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:	1.11
Committed:	Mon May 16 08:13:36 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.10:	+161 -329 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	1.11	* Constructs a new, empty tree set, sorted according to the
110			* specified comparator. All elements inserted into the set must
111			* be <i>mutually comparable</i> by the specified comparator:
112			* <tt>comparator.compare(e1, e2)</tt> must not throw a
113			* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
114			* <tt>e2</tt> in the set. If the user attempts to add an element
115			* to the set that violates this constraint, the
116			* <tt>add(Object)</tt> call will throw a
117			* <tt>ClassCastException</tt>.
118			*
119			* @param comparator the comparator that will be used to order this set.
120			* If <tt>null</tt>, the {@linkplain Comparable natural
121			* ordering} of the elements will be used.
122			*/
123			public TreeSet(Comparator<? super E> comparator) {
124			this(new TreeMap<E,Object>(comparator));
125	dl	1.1	}
126
127			/**
128	jsr166	1.11	* Constructs a new tree set containing the elements in the
129			* specified collection, sorted according to the <i>natural
130			* ordering</i> of its elements. All elements inserted into the
131			* set must implement the {@link Comparable} interface.
132			* Furthermore, all such elements must be <i>mutually
133			* comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
134			* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
135			* <tt>e2</tt> in the set.
136			*
137			* @param c collection whose elements will comprise the new set
138			* @throws ClassCastException if the elements in <tt>c</tt> are
139			* not {@link Comparable}, or are not mutually comparable
140			* @throws NullPointerException if the specified collection is null
141	dl	1.1	*/
142			public TreeSet(Collection<? extends E> c) {
143			this();
144			addAll(c);
145			}
146
147			/**
148	jsr166	1.11	* Constructs a new tree set containing the same elements and
149			* using the same ordering as the specified sorted set.
150	dl	1.1	*
151	jsr166	1.11	* @param s sorted set whose elements will comprise the new set
152			* @throws NullPointerException if the specified sorted set is null
153	dl	1.1	*/
154			public TreeSet(SortedSet<E> s) {
155			this(s.comparator());
156			addAll(s);
157			}
158
159			/**
160			* Returns an iterator over the elements in this set. The elements
161			* are returned in ascending order.
162			*
163	jsr166	1.11	* @return an iterator over the elements in this set
164	dl	1.1	*/
165			public Iterator<E> iterator() {
166	jsr166	1.11	return m.keySet().iterator();
167	dl	1.1	}
168
169			/**
170			* Returns an iterator over the elements in this set. The elements
171			* are returned in descending order.
172			*
173	jsr166	1.11	* @return an iterator over the elements in this set
174	dl	1.1	*/
175			public Iterator<E> descendingIterator() {
176			return m.descendingKeySet().iterator();
177			}
178
179			/**
180			* Returns the number of elements in this set (its cardinality).
181			*
182	jsr166	1.11	* @return the number of elements in this set (its cardinality)
183	dl	1.1	*/
184			public int size() {
185			return m.size();
186			}
187
188			/**
189			* Returns <tt>true</tt> if this set contains no elements.
190			*
191	jsr166	1.11	* @return <tt>true</tt> if this set contains no elements
192	dl	1.1	*/
193			public boolean isEmpty() {
194			return m.isEmpty();
195			}
196
197			/**
198			* Returns <tt>true</tt> if this set contains the specified element.
199			*
200	jsr166	1.11	* @param o the object to be checked for containment in this set
201			* @return <tt>true</tt> if this set contains the specified element
202	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
203	jsr166	1.11	* with the elements currently in the set
204			* @throws NullPointerException if the specified element is null and
205			* this set uses natural ordering and is non-empty, or its
206			* comparator does not permit null elements
207	dl	1.1	*/
208			public boolean contains(Object o) {
209			return m.containsKey(o);
210			}
211
212			/**
213			* Adds the specified element to this set if it is not already present.
214			*
215	jsr166	1.11	* @param e element to be added to this set
216	dl	1.1	* @return <tt>true</tt> if the set did not already contain the specified
217	jsr166	1.11	* element
218	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
219	jsr166	1.11	* with the elements currently in the set
220			* @throws NullPointerException if the specified element is null and
221			* this set uses natural ordering and is non-empty, or its
222			* comparator does not permit null elements
223	dl	1.1	*/
224	jsr166	1.7	public boolean add(E e) {
225			return m.put(e, PRESENT)==null;
226	dl	1.1	}
227
228			/**
229			* Removes the specified element from this set if it is present.
230			*
231	jsr166	1.11	* @param o object to be removed from this set, if present
232			* @return <tt>true</tt> if the set contained the specified element
233	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
234	jsr166	1.11	* with the elements currently in the set
235			* @throws NullPointerException if the specified element is null and
236			* this set uses natural ordering and is non-empty, or its
237			* comparator does not permit null elements
238	dl	1.1	*/
239			public boolean remove(Object o) {
240			return m.remove(o)==PRESENT;
241			}
242
243			/**
244			* Removes all of the elements from this set.
245	jsr166	1.11	* The set will be empty after this call returns.
246	dl	1.1	*/
247			public void clear() {
248			m.clear();
249			}
250
251			/**
252			* Adds all of the elements in the specified collection to this set.
253			*
254			* @param c elements to be added
255	jsr166	1.11	* @return <tt>true</tt> if this set changed as a result of the call
256	dl	1.1	* @throws ClassCastException if the elements provided cannot be compared
257	jsr166	1.11	* with the elements currently in the set
258			* @throws NullPointerException if the specified collection is null or
259			* if any element is null and this set uses natural ordering, or
260			* its comparator does not permit null elements
261	dl	1.1	*/
262			public boolean addAll(Collection<? extends E> c) {
263			// Use linear-time version if applicable
264			if (m.size()==0 && c.size() > 0 &&
265			c instanceof SortedSet &&
266			m instanceof TreeMap) {
267	jsr166	1.9	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
268	dl	1.1	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
269	jsr166	1.9	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
270	dl	1.1	Comparator<? super E> mc = map.comparator();
271			if (cc==mc \|\| (cc != null && cc.equals(mc))) {
272			map.addAllForTreeSet(set, PRESENT);
273			return true;
274			}
275			}
276			return super.addAll(c);
277			}
278
279			/**
280	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
281	dl	1.1	* @throws NullPointerException if <tt>fromElement</tt> or
282	jsr166	1.11	* <tt>toElement</tt> is null and this set uses natural ordering,
283			* or its comparator does not permit null elements
284			* @throws IllegalArgumentException {@inheritDoc}
285	dl	1.1	*/
286	dl	1.3	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
287			return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
288	dl	1.1	}
289
290			/**
291	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
292			* @throws NullPointerException if <tt>toElement</tt> is null and
293			* this set uses natural ordering, or its comparator does
294			* not permit null elements
295			* @throws IllegalArgumentException {@inheritDoc}
296	dl	1.1	*/
297	dl	1.3	public NavigableSet<E> navigableHeadSet(E toElement) {
298			return new TreeSet<E>(m.navigableHeadMap(toElement));
299	dl	1.1	}
300
301			/**
302	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
303			* @throws NullPointerException if <tt>fromElement</tt> is null and
304			* this set uses natural ordering, or its comparator does
305			* not permit null elements
306			* @throws IllegalArgumentException {@inheritDoc}
307	dl	1.1	*/
308	dl	1.3	public NavigableSet<E> navigableTailSet(E fromElement) {
309			return new TreeSet<E>(m.navigableTailMap(fromElement));
310			}
311
312			/**
313	jsr166	1.11	* Equivalent to {@link #navigableSubSet} but with a return type
314			* conforming to the <tt>SortedSet</tt> interface.
315			*
316			* <p>{@inheritDoc}
317			*
318			* @throws ClassCastException {@inheritDoc}
319	dl	1.3	* @throws NullPointerException if <tt>fromElement</tt> or
320	jsr166	1.11	* <tt>toElement</tt> is null and this set uses natural ordering,
321			* or its comparator does not permit null elements
322			* @throws IllegalArgumentException {@inheritDoc}
323	dl	1.3	*/
324			public SortedSet<E> subSet(E fromElement, E toElement) {
325			return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
326			}
327
328			/**
329	jsr166	1.11	* Equivalent to {@link #navigableHeadSet} but with a return type
330			* conforming to the <tt>SortedSet</tt> interface.
331			*
332			* <p>{@inheritDoc}
333	dl	1.3	*
334	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
335			* @throws NullPointerException if <tt>toElement</tt> is null
336			* and this set uses natural ordering, or its comparator does
337			* not permit null elements
338			* @throws IllegalArgumentException {@inheritDoc}
339	dl	1.3	*/
340			public SortedSet<E> headSet(E toElement) {
341			return new TreeSet<E>(m.navigableHeadMap(toElement));
342			}
343
344			/**
345	jsr166	1.11	* Equivalent to {@link #navigableTailSet} but with a return type
346			* conforming to the <tt>SortedSet</tt> interface.
347			*
348			* <p>{@inheritDoc}
349			*
350			* @throws ClassCastException {@inheritDoc}
351			* @throws NullPointerException if <tt>fromElement</tt> is null
352			* and this set uses natural ordering, or its comparator does
353			* not permit null elements
354			* @throws IllegalArgumentException {@inheritDoc}
355	dl	1.3	*/
356			public SortedSet<E> tailSet(E fromElement) {
357			return new TreeSet<E>(m.navigableTailMap(fromElement));
358	dl	1.1	}
359
360			public Comparator<? super E> comparator() {
361			return m.comparator();
362			}
363
364			/**
365	jsr166	1.11	* @throws NoSuchElementException {@inheritDoc}
366	dl	1.1	*/
367			public E first() {
368			return m.firstKey();
369			}
370
371			/**
372	jsr166	1.11	* @throws NoSuchElementException {@inheritDoc}
373	dl	1.1	*/
374			public E last() {
375			return m.lastKey();
376			}
377
378			// NavigableSet API methods
379
380			/**
381	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
382			* @throws NullPointerException if the specified element is null and
383			* this set uses natural ordering and is non-empty,
384			* or its comparator does not permit null elements
385	dl	1.1	*/
386	jsr166	1.11	public E lower(E e) {
387			return m.lowerKey(e);
388	dl	1.1	}
389
390			/**
391	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
392			* @throws NullPointerException if the specified element is null and
393			* this set uses natural ordering and is non-empty,
394			* or its comparator does not permit null elements
395	dl	1.1	*/
396	jsr166	1.11	public E floor(E e) {
397			return m.floorKey(e);
398	dl	1.1	}
399
400			/**
401	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
402			* @throws NullPointerException if the specified element is null and
403			* this set uses natural ordering and is non-empty,
404			* or its comparator does not permit null elements
405	dl	1.1	*/
406	jsr166	1.11	public E ceiling(E e) {
407			return m.ceilingKey(e);
408	dl	1.1	}
409
410			/**
411	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
412			* @throws NullPointerException if the specified element is null and
413			* this set uses natural ordering and is non-empty,
414			* or its comparator does not permit null elements
415	dl	1.1	*/
416	jsr166	1.7	public E higher(E e) {
417			return m.higherKey(e);
418	dl	1.1	}
419
420			public E pollFirst() {
421			Map.Entry<E,?> e = m.pollFirstEntry();
422			return (e == null)? null : e.getKey();
423			}
424
425			public E pollLast() {
426			Map.Entry<E,?> e = m.pollLastEntry();
427			return (e == null)? null : e.getKey();
428			}
429
430			/**
431			* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
432			* themselves are not cloned.)
433			*
434	jsr166	1.11	* @return a shallow copy of this set
435	dl	1.1	*/
436			public Object clone() {
437			TreeSet<E> clone = null;
438			try {
439			clone = (TreeSet<E>) super.clone();
440			} catch (CloneNotSupportedException e) {
441			throw new InternalError();
442			}
443
444			clone.m = new TreeMap<E,Object>(m);
445
446			return clone;
447			}
448
449			/**
450			* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
451			* serialize it).
452			*
453			* @serialData Emits the comparator used to order this set, or
454	jsr166	1.11	* <tt>null</tt> if it obeys its elements' natural ordering
455			* (Object), followed by the size of the set (the number of
456			* elements it contains) (int), followed by all of its
457			* elements (each an Object) in order (as determined by the
458			* set's Comparator, or by the elements' natural ordering if
459	dl	1.1	* the set has no Comparator).
460			*/
461			private void writeObject(java.io.ObjectOutputStream s)
462			throws java.io.IOException {
463			// Write out any hidden stuff
464			s.defaultWriteObject();
465
466			// Write out Comparator
467			s.writeObject(m.comparator());
468
469			// Write out size
470			s.writeInt(m.size());
471
472			// Write out all elements in the proper order.
473			for (Iterator i=m.keySet().iterator(); i.hasNext(); )
474			s.writeObject(i.next());
475			}
476
477			/**
478			* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
479			* deserialize it).
480			*/
481			private void readObject(java.io.ObjectInputStream s)
482			throws java.io.IOException, ClassNotFoundException {
483			// Read in any hidden stuff
484			s.defaultReadObject();
485
486			// Read in Comparator
487	jsr166	1.9	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
488	dl	1.1
489			// Create backing TreeMap
490			TreeMap<E,Object> tm;
491			if (c==null)
492			tm = new TreeMap<E,Object>();
493			else
494			tm = new TreeMap<E,Object>(c);
495			m = tm;
496
497			// Read in size
498			int size = s.readInt();
499
500			tm.readTreeSet(size, s, PRESENT);
501			}
502
503			private static final long serialVersionUID = -2479143000061671589L;
504			}