@inheritDoc}
293	*/
294	public NavigableSet<E> navigableHeadSet(E toElement) {
295	return new TreeSet<E>(m.navigableHeadMap(toElement));
296	}
297
298	/**
299	* @throws ClassCastException {@inheritDoc}
300	* @throws NullPointerException if <tt>fromElement</tt> is null and
301	* this set uses natural ordering, or its comparator does
302	* not permit null elements
303	* @throws IllegalArgumentException {@inheritDoc}
304	*/
305	public NavigableSet<E> navigableTailSet(E fromElement) {
306	return new TreeSet<E>(m.navigableTailMap(fromElement));
307	}
308
309	/**
310	* Equivalent to {@link #navigableSubSet} but with a return type
311	* conforming to the <tt>SortedSet</tt> interface.
312	*
313	* <p>{@inheritDoc}
314	*
315	* @throws ClassCastException {@inheritDoc}
316	* @throws NullPointerException if <tt>fromElement</tt> or
317	* <tt>toElement</tt> is null and this set uses natural ordering,
318	* or its comparator does not permit null elements
319	* @throws IllegalArgumentException {@inheritDoc}
320	*/
321	public SortedSet<E> subSet(E fromElement, E toElement) {
322	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
323	}
324
325	/**
326	* Equivalent to {@link #navigableHeadSet} 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>toElement</tt> is null
333	* and this set uses natural ordering, or its comparator does
334	* not permit null elements
335	* @throws IllegalArgumentException {@inheritDoc}
336	*/
337	public SortedSet<E> headSet(E toElement) {
338	return new TreeSet<E>(m.navigableHeadMap(toElement));
339	}
340
341	/**
342	* Equivalent to {@link #navigableTailSet} 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>fromElement</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> tailSet(E fromElement) {
354	return new TreeSet<E>(m.navigableTailMap(fromElement));
355	}
356
357	public Comparator<? super E> comparator() {
358	return m.comparator();
359	}
360
361	/**
362	* @throws NoSuchElementException {@inheritDoc}
363	*/
364	public E first() {
365	return m.firstKey();
366	}
367
368	/**
369	* @throws NoSuchElementException {@inheritDoc}
370	*/
371	public E last() {
372	return m.lastKey();
373	}
374
375	// NavigableSet API methods
376
377	/**
378	* @throws ClassCastException {@inheritDoc}
379	* @throws NullPointerException if the specified element is null and
380	* this set uses natural ordering and is non-empty,
381	* or its comparator does not permit null elements
382	*/
383	public E lower(E e) {
384	return m.lowerKey(e);
385	}
386
387	/**
388	* @throws ClassCastException {@inheritDoc}
389	* @throws NullPointerException if the specified element is null and
390	* this set uses natural ordering and is non-empty,
391	* or its comparator does not permit null elements
392	*/
393	public E floor(E e) {
394	return m.floorKey(e);
395	}
396
397	/**
398	* @throws ClassCastException {@inheritDoc}
399	* @throws NullPointerException if the specified element is null and
400	* this set uses natural ordering and is non-empty,
401	* or its comparator does not permit null elements
402	*/
403	public E ceiling(E e) {
404	return m.ceilingKey(e);
405	}
406
407	/**
408	* @throws ClassCastException {@inheritDoc}
409	* @throws NullPointerException if the specified element is null and
410	* this set uses natural ordering and is non-empty,
411	* or its comparator does not permit null elements
412	*/
413	public E higher(E e) {
414	return m.higherKey(e);
415	}
416
417	public E pollFirst() {
418	Map.Entry<E,?> e = m.pollFirstEntry();
419	return (e == null)? null : e.getKey();
420	}
421
422	public E pollLast() {
423	Map.Entry<E,?> e = m.pollLastEntry();
424	return (e == null)? null : e.getKey();
425	}
426
427	/**
428	* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
429	* themselves are not cloned.)
430	*
431	* @return a shallow copy of this set
432	*/
433	public Object clone() {
434	TreeSet<E> clone = null;
435	try {
436	clone = (TreeSet<E>) super.clone();
437	} catch (CloneNotSupportedException e) {
438	throw new InternalError();
439	}
440
441	clone.m = new TreeMap<E,Object>(m);
442
443	return clone;
444	}
445
446	/**
447	* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
448	* serialize it).
449	*
450	* @serialData Emits the comparator used to order this set, or
451	* <tt>null</tt> if it obeys its elements' natural ordering
452	* (Object), followed by the size of the set (the number of
453	* elements it contains) (int), followed by all of its
454	* elements (each an Object) in order (as determined by the
455	* set's Comparator, or by the elements' natural ordering if
456	* the set has no Comparator).
457	*/
458	private void writeObject(java.io.ObjectOutputStream s)
459	throws java.io.IOException {
460	// Write out any hidden stuff
461	s.defaultWriteObject();
462
463	// Write out Comparator
464	s.writeObject(m.comparator());
465
466	// Write out size
467	s.writeInt(m.size());
468
469	// Write out all elements in the proper order.
470	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
471	s.writeObject(i.next());
472	}
473
474	/**
475	* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
476	* deserialize it).
477	*/
478	private void readObject(java.io.ObjectInputStream s)
479	throws java.io.IOException, ClassNotFoundException {
480	// Read in any hidden stuff
481	s.defaultReadObject();
482
483	// Read in Comparator
484	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
485
486	// Create backing TreeMap
487	TreeMap<E,Object> tm;
488	if (c==null)
489	tm = new TreeMap<E,Object>();
490	else
491	tm = new TreeMap<E,Object>(c);
492	m = tm;
493
494	// Read in size
495	int size = s.readInt();
496
497	tm.readTreeSet(size, s, PRESENT);
498	}
499
500	private static final long serialVersionUID = -2479143000061671589L;
501	}