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 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.
     *
     * @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 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 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:	1.14
Committed:	Tue May 17 22:04:55 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.13:	+1 -1 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 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	*/
170	public Iterator<E> descendingIterator() {
171	return m.descendingKeySet().iterator();
172	}
173
174	/**
175	* Returns the number of elements in this set (its cardinality).
176	*
177	* @return the number of elements in this set (its cardinality)
178	*/
179	public int size() {
180	return m.size();
181	}
182
183	/**
184	* Returns <tt>true</tt> if this set contains no elements.
185	*
186	* @return <tt>true</tt> if this set contains no elements
187	*/
188	public boolean isEmpty() {
189	return m.isEmpty();
190	}
191
192	/**
193	* Returns <tt>true</tt> if this set contains the specified element.
194	*
195	* @param o the object to be checked for containment in this set
196	* @return <tt>true</tt> if this set contains the specified element
197	* @throws ClassCastException if the specified object cannot be compared
198	* with the elements currently in the set
199	* @throws NullPointerException if the specified element is null and
200	* this set uses natural ordering and is non-empty, or its
201	* comparator does not permit null elements
202	*/
203	public boolean contains(Object o) {
204	return m.containsKey(o);
205	}
206
207	/**
208	* Adds the specified element to this set if it is not already present.
209	*
210	* @param e element to be added to this set
211	* @return <tt>true</tt> if the set did not already contain the specified
212	* element
213	* @throws ClassCastException if the specified object cannot be compared
214	* with the elements currently in the set
215	* @throws NullPointerException if the specified element is null and
216	* this set uses natural ordering and is non-empty, or its
217	* comparator does not permit null elements
218	*/
219	public boolean add(E e) {
220	return m.put(e, PRESENT)==null;
221	}
222
223	/**
224	* Removes the specified element from this set if it is present.
225	*
226	* @param o object to be removed from this set, if present
227	* @return <tt>true</tt> if the set contained the specified element
228	* @throws ClassCastException if the specified object cannot be compared
229	* with the elements currently in the set
230	* @throws NullPointerException if the specified element is null and
231	* this set uses natural ordering and is non-empty, or its
232	* comparator does not permit null elements
233	*/
234	public boolean remove(Object o) {
235	return m.remove(o)==PRESENT;
236	}
237
238	/**
239	* Removes all of the elements from this set.
240	* The set will be empty after this call returns.
241	*/
242	public void clear() {
243	m.clear();
244	}
245
246	/**
247	* Adds all of the elements in the specified collection to this set.
248	*
249	* @param c collection containing elements to be added to this set
250	* @return <tt>true</tt> if this set changed as a result of the call
251	* @throws ClassCastException if the elements provided cannot be compared
252	* with the elements currently in the set
253	* @throws NullPointerException if the specified collection is null or
254	* if any element is null and this set uses natural ordering, or
255	* its comparator does not permit null elements
256	*/
257	public boolean addAll(Collection<? extends E> c) {
258	// Use linear-time version if applicable
259	if (m.size()==0 && c.size() > 0 &&
260	c instanceof SortedSet &&
261	m instanceof TreeMap) {
262	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
263	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
264	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
265	Comparator<? super E> mc = map.comparator();
266	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
267	map.addAllForTreeSet(set, PRESENT);
268	return true;
269	}
270	}
271	return super.addAll(c);
272	}
273
274	/**
275	* @throws ClassCastException {@inheritDoc}
276	* @throws NullPointerException if <tt>fromElement</tt> or
277	* <tt>toElement</tt> is null and this set uses natural ordering,
278	* or its comparator does not permit null elements
279	* @throws IllegalArgumentException {@inheritDoc}
280	*/
281	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
282	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
283	}
284
285	/**
286	* @throws ClassCastException {@inheritDoc}
287	* @throws NullPointerException if <tt>toElement</tt> is null and
288	* this set uses natural ordering, or its comparator does
289	* not permit null elements
290	* @throws IllegalArgumentException {@inheritDoc}
291	*/
292	public NavigableSet<E> navigableHeadSet(E toElement) {
293	return new TreeSet<E>(m.navigableHeadMap(toElement));
294	}
295
296	/**
297	* @throws ClassCastException {@inheritDoc}
298	* @throws NullPointerException if <tt>fromElement</tt> is null and
299	* this set uses natural ordering, or its comparator does
300	* not permit null elements
301	* @throws IllegalArgumentException {@inheritDoc}
302	*/
303	public NavigableSet<E> navigableTailSet(E fromElement) {
304	return new TreeSet<E>(m.navigableTailMap(fromElement));
305	}
306
307	/**
308	* Equivalent to {@link #navigableSubSet} but with a return type
309	* conforming to the <tt>SortedSet</tt> interface.
310	*
311	* <p>{@inheritDoc}
312	*
313	* @throws ClassCastException {@inheritDoc}
314	* @throws NullPointerException if <tt>fromElement</tt> or
315	* <tt>toElement</tt> is null and this set uses natural ordering,
316	* or its comparator does not permit null elements
317	* @throws IllegalArgumentException {@inheritDoc}
318	*/
319	public SortedSet<E> subSet(E fromElement, E toElement) {
320	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
321	}
322
323	/**
324	* Equivalent to {@link #navigableHeadSet} but with a return type
325	* conforming to the <tt>SortedSet</tt> interface.
326	*
327	* <p>{@inheritDoc}
328	*
329	* @throws ClassCastException {@inheritDoc}
330	* @throws NullPointerException if <tt>toElement</tt> is null
331	* and this set uses natural ordering, or its comparator does
332	* not permit null elements
333	* @throws IllegalArgumentException {@inheritDoc}
334	*/
335	public SortedSet<E> headSet(E toElement) {
336	return new TreeSet<E>(m.navigableHeadMap(toElement));
337	}
338
339	/**
340	* Equivalent to {@link #navigableTailSet} but with a return type
341	* conforming to the <tt>SortedSet</tt> interface.
342	*
343	* <p>{@inheritDoc}
344	*
345	* @throws ClassCastException {@inheritDoc}
346	* @throws NullPointerException if <tt>fromElement</tt> is null
347	* and this set uses natural ordering, or its comparator does
348	* not permit null elements
349	* @throws IllegalArgumentException {@inheritDoc}
350	*/
351	public SortedSet<E> tailSet(E fromElement) {
352	return new TreeSet<E>(m.navigableTailMap(fromElement));
353	}
354
355	public Comparator<? super E> comparator() {
356	return m.comparator();
357	}
358
359	/**
360	* @throws NoSuchElementException {@inheritDoc}
361	*/
362	public E first() {
363	return m.firstKey();
364	}
365
366	/**
367	* @throws NoSuchElementException {@inheritDoc}
368	*/
369	public E last() {
370	return m.lastKey();
371	}
372
373	// NavigableSet API methods
374
375	/**
376	* @throws ClassCastException {@inheritDoc}
377	* @throws NullPointerException if the specified element is null and
378	* this set uses natural ordering and is non-empty,
379	* or its comparator does not permit null elements
380	*/
381	public E lower(E e) {
382	return m.lowerKey(e);
383	}
384
385	/**
386	* @throws ClassCastException {@inheritDoc}
387	* @throws NullPointerException if the specified element is null and
388	* this set uses natural ordering and is non-empty,
389	* or its comparator does not permit null elements
390	*/
391	public E floor(E e) {
392	return m.floorKey(e);
393	}
394
395	/**
396	* @throws ClassCastException {@inheritDoc}
397	* @throws NullPointerException if the specified element is null and
398	* this set uses natural ordering and is non-empty,
399	* or its comparator does not permit null elements
400	*/
401	public E ceiling(E e) {
402	return m.ceilingKey(e);
403	}
404
405	/**
406	* @throws ClassCastException {@inheritDoc}
407	* @throws NullPointerException if the specified element is null and
408	* this set uses natural ordering and is non-empty,
409	* or its comparator does not permit null elements
410	*/
411	public E higher(E e) {
412	return m.higherKey(e);
413	}
414
415	public E pollFirst() {
416	Map.Entry<E,?> e = m.pollFirstEntry();
417	return (e == null)? null : e.getKey();
418	}
419
420	public E pollLast() {
421	Map.Entry<E,?> e = m.pollLastEntry();
422	return (e == null)? null : e.getKey();
423	}
424
425	/**
426	* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
427	* themselves are not cloned.)
428	*
429	* @return a shallow copy of this set
430	*/
431	public Object clone() {
432	TreeSet<E> clone = null;
433	try {
434	clone = (TreeSet<E>) super.clone();
435	} catch (CloneNotSupportedException e) {
436	throw new InternalError();
437	}
438
439	clone.m = new TreeMap<E,Object>(m);
440
441	return clone;
442	}
443
444	/**
445	* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
446	* serialize it).
447	*
448	* @serialData Emits the comparator used to order this set, or
449	* <tt>null</tt> if it obeys its elements' natural ordering
450	* (Object), followed by the size of the set (the number of
451	* elements it contains) (int), followed by all of its
452	* elements (each an Object) in order (as determined by the
453	* set's Comparator, or by the elements' natural ordering if
454	* the set has no Comparator).
455	*/
456	private void writeObject(java.io.ObjectOutputStream s)
457	throws java.io.IOException {
458	// Write out any hidden stuff
459	s.defaultWriteObject();
460
461	// Write out Comparator
462	s.writeObject(m.comparator());
463
464	// Write out size
465	s.writeInt(m.size());
466
467	// Write out all elements in the proper order.
468	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
469	s.writeObject(i.next());
470	}
471
472	/**
473	* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
474	* deserialize it).
475	*/
476	private void readObject(java.io.ObjectInputStream s)
477	throws java.io.IOException, ClassNotFoundException {
478	// Read in any hidden stuff
479	s.defaultReadObject();
480
481	// Read in Comparator
482	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
483
484	// Create backing TreeMap
485	TreeMap<E,Object> tm;
486	if (c==null)
487	tm = new TreeMap<E,Object>();
488	else
489	tm = new TreeMap<E,Object>(c);
490	m = tm;
491
492	// Read in size
493	int size = s.readInt();
494
495	tm.readTreeSet(size, s, PRESENT);
496	}
497
498	private static final long serialVersionUID = -2479143000061671589L;
499	}