java/util/TreeSet.java

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

package java.util;

/**
 * A {@link NavigableSet} implementation based on a {@link TreeMap}.
 * The elements are ordered using their {@linkplain Comparable natural
 * ordering}, or by a {@link Comparator} provided at set creation
 * time, depending on which constructor is used.
 *
 * <p>This implementation provides guaranteed log(n) time cost for the basic
 * operations (<tt>add</tt>, <tt>remove</tt> and <tt>contains</tt>).
 *
 * <p>Note that the ordering maintained by a set (whether or not an explicit
 * comparator is provided) must be <i>consistent with equals</i> if it is to
 * correctly implement the <tt>Set</tt> interface.  (See <tt>Comparable</tt>
 * or <tt>Comparator</tt> for a precise definition of <i>consistent with
 * equals</i>.)  This is so because the <tt>Set</tt> interface is defined in
 * terms of the <tt>equals</tt> operation, but a <tt>TreeSet</tt> instance
 * performs all element comparisons using its <tt>compareTo</tt> (or
 * <tt>compare</tt>) method, so two elements that are deemed equal by this method
 * are, from the standpoint of the set, equal.  The behavior of a set
 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it
 * just fails to obey the general contract of the <tt>Set</tt> interface.
 *
 * <p><strong>Note that this implementation is not synchronized.</strong>
 * If multiple threads access a tree set concurrently, and at least one
 * of the threads modifies the set, it <i>must</i> be synchronized
 * externally.  This is typically accomplished by synchronizing on some
 * object that naturally encapsulates the set.
 * If no such object exists, the set should be "wrapped" using the
 * {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
 * method.  This is best done at creation time, to prevent accidental
 * unsynchronized access to the set: <pre>
 *   SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
 *
 * <p>The iterators returned by this class's <tt>iterator</tt> method are
 * <i>fail-fast</i>: if the set is modified at any time after the iterator is
 * created, in any way except through the iterator's own <tt>remove</tt>
 * method, the iterator will throw a {@link ConcurrentModificationException}.
 * Thus, in the face of concurrent modification, the iterator fails quickly
 * and cleanly, rather than risking arbitrary, non-deterministic behavior at
 * an undetermined time in the future.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:   <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 *
 * @author  Josh Bloch
 * @version %I%, %G%
 * @see     Collection
 * @see     Set
 * @see     HashSet
 * @see     Comparable
 * @see     Comparator
 * @see     TreeMap
 * @since   1.2
 */

public class TreeSet<E>
    extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable
{
    private transient NavigableMap<E,Object> m; // The backing Map

    // Dummy value to associate with an Object in the backing Map
    private static final Object PRESENT = new Object();

    /**
     * Constructs a set backed by the specified navigable map.
     */
    private TreeSet(NavigableMap<E,Object> m) {
        this.m = m;
    }

    /**
     * Constructs a new, empty tree set, sorted according to the
     * natural ordering of its elements.  All elements inserted into
     * the set must implement the {@link Comparable} interface.
     * Furthermore, all such elements must be <i>mutually
     * comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
     * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
     * <tt>e2</tt> in the set.  If the user attempts to add an element
     * to the set that violates this constraint (for example, the user
     * attempts to add a string element to a set whose elements are
     * integers), the <tt>add(Object)</tt> call will throw a
     * <tt>ClassCastException</tt>.
     */
    public TreeSet() {
        this(new TreeMap<E,Object>());
    }

    /**
     * Constructs a new, empty tree set, sorted according to the specified
     * comparator.  All elements inserted into the set must be <i>mutually
     * comparable</i> by the specified comparator: <tt>comparator.compare(e1,
     * e2)</tt> must not throw a <tt>ClassCastException</tt> for any elements
     * <tt>e1</tt> and <tt>e2</tt> in the set.  If the user attempts to add
     * an element to the set that violates this constraint, the
     * <tt>add(Object)</tt> call will throw a <tt>ClassCastException</tt>.
     *
     * @param comparator the comparator that will be used to order this set.
     *        If <tt>null</tt>, the {@linkplain Comparable natural
     *        ordering} of the elements will be used.
     */
    public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<E,Object>(comparator));
    }

    /**
     * Constructs a new tree set containing the elements in the specified
     * collection, sorted according to the <i>natural ordering</i> of its
     * elements.  All elements inserted into the set must implement the
     * {@link Comparable} interface.  Furthermore, all such elements must be
     * <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
     * <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
     * <tt>e2</tt> in the set.
     *
     * @param c collection whose elements will comprise the new set
     * @throws ClassCastException if the elements in <tt>c</tt> are
     *         not {@link Comparable}, or are not mutually comparable
     * @throws NullPointerException if the specified collection is null
     */
    public TreeSet(Collection<? extends E> c) {
        this();
        addAll(c);
    }

    /**
     * Constructs a new tree set containing the same elements and
     * using the same ordering as the specified sorted set.
     *
     * @param s sorted set whose elements will comprise the new set
     * @throws NullPointerException if the specified sorted set is null
     */
    public TreeSet(SortedSet<E> s) {
        this(s.comparator());
        addAll(s);
    }

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

    /**
     * Returns an iterator over the elements in this set in descending order.
     *
     * @return an iterator over the elements in this set in descending order
     * @since 1.6
     */
    public Iterator<E> descendingIterator() {
        return m.descendingKeySet().iterator();
    }

    /**
     * Returns the number of elements in this set (its cardinality).
     *
     * @return the number of elements in this set (its cardinality)
     */
    public int size() {
        return m.size();
    }

    /**
     * Returns <tt>true</tt> if this set contains no elements.
     *
     * @return <tt>true</tt> if this set contains no elements
     */
    public boolean isEmpty() {
        return m.isEmpty();
    }

    /**
     * Returns <tt>true</tt> if this set contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this set
     * contains an element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o object to be checked for containment in this set
     * @return <tt>true</tt> if this set contains the specified element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in the set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean contains(Object o) {
        return m.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     * More formally, adds the specified element <tt>e</tt> to this set if
     * the set contains no element <tt>e2</tt> such that
     * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns <tt>false</tt>.
     *
     * @param e element to be added to this set
     * @return <tt>true</tt> if this set did not already contain the specified
     *         element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }

    /**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
     * if this set contains such an element.  Returns <tt>true</tt> if
     * this set contained the element (or equivalently, if this set
     * changed as a result of the call).  (This set will not contain the
     * element once the call returns.)
     *
     * @param o object to be removed from this set, if present
     * @return <tt>true</tt> if this set contained the specified element
     * @throws ClassCastException if the specified object cannot be compared
     *         with the elements currently in this set
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     */
    public boolean remove(Object o) {
        return m.remove(o)==PRESENT;
    }

    /**
     * Removes all of the elements from this set.
     * The set will be empty after this call returns.
     */
    public void clear() {
        m.clear();
    }

    /**
     * Adds all of the elements in the specified collection to this set.
     *
     * @param c collection containing elements to be added to this set
     * @return <tt>true</tt> if this set changed as a result of the call
     * @throws ClassCastException if the elements provided cannot be compared
     *         with the elements currently in the set
     * @throws NullPointerException if the specified collection is null or
     *         if any element is null and this set uses natural ordering, or
     *         its comparator does not permit null elements
     */
    public  boolean addAll(Collection<? extends E> c) {
        // Use linear-time version if applicable
        if (m.size()==0 && c.size() > 0 &&
            c instanceof SortedSet &&
            m instanceof TreeMap) {
            SortedSet<? extends E> set = (SortedSet<? extends E>) c;
            TreeMap<E,Object> map = (TreeMap<E, Object>) m;
            Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
            Comparator<? super E> mc = map.comparator();
            if (cc==mc || (cc != null && cc.equals(mc))) {
                map.addAllForTreeSet(set, PRESENT);
                return true;
            }
        }
        return super.addAll(c);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> or
     *         <tt>toElement</tt> is null and this set uses natural ordering,
     *         or its comparator does not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.6
     */
    public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
        return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>toElement</tt> is null and
     *         this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.6
     */
    public NavigableSet<E> navigableHeadSet(E toElement) {
        return new TreeSet<E>(m.navigableHeadMap(toElement));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> is null and
     *         this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     * @since 1.6
     */
    public NavigableSet<E> navigableTailSet(E fromElement) {
        return new TreeSet<E>(m.navigableTailMap(fromElement));
    }

    /**
     * Equivalent to {@link #navigableSubSet} but with a return type
     * conforming to the <tt>SortedSet</tt> interface.
     *
     * <p>{@inheritDoc}
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> or
     *         <tt>toElement</tt> is null and this set uses natural ordering,
     *         or its comparator does not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> subSet(E fromElement, E toElement) {
        return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
    }

    /**
     * Equivalent to {@link #navigableHeadSet} but with a return type
     * conforming to the <tt>SortedSet</tt> interface.
     *
     * <p>{@inheritDoc}
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>toElement</tt> is null
     *         and this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> headSet(E toElement) {
        return new TreeSet<E>(m.navigableHeadMap(toElement));
    }

    /**
     * Equivalent to {@link #navigableTailSet} but with a return type
     * conforming to the <tt>SortedSet</tt> interface.
     *
     * <p>{@inheritDoc}
     *
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if <tt>fromElement</tt> is null
     *         and this set uses natural ordering, or its comparator does
     *         not permit null elements
     * @throws IllegalArgumentException {@inheritDoc}
     */
    public SortedSet<E> tailSet(E fromElement) {
        return new TreeSet<E>(m.navigableTailMap(fromElement));
    }

    public Comparator<? super E> comparator() {
        return m.comparator();
    }

    /**
     * @throws NoSuchElementException {@inheritDoc}
     */
    public E first() {
        return m.firstKey();
    }

    /**
     * @throws NoSuchElementException {@inheritDoc}
     */
    public E last() {
        return m.lastKey();
    }

    // NavigableSet API methods

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E lower(E e) {
        return m.lowerKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E floor(E e) {
        return m.floorKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E ceiling(E e) {
        return m.ceilingKey(e);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     *         and this set uses natural ordering, or its comparator
     *         does not permit null elements
     * @since 1.6
     */
    public E higher(E e) {
        return m.higherKey(e);
    }

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

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

    /**
     * Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
     * themselves are not cloned.)
     *
     * @return a shallow copy of this set
     */
    public Object clone() {
        TreeSet<E> clone = null;
        try {
            clone = (TreeSet<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }

        clone.m = new TreeMap<E,Object>(m);

        return clone;
    }

    /**
     * Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
     * serialize it).
     *
     * @serialData Emits the comparator used to order this set, or
     *             <tt>null</tt> if it obeys its elements' natural ordering
     *             (Object), followed by the size of the set (the number of
     *             elements it contains) (int), followed by all of its
     *             elements (each an Object) in order (as determined by the
     *             set's Comparator, or by the elements' natural ordering if
     *             the set has no Comparator).
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        // Write out any hidden stuff
        s.defaultWriteObject();

        // Write out Comparator
        s.writeObject(m.comparator());

        // Write out size
        s.writeInt(m.size());

        // Write out all elements in the proper order.
        for (Iterator i=m.keySet().iterator(); i.hasNext(); )
            s.writeObject(i.next());
    }

    /**
     * Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
     * deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        // Read in any hidden stuff
        s.defaultReadObject();

        // Read in Comparator
        Comparator<? super E> c = (Comparator<? super E>) s.readObject();

        // Create backing TreeMap
        TreeMap<E,Object> tm;
        if (c==null)
            tm = new TreeMap<E,Object>();
        else
            tm = new TreeMap<E,Object>(c);
        m = tm;

        // Read in size
        int size = s.readInt();

        tm.readTreeSet(size, s, PRESENT);
    }

    private static final long serialVersionUID = -2479143000061671589L;
}
Revision:	1.20
Committed:	Tue Feb 7 20:54:24 2006 UTC (18 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.19:	+0 -1 lines
Log Message:	6378729: Remove workaround for 6280605
#	User	Rev	Content
1	dl	1.1	/*
2			* %W% %E%
3			*
4	jsr166	1.19	* Copyright 2006 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	1.18	* <p><strong>Note that this implementation is not synchronized.</strong>
32			* If multiple threads access a tree set concurrently, and at least one
33			* of the threads modifies the set, it <i>must</i> be synchronized
34			* externally. This is typically accomplished by synchronizing on some
35			* object that naturally encapsulates the set.
36			* If no such object exists, the set should be "wrapped" using the
37			* {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
38			* method. This is best done at creation time, to prevent accidental
39			* unsynchronized access to the set: <pre>
40			* SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
41	dl	1.1	*
42	jsr166	1.11	* <p>The iterators returned by this class's <tt>iterator</tt> method are
43	dl	1.1	* <i>fail-fast</i>: if the set is modified at any time after the iterator is
44			* created, in any way except through the iterator's own <tt>remove</tt>
45	jsr166	1.11	* method, the iterator will throw a {@link ConcurrentModificationException}.
46	dl	1.1	* Thus, in the face of concurrent modification, the iterator fails quickly
47			* and cleanly, rather than risking arbitrary, non-deterministic behavior at
48			* an undetermined time in the future.
49			*
50			* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
51			* as it is, generally speaking, impossible to make any hard guarantees in the
52			* presence of unsynchronized concurrent modification. Fail-fast iterators
53			* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
54			* Therefore, it would be wrong to write a program that depended on this
55			* exception for its correctness: <i>the fail-fast behavior of iterators
56	jsr166	1.10	* should be used only to detect bugs.</i>
57	dl	1.1	*
58	jsr166	1.10	* <p>This class is a member of the
59	dl	1.1	* <a href="{@docRoot}/../guide/collections/index.html">
60			* Java Collections Framework</a>.
61			*
62	jsr166	1.11	* @param <E> the type of elements maintained by this set
63			*
64	dl	1.1	* @author Josh Bloch
65			* @version %I%, %G%
66			* @see Collection
67			* @see Set
68			* @see HashSet
69			* @see Comparable
70			* @see Comparator
71			* @see TreeMap
72			* @since 1.2
73			*/
74
75			public class TreeSet<E>
76			extends AbstractSet<E>
77			implements NavigableSet<E>, Cloneable, java.io.Serializable
78			{
79			private transient NavigableMap<E,Object> m; // The backing Map
80
81			// Dummy value to associate with an Object in the backing Map
82			private static final Object PRESENT = new Object();
83
84			/**
85	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	jsr166	1.17	* @since 1.6
170	dl	1.1	*/
171			public Iterator<E> descendingIterator() {
172			return m.descendingKeySet().iterator();
173			}
174
175			/**
176			* Returns the number of elements in this set (its cardinality).
177			*
178	jsr166	1.11	* @return the number of elements in this set (its cardinality)
179	dl	1.1	*/
180			public int size() {
181			return m.size();
182			}
183
184			/**
185			* Returns <tt>true</tt> if this set contains no elements.
186			*
187	jsr166	1.11	* @return <tt>true</tt> if this set contains no elements
188	dl	1.1	*/
189			public boolean isEmpty() {
190			return m.isEmpty();
191			}
192
193			/**
194			* Returns <tt>true</tt> if this set contains the specified element.
195	jsr166	1.16	* More formally, returns <tt>true</tt> if and only if this set
196			* contains an element <tt>e</tt> such that
197			* <tt>(o==null ? e==null : o.equals(e))</tt>.
198	dl	1.1	*
199	jsr166	1.16	* @param o object to be checked for containment in this set
200	jsr166	1.11	* @return <tt>true</tt> if this set contains the specified element
201	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
202	jsr166	1.11	* with the elements currently in the set
203	jsr166	1.15	* @throws NullPointerException if the specified element is null
204			* and this set uses natural ordering, or its comparator
205			* does not permit null elements
206	dl	1.1	*/
207			public boolean contains(Object o) {
208			return m.containsKey(o);
209			}
210
211			/**
212			* Adds the specified element to this set if it is not already present.
213	jsr166	1.16	* More formally, adds the specified element <tt>e</tt> to this set if
214			* the set contains no element <tt>e2</tt> such that
215			* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
216			* If this set already contains the element, the call leaves the set
217			* unchanged and returns <tt>false</tt>.
218	dl	1.1	*
219	jsr166	1.11	* @param e element to be added to this set
220	jsr166	1.16	* @return <tt>true</tt> if this set did not already contain the specified
221	jsr166	1.11	* element
222	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
223	jsr166	1.16	* with the elements currently in this set
224	jsr166	1.15	* @throws NullPointerException if the specified element is null
225			* and this set uses natural ordering, or its comparator
226			* does not permit null elements
227	dl	1.1	*/
228	jsr166	1.7	public boolean add(E e) {
229			return m.put(e, PRESENT)==null;
230	dl	1.1	}
231
232			/**
233			* Removes the specified element from this set if it is present.
234	jsr166	1.16	* More formally, removes an element <tt>e</tt> such that
235			* <tt>(o==null ? e==null : o.equals(e))</tt>,
236			* if this set contains such an element. Returns <tt>true</tt> if
237			* this set contained the element (or equivalently, if this set
238			* changed as a result of the call). (This set will not contain the
239			* element once the call returns.)
240	dl	1.1	*
241	jsr166	1.11	* @param o object to be removed from this set, if present
242	jsr166	1.16	* @return <tt>true</tt> if this set contained the specified element
243	dl	1.1	* @throws ClassCastException if the specified object cannot be compared
244	jsr166	1.16	* with the elements currently in this set
245	jsr166	1.15	* @throws NullPointerException if the specified element is null
246			* and this set uses natural ordering, or its comparator
247			* does not permit null elements
248	dl	1.1	*/
249			public boolean remove(Object o) {
250			return m.remove(o)==PRESENT;
251			}
252
253			/**
254			* Removes all of the elements from this set.
255	jsr166	1.11	* The set will be empty after this call returns.
256	dl	1.1	*/
257			public void clear() {
258			m.clear();
259			}
260
261			/**
262			* Adds all of the elements in the specified collection to this set.
263			*
264	jsr166	1.14	* @param c collection containing elements to be added to this set
265	jsr166	1.11	* @return <tt>true</tt> if this set changed as a result of the call
266	dl	1.1	* @throws ClassCastException if the elements provided cannot be compared
267	jsr166	1.11	* with the elements currently in the set
268			* @throws NullPointerException if the specified collection is null or
269			* if any element is null and this set uses natural ordering, or
270			* its comparator does not permit null elements
271	dl	1.1	*/
272			public boolean addAll(Collection<? extends E> c) {
273			// Use linear-time version if applicable
274			if (m.size()==0 && c.size() > 0 &&
275			c instanceof SortedSet &&
276			m instanceof TreeMap) {
277	jsr166	1.9	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
278	dl	1.1	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
279	jsr166	1.9	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
280	dl	1.1	Comparator<? super E> mc = map.comparator();
281			if (cc==mc \|\| (cc != null && cc.equals(mc))) {
282			map.addAllForTreeSet(set, PRESENT);
283			return true;
284			}
285			}
286			return super.addAll(c);
287			}
288
289			/**
290	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
291	dl	1.1	* @throws NullPointerException if <tt>fromElement</tt> or
292	jsr166	1.11	* <tt>toElement</tt> is null and this set uses natural ordering,
293			* or its comparator does not permit null elements
294			* @throws IllegalArgumentException {@inheritDoc}
295	jsr166	1.17	* @since 1.6
296	dl	1.1	*/
297	dl	1.3	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
298			return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
299	dl	1.1	}
300
301			/**
302	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
303			* @throws NullPointerException if <tt>toElement</tt> is null and
304			* this set uses natural ordering, or its comparator does
305			* not permit null elements
306			* @throws IllegalArgumentException {@inheritDoc}
307	jsr166	1.17	* @since 1.6
308	dl	1.1	*/
309	dl	1.3	public NavigableSet<E> navigableHeadSet(E toElement) {
310			return new TreeSet<E>(m.navigableHeadMap(toElement));
311	dl	1.1	}
312
313			/**
314	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
315			* @throws NullPointerException if <tt>fromElement</tt> is null and
316			* this set uses natural ordering, or its comparator does
317			* not permit null elements
318			* @throws IllegalArgumentException {@inheritDoc}
319	jsr166	1.17	* @since 1.6
320	dl	1.1	*/
321	dl	1.3	public NavigableSet<E> navigableTailSet(E fromElement) {
322			return new TreeSet<E>(m.navigableTailMap(fromElement));
323			}
324
325			/**
326	jsr166	1.11	* Equivalent to {@link #navigableSubSet} but with a return type
327			* conforming to the <tt>SortedSet</tt> interface.
328			*
329			* <p>{@inheritDoc}
330			*
331			* @throws ClassCastException {@inheritDoc}
332	dl	1.3	* @throws NullPointerException if <tt>fromElement</tt> or
333	jsr166	1.11	* <tt>toElement</tt> is null and this set uses natural ordering,
334			* or its comparator does not permit null elements
335			* @throws IllegalArgumentException {@inheritDoc}
336	dl	1.3	*/
337			public SortedSet<E> subSet(E fromElement, E toElement) {
338			return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
339			}
340
341			/**
342	jsr166	1.11	* Equivalent to {@link #navigableHeadSet} but with a return type
343			* conforming to the <tt>SortedSet</tt> interface.
344			*
345			* <p>{@inheritDoc}
346	dl	1.3	*
347	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
348			* @throws NullPointerException if <tt>toElement</tt> is null
349			* and this set uses natural ordering, or its comparator does
350			* not permit null elements
351			* @throws IllegalArgumentException {@inheritDoc}
352	dl	1.3	*/
353			public SortedSet<E> headSet(E toElement) {
354			return new TreeSet<E>(m.navigableHeadMap(toElement));
355			}
356
357			/**
358	jsr166	1.11	* Equivalent to {@link #navigableTailSet} but with a return type
359			* conforming to the <tt>SortedSet</tt> interface.
360			*
361			* <p>{@inheritDoc}
362			*
363			* @throws ClassCastException {@inheritDoc}
364			* @throws NullPointerException if <tt>fromElement</tt> is null
365			* and this set uses natural ordering, or its comparator does
366			* not permit null elements
367			* @throws IllegalArgumentException {@inheritDoc}
368	dl	1.3	*/
369			public SortedSet<E> tailSet(E fromElement) {
370			return new TreeSet<E>(m.navigableTailMap(fromElement));
371	dl	1.1	}
372
373			public Comparator<? super E> comparator() {
374			return m.comparator();
375			}
376
377			/**
378	jsr166	1.11	* @throws NoSuchElementException {@inheritDoc}
379	dl	1.1	*/
380			public E first() {
381			return m.firstKey();
382			}
383
384			/**
385	jsr166	1.11	* @throws NoSuchElementException {@inheritDoc}
386	dl	1.1	*/
387			public E last() {
388			return m.lastKey();
389			}
390
391			// NavigableSet API methods
392
393			/**
394	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
395	jsr166	1.15	* @throws NullPointerException if the specified element is null
396			* and this set uses natural ordering, or its comparator
397			* does not permit null elements
398	jsr166	1.17	* @since 1.6
399	dl	1.1	*/
400	jsr166	1.11	public E lower(E e) {
401			return m.lowerKey(e);
402	dl	1.1	}
403
404			/**
405	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
406	jsr166	1.15	* @throws NullPointerException if the specified element is null
407			* and this set uses natural ordering, or its comparator
408			* does not permit null elements
409	jsr166	1.17	* @since 1.6
410	dl	1.1	*/
411	jsr166	1.11	public E floor(E e) {
412			return m.floorKey(e);
413	dl	1.1	}
414
415			/**
416	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
417	jsr166	1.15	* @throws NullPointerException if the specified element is null
418			* and this set uses natural ordering, or its comparator
419			* does not permit null elements
420	jsr166	1.17	* @since 1.6
421	dl	1.1	*/
422	jsr166	1.11	public E ceiling(E e) {
423			return m.ceilingKey(e);
424	dl	1.1	}
425
426			/**
427	jsr166	1.11	* @throws ClassCastException {@inheritDoc}
428	jsr166	1.15	* @throws NullPointerException if the specified element is null
429			* and this set uses natural ordering, or its comparator
430			* does not permit null elements
431	jsr166	1.17	* @since 1.6
432	dl	1.1	*/
433	jsr166	1.7	public E higher(E e) {
434			return m.higherKey(e);
435	dl	1.1	}
436
437	jsr166	1.17	/**
438			* @since 1.6
439			*/
440	dl	1.1	public E pollFirst() {
441			Map.Entry<E,?> e = m.pollFirstEntry();
442			return (e == null)? null : e.getKey();
443			}
444
445	jsr166	1.17	/**
446			* @since 1.6
447			*/
448	dl	1.1	public E pollLast() {
449			Map.Entry<E,?> e = m.pollLastEntry();
450			return (e == null)? null : e.getKey();
451			}
452
453			/**
454			* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
455			* themselves are not cloned.)
456			*
457	jsr166	1.11	* @return a shallow copy of this set
458	dl	1.1	*/
459			public Object clone() {
460			TreeSet<E> clone = null;
461			try {
462			clone = (TreeSet<E>) super.clone();
463			} catch (CloneNotSupportedException e) {
464			throw new InternalError();
465			}
466
467			clone.m = new TreeMap<E,Object>(m);
468
469			return clone;
470			}
471
472			/**
473			* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
474			* serialize it).
475			*
476			* @serialData Emits the comparator used to order this set, or
477	jsr166	1.11	* <tt>null</tt> if it obeys its elements' natural ordering
478			* (Object), followed by the size of the set (the number of
479			* elements it contains) (int), followed by all of its
480			* elements (each an Object) in order (as determined by the
481			* set's Comparator, or by the elements' natural ordering if
482	dl	1.1	* the set has no Comparator).
483			*/
484			private void writeObject(java.io.ObjectOutputStream s)
485			throws java.io.IOException {
486			// Write out any hidden stuff
487			s.defaultWriteObject();
488
489			// Write out Comparator
490			s.writeObject(m.comparator());
491
492			// Write out size
493			s.writeInt(m.size());
494
495			// Write out all elements in the proper order.
496			for (Iterator i=m.keySet().iterator(); i.hasNext(); )
497			s.writeObject(i.next());
498			}
499
500			/**
501			* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
502			* deserialize it).
503			*/
504			private void readObject(java.io.ObjectInputStream s)
505			throws java.io.IOException, ClassNotFoundException {
506			// Read in any hidden stuff
507			s.defaultReadObject();
508
509			// Read in Comparator
510	jsr166	1.9	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
511	dl	1.1
512			// Create backing TreeMap
513			TreeMap<E,Object> tm;
514			if (c==null)
515			tm = new TreeMap<E,Object>();
516			else
517			tm = new TreeMap<E,Object>(c);
518			m = tm;
519
520			// Read in size
521			int size = s.readInt();
522
523			tm.readTreeSet(size, s, PRESENT);
524			}
525
526			private static final long serialVersionUID = -2479143000061671589L;
527			}