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 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:	1.13
Committed:	Tue May 17 07:29:01 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.12:	+4 -6 lines
Log Message:	doc fixes
#	User	Rev	Content
1	dl	1.1	/*
2			* %W% %E%
3			*
4	jsr166	1.6	* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5	dl	1.1	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6			*/
7
8	jsr166	1.8	package java.util;
9	dl	1.1
10			/**
11	jsr166	1.11	* 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	dl	1.1	*
16	jsr166	1.11	* <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	dl	1.1	*
19	jsr166	1.11	* <p>Note that the ordering maintained by a set (whether or not an explicit
20	dl	1.1	* 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	jsr166	1.11	* 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	dl	1.1	* 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	jsr166	1.11	* just fails to obey the general contract of the <tt>Set</tt> interface.
30	dl	1.1	*
31	jsr166	1.11	* <p><b>Note that this implementation is not synchronized.</b> If multiple
32	dl	1.1	* 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	jsr166	1.11	* </pre>
40	dl	1.1	*
41	jsr166	1.11	* <p>The iterators returned by this class's <tt>iterator</tt> method are
42	dl	1.1	* <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	jsr166	1.11	* method, the iterator will throw a {@link ConcurrentModificationException}.
45	dl	1.1	* 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	jsr166	1.10	* should be used only to detect bugs.</i>
56	dl	1.1	*
57	jsr166	1.10	* <p>This class is a member of the
58	dl	1.1	* <a href="{@docRoot}/../guide/collections/index.html">
59			* Java Collections Framework</a>.
60			*
61	jsr166	1.11	* @param <E> the type of elements maintained by this set
62			*
63	dl	1.1	* @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	jsr166	1.11	* Constructs a set backed by the specified navigable map.
86	dl	1.1	*/
87			private TreeSet(NavigableMap<E,Object> m) {
88			this.m = m;
89			}
90
91			/**
92	jsr166	1.11	* 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	dl	1.1	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
98	jsr166	1.11	* <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	dl	1.1	*/
104			public TreeSet() {
105			this(new TreeMap<E,Object>());
106			}
107
108			/**
109	jsr166	1.12	* 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	jsr166	1.11	*
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	dl	1.1	}
124
125			/**
126	jsr166	1.12	* 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	jsr166	1.11	* <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	dl	1.1	*/
139			public TreeSet(Collection<? extends E> c) {
140			this();
141			addAll(c);
142			}
143
144			/**
145	jsr166	1.11	* Constructs a new tree set containing the same elements and
146			* using the same ordering as the specified sorted set.
147	dl	1.1	*
148	jsr166	1.11	* @param s sorted set whose elements will comprise the new set
149			* @throws NullPointerException if the specified sorted set is null
150	dl	1.1	*/
151			public TreeSet(SortedSet<E> s) {
152			this(s.comparator());
153			addAll(s);
154			}
155
156			/**
157	jsr166	1.13	* Returns an iterator over the elements in this set in ascending order.
158	dl	1.1	*
159	jsr166	1.13	* @return an iterator over the elements in this set in ascending order
160	dl	1.1	*/
161			public Iterator<E> iterator() {
162	jsr166	1.11	return m.keySet().iterator();
163	dl	1.1	}
164
165			/**
166	jsr166	1.13	* Returns an iterator over the elements in this set in descending order.
167	dl	1.1	*
168	jsr166	1.13	* @return an iterator over the elements in this set in descending order
169	dl	1.1	*/
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	jsr166	1.11	* @return the number of elements in this set (its cardinality)
178	dl	1.1	*/
179			public int size() {
180			return m.size();
181			}
182
183			/**
184			* Returns <tt>true</tt> if this set contains no elements.
185			*
186	jsr166	1.11	* @return <tt>true</tt> if this set contains no elements
187	dl	1.1	*/
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	jsr166	1.11	* @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	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
198	jsr166	1.11	* 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	dl	1.1	*/
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	jsr166	1.11	* @param e element to be added to this set
211	dl	1.1	* @return <tt>true</tt> if the set did not already contain the specified
212	jsr166	1.11	* element
213	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
214	jsr166	1.11	* 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	dl	1.1	*/
219	jsr166	1.7	public boolean add(E e) {
220			return m.put(e, PRESENT)==null;
221	dl	1.1	}
222
223			/**
224			* Removes the specified element from this set if it is present.
225			*
226	jsr166	1.11	* @param o object to be removed from this set, if present
227			* @return <tt>true</tt> if the set contained the specified element
228	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
229	jsr166	1.11	* 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	dl	1.1	*/
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	jsr166	1.11	* The set will be empty after this call returns.
241	dl	1.1	*/
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 elements to be added
250	jsr166	1.11	* @return <tt>true</tt> if this set changed as a result of the call
251	dl	1.1	* @throws ClassCastException if the elements provided cannot be compared
252	jsr166	1.11	* 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	dl	1.1	*/
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	jsr166	1.9	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
263	dl	1.1	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
264	jsr166	1.9	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
265	dl	1.1	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	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
276	dl	1.1	* @throws NullPointerException if <tt>fromElement</tt> or
277	jsr166	1.11	* <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	dl	1.1	*/
281	dl	1.3	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
282			return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
283	dl	1.1	}
284
285			/**
286	jsr166	1.11	* @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	dl	1.1	*/
292	dl	1.3	public NavigableSet<E> navigableHeadSet(E toElement) {
293			return new TreeSet<E>(m.navigableHeadMap(toElement));
294	dl	1.1	}
295
296			/**
297	jsr166	1.11	* @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	dl	1.1	*/
303	dl	1.3	public NavigableSet<E> navigableTailSet(E fromElement) {
304			return new TreeSet<E>(m.navigableTailMap(fromElement));
305			}
306
307			/**
308	jsr166	1.11	* 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	dl	1.3	* @throws NullPointerException if <tt>fromElement</tt> or
315	jsr166	1.11	* <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	dl	1.3	*/
319			public SortedSet<E> subSet(E fromElement, E toElement) {
320			return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
321			}
322
323			/**
324	jsr166	1.11	* Equivalent to {@link #navigableHeadSet} but with a return type
325			* conforming to the <tt>SortedSet</tt> interface.
326			*
327			* <p>{@inheritDoc}
328	dl	1.3	*
329	jsr166	1.11	* @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	dl	1.3	*/
335			public SortedSet<E> headSet(E toElement) {
336			return new TreeSet<E>(m.navigableHeadMap(toElement));
337			}
338
339			/**
340	jsr166	1.11	* 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	dl	1.3	*/
351			public SortedSet<E> tailSet(E fromElement) {
352			return new TreeSet<E>(m.navigableTailMap(fromElement));
353	dl	1.1	}
354
355			public Comparator<? super E> comparator() {
356			return m.comparator();
357			}
358
359			/**
360	jsr166	1.11	* @throws NoSuchElementException {@inheritDoc}
361	dl	1.1	*/
362			public E first() {
363			return m.firstKey();
364			}
365
366			/**
367	jsr166	1.11	* @throws NoSuchElementException {@inheritDoc}
368	dl	1.1	*/
369			public E last() {
370			return m.lastKey();
371			}
372
373			// NavigableSet API methods
374
375			/**
376	jsr166	1.11	* @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	dl	1.1	*/
381	jsr166	1.11	public E lower(E e) {
382			return m.lowerKey(e);
383	dl	1.1	}
384
385			/**
386	jsr166	1.11	* @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	dl	1.1	*/
391	jsr166	1.11	public E floor(E e) {
392			return m.floorKey(e);
393	dl	1.1	}
394
395			/**
396	jsr166	1.11	* @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	dl	1.1	*/
401	jsr166	1.11	public E ceiling(E e) {
402			return m.ceilingKey(e);
403	dl	1.1	}
404
405			/**
406	jsr166	1.11	* @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	dl	1.1	*/
411	jsr166	1.7	public E higher(E e) {
412			return m.higherKey(e);
413	dl	1.1	}
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	jsr166	1.11	* @return a shallow copy of this set
430	dl	1.1	*/
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	jsr166	1.11	* <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	dl	1.1	* 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	jsr166	1.9	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
483	dl	1.1
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			}