java/util/TreeSet.java

/*
 * Copyright 1998-2006 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

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 ({@code add}, {@code remove} and {@code contains}).
 *
 * <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 {@code Set} interface.  (See {@code Comparable}
 * or {@code Comparator} for a precise definition of <i>consistent with
 * equals</i>.)  This is so because the {@code Set} interface is defined in
 * terms of the {@code equals} operation, but a {@code TreeSet} instance
 * performs all element comparisons using its {@code compareTo} (or
 * {@code compare}) 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 {@code Set} 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 {@code iterator} 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 {@code remove}
 * 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 {@code ConcurrentModificationException} 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}/../technotes/guides/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
{
    /**
     * The backing map.
     */
    private transient NavigableMap<E,Object> m;

    // 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.
     */
    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>: {@code e1.compareTo(e2)} must not throw a
     * {@code ClassCastException} for any elements {@code e1} and
     * {@code e2} 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 {@code add} call will throw a
     * {@code ClassCastException}.
     */
    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: {@code comparator.compare(e1,
     * e2)} must not throw a {@code ClassCastException} for any elements
     * {@code e1} and {@code e2} in the set.  If the user attempts to add
     * an element to the set that violates this constraint, the
     * {@code add} call will throw a {@code ClassCastException}.
     *
     * @param comparator the comparator that will be used to order this set.
     *        If {@code null}, 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>: {@code e1.compareTo(e2)} must not throw a
     * {@code ClassCastException} for any elements {@code e1} and
     * {@code e2} in the set.
     *
     * @param c collection whose elements will comprise the new set
     * @throws ClassCastException if the elements in {@code c} 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.navigableKeySet().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();
    }

    /**
     * @since 1.6
     */
    public NavigableSet<E> descendingSet() {
        return new TreeSet(m.descendingMap());
    }

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

    /**
     * Returns {@code true} if this set contains the specified element.
     * More formally, returns {@code true} if and only if this set
     * contains an element {@code e} 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 {@code true} 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 {@code e} to this set if
     * the set contains no element {@code e2} 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 {@code false}.
     *
     * @param e element to be added to this set
     * @return {@code true} 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 {@code e} such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
     * if this set contains such an element.  Returns {@code true} 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 {@code true} 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 {@code true} 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 {@code fromElement} or {@code toElement}
     *         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> subSet(E fromElement, boolean fromInclusive,
                                  E toElement,   boolean toInclusive) {
        return new TreeSet<E>(m.subMap(fromElement, fromInclusive,
                                       toElement,   toInclusive));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code toElement} 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> headSet(E toElement, boolean inclusive) {
        return new TreeSet<E>(m.headMap(toElement, inclusive));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} 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> tailSet(E fromElement, boolean inclusive) {
        return new TreeSet<E>(m.tailMap(fromElement, inclusive));
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} or
     *         {@code toElement} 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 subSet(fromElement, true, toElement, false);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code toElement} 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 headSet(toElement, false);
    }

    /**
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if {@code fromElement} 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 tailSet(fromElement, true);
    }

    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 {@code TreeSet} 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 {@code TreeSet} instance to a stream (that is,
     * serialize it).
     *
     * @serialData Emits the comparator used to order this set, or
     *             {@code null} 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 {@code TreeSet} 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:	1.27
Committed:	Sun May 18 23:47:56 2008 UTC (16 years ago) by jsr166
Branch:	MAIN
Changes since 1.26:	+39 -39 lines
Log Message:	Sync with OpenJDK; untabify
#	Content
1	/*
2	* Copyright 1998-2006 Sun Microsystems, Inc. All Rights Reserved.
3	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	*
5	* This code is free software; you can redistribute it and/or modify it
6	* under the terms of the GNU General Public License version 2 only, as
7	* published by the Free Software Foundation. Sun designates this
8	* particular file as subject to the "Classpath" exception as provided
9	* by Sun in the LICENSE file that accompanied this code.
10	*
11	* This code is distributed in the hope that it will be useful, but WITHOUT
12	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14	* version 2 for more details (a copy is included in the LICENSE file that
15	* accompanied this code).
16	*
17	* You should have received a copy of the GNU General Public License version
18	* 2 along with this work; if not, write to the Free Software Foundation,
19	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20	*
21	* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22	* CA 95054 USA or visit www.sun.com if you need additional information or
23	* have any questions.
24	*/
25
26	package java.util;
27
28	/**
29	* A {@link NavigableSet} implementation based on a {@link TreeMap}.
30	* The elements are ordered using their {@linkplain Comparable natural
31	* ordering}, or by a {@link Comparator} provided at set creation
32	* time, depending on which constructor is used.
33	*
34	* <p>This implementation provides guaranteed log(n) time cost for the basic
35	* operations ({@code add}, {@code remove} and {@code contains}).
36	*
37	* <p>Note that the ordering maintained by a set (whether or not an explicit
38	* comparator is provided) must be <i>consistent with equals</i> if it is to
39	* correctly implement the {@code Set} interface. (See {@code Comparable}
40	* or {@code Comparator} for a precise definition of <i>consistent with
41	* equals</i>.) This is so because the {@code Set} interface is defined in
42	* terms of the {@code equals} operation, but a {@code TreeSet} instance
43	* performs all element comparisons using its {@code compareTo} (or
44	* {@code compare}) method, so two elements that are deemed equal by this method
45	* are, from the standpoint of the set, equal. The behavior of a set
46	* <i>is</i> well-defined even if its ordering is inconsistent with equals; it
47	* just fails to obey the general contract of the {@code Set} interface.
48	*
49	* <p><strong>Note that this implementation is not synchronized.</strong>
50	* If multiple threads access a tree set concurrently, and at least one
51	* of the threads modifies the set, it <i>must</i> be synchronized
52	* externally. This is typically accomplished by synchronizing on some
53	* object that naturally encapsulates the set.
54	* If no such object exists, the set should be "wrapped" using the
55	* {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
56	* method. This is best done at creation time, to prevent accidental
57	* unsynchronized access to the set: <pre>
58	* SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
59	*
60	* <p>The iterators returned by this class's {@code iterator} method are
61	* <i>fail-fast</i>: if the set is modified at any time after the iterator is
62	* created, in any way except through the iterator's own {@code remove}
63	* method, the iterator will throw a {@link ConcurrentModificationException}.
64	* Thus, in the face of concurrent modification, the iterator fails quickly
65	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
66	* an undetermined time in the future.
67	*
68	* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
69	* as it is, generally speaking, impossible to make any hard guarantees in the
70	* presence of unsynchronized concurrent modification. Fail-fast iterators
71	* throw {@code ConcurrentModificationException} on a best-effort basis.
72	* Therefore, it would be wrong to write a program that depended on this
73	* exception for its correctness: <i>the fail-fast behavior of iterators
74	* should be used only to detect bugs.</i>
75	*
76	* <p>This class is a member of the
77	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
78	* Java Collections Framework</a>.
79	*
80	* @param <E> the type of elements maintained by this set
81	*
82	* @author Josh Bloch
83	* @version %I%, %G%
84	* @see Collection
85	* @see Set
86	* @see HashSet
87	* @see Comparable
88	* @see Comparator
89	* @see TreeMap
90	* @since 1.2
91	*/
92
93	public class TreeSet<E> extends AbstractSet<E>
94	implements NavigableSet<E>, Cloneable, java.io.Serializable
95	{
96	/**
97	* The backing map.
98	*/
99	private transient NavigableMap<E,Object> m;
100
101	// Dummy value to associate with an Object in the backing Map
102	private static final Object PRESENT = new Object();
103
104	/**
105	* Constructs a set backed by the specified navigable map.
106	*/
107	TreeSet(NavigableMap<E,Object> m) {
108	this.m = m;
109	}
110
111	/**
112	* Constructs a new, empty tree set, sorted according to the
113	* natural ordering of its elements. All elements inserted into
114	* the set must implement the {@link Comparable} interface.
115	* Furthermore, all such elements must be <i>mutually
116	* comparable</i>: {@code e1.compareTo(e2)} must not throw a
117	* {@code ClassCastException} for any elements {@code e1} and
118	* {@code e2} in the set. If the user attempts to add an element
119	* to the set that violates this constraint (for example, the user
120	* attempts to add a string element to a set whose elements are
121	* integers), the {@code add} call will throw a
122	* {@code ClassCastException}.
123	*/
124	public TreeSet() {
125	this(new TreeMap<E,Object>());
126	}
127
128	/**
129	* Constructs a new, empty tree set, sorted according to the specified
130	* comparator. All elements inserted into the set must be <i>mutually
131	* comparable</i> by the specified comparator: {@code comparator.compare(e1,
132	* e2)} must not throw a {@code ClassCastException} for any elements
133	* {@code e1} and {@code e2} in the set. If the user attempts to add
134	* an element to the set that violates this constraint, the
135	* {@code add} call will throw a {@code ClassCastException}.
136	*
137	* @param comparator the comparator that will be used to order this set.
138	* If {@code null}, the {@linkplain Comparable natural
139	* ordering} of the elements will be used.
140	*/
141	public TreeSet(Comparator<? super E> comparator) {
142	this(new TreeMap<E,Object>(comparator));
143	}
144
145	/**
146	* Constructs a new tree set containing the elements in the specified
147	* collection, sorted according to the <i>natural ordering</i> of its
148	* elements. All elements inserted into the set must implement the
149	* {@link Comparable} interface. Furthermore, all such elements must be
150	* <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
151	* {@code ClassCastException} for any elements {@code e1} and
152	* {@code e2} in the set.
153	*
154	* @param c collection whose elements will comprise the new set
155	* @throws ClassCastException if the elements in {@code c} are
156	* not {@link Comparable}, or are not mutually comparable
157	* @throws NullPointerException if the specified collection is null
158	*/
159	public TreeSet(Collection<? extends E> c) {
160	this();
161	addAll(c);
162	}
163
164	/**
165	* Constructs a new tree set containing the same elements and
166	* using the same ordering as the specified sorted set.
167	*
168	* @param s sorted set whose elements will comprise the new set
169	* @throws NullPointerException if the specified sorted set is null
170	*/
171	public TreeSet(SortedSet<E> s) {
172	this(s.comparator());
173	addAll(s);
174	}
175
176	/**
177	* Returns an iterator over the elements in this set in ascending order.
178	*
179	* @return an iterator over the elements in this set in ascending order
180	*/
181	public Iterator<E> iterator() {
182	return m.navigableKeySet().iterator();
183	}
184
185	/**
186	* Returns an iterator over the elements in this set in descending order.
187	*
188	* @return an iterator over the elements in this set in descending order
189	* @since 1.6
190	*/
191	public Iterator<E> descendingIterator() {
192	return m.descendingKeySet().iterator();
193	}
194
195	/**
196	* @since 1.6
197	*/
198	public NavigableSet<E> descendingSet() {
199	return new TreeSet(m.descendingMap());
200	}
201
202	/**
203	* Returns the number of elements in this set (its cardinality).
204	*
205	* @return the number of elements in this set (its cardinality)
206	*/
207	public int size() {
208	return m.size();
209	}
210
211	/**
212	* Returns {@code true} if this set contains no elements.
213	*
214	* @return {@code true} if this set contains no elements
215	*/
216	public boolean isEmpty() {
217	return m.isEmpty();
218	}
219
220	/**
221	* Returns {@code true} if this set contains the specified element.
222	* More formally, returns {@code true} if and only if this set
223	* contains an element {@code e} such that
224	* <tt>(o==null ? e==null : o.equals(e))</tt>.
225	*
226	* @param o object to be checked for containment in this set
227	* @return {@code true} if this set contains the specified element
228	* @throws ClassCastException if the specified object cannot be compared
229	* with the elements currently in the set
230	* @throws NullPointerException if the specified element is null
231	* and this set uses natural ordering, or its comparator
232	* does not permit null elements
233	*/
234	public boolean contains(Object o) {
235	return m.containsKey(o);
236	}
237
238	/**
239	* Adds the specified element to this set if it is not already present.
240	* More formally, adds the specified element {@code e} to this set if
241	* the set contains no element {@code e2} such that
242	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
243	* If this set already contains the element, the call leaves the set
244	* unchanged and returns {@code false}.
245	*
246	* @param e element to be added to this set
247	* @return {@code true} if this set did not already contain the specified
248	* element
249	* @throws ClassCastException if the specified object cannot be compared
250	* with the elements currently in this set
251	* @throws NullPointerException if the specified element is null
252	* and this set uses natural ordering, or its comparator
253	* does not permit null elements
254	*/
255	public boolean add(E e) {
256	return m.put(e, PRESENT)==null;
257	}
258
259	/**
260	* Removes the specified element from this set if it is present.
261	* More formally, removes an element {@code e} such that
262	* <tt>(o==null ? e==null : o.equals(e))</tt>,
263	* if this set contains such an element. Returns {@code true} if
264	* this set contained the element (or equivalently, if this set
265	* changed as a result of the call). (This set will not contain the
266	* element once the call returns.)
267	*
268	* @param o object to be removed from this set, if present
269	* @return {@code true} if this set contained the specified element
270	* @throws ClassCastException if the specified object cannot be compared
271	* with the elements currently in this set
272	* @throws NullPointerException if the specified element is null
273	* and this set uses natural ordering, or its comparator
274	* does not permit null elements
275	*/
276	public boolean remove(Object o) {
277	return m.remove(o)==PRESENT;
278	}
279
280	/**
281	* Removes all of the elements from this set.
282	* The set will be empty after this call returns.
283	*/
284	public void clear() {
285	m.clear();
286	}
287
288	/**
289	* Adds all of the elements in the specified collection to this set.
290	*
291	* @param c collection containing elements to be added to this set
292	* @return {@code true} if this set changed as a result of the call
293	* @throws ClassCastException if the elements provided cannot be compared
294	* with the elements currently in the set
295	* @throws NullPointerException if the specified collection is null or
296	* if any element is null and this set uses natural ordering, or
297	* its comparator does not permit null elements
298	*/
299	public boolean addAll(Collection<? extends E> c) {
300	// Use linear-time version if applicable
301	if (m.size()==0 && c.size() > 0 &&
302	c instanceof SortedSet &&
303	m instanceof TreeMap) {
304	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
305	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
306	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
307	Comparator<? super E> mc = map.comparator();
308	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
309	map.addAllForTreeSet(set, PRESENT);
310	return true;
311	}
312	}
313	return super.addAll(c);
314	}
315
316	/**
317	* @throws ClassCastException {@inheritDoc}
318	* @throws NullPointerException if {@code fromElement} or {@code toElement}
319	* is null and this set uses natural ordering, or its comparator
320	* does not permit null elements
321	* @throws IllegalArgumentException {@inheritDoc}
322	* @since 1.6
323	*/
324	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
325	E toElement, boolean toInclusive) {
326	return new TreeSet<E>(m.subMap(fromElement, fromInclusive,
327	toElement, toInclusive));
328	}
329
330	/**
331	* @throws ClassCastException {@inheritDoc}
332	* @throws NullPointerException if {@code toElement} is null and
333	* this set uses natural ordering, or its comparator does
334	* not permit null elements
335	* @throws IllegalArgumentException {@inheritDoc}
336	* @since 1.6
337	*/
338	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
339	return new TreeSet<E>(m.headMap(toElement, inclusive));
340	}
341
342	/**
343	* @throws ClassCastException {@inheritDoc}
344	* @throws NullPointerException if {@code fromElement} is null and
345	* this set uses natural ordering, or its comparator does
346	* not permit null elements
347	* @throws IllegalArgumentException {@inheritDoc}
348	* @since 1.6
349	*/
350	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
351	return new TreeSet<E>(m.tailMap(fromElement, inclusive));
352	}
353
354	/**
355	* @throws ClassCastException {@inheritDoc}
356	* @throws NullPointerException if {@code fromElement} or
357	* {@code toElement} is null and this set uses natural ordering,
358	* or its comparator does not permit null elements
359	* @throws IllegalArgumentException {@inheritDoc}
360	*/
361	public SortedSet<E> subSet(E fromElement, E toElement) {
362	return subSet(fromElement, true, toElement, false);
363	}
364
365	/**
366	* @throws ClassCastException {@inheritDoc}
367	* @throws NullPointerException if {@code toElement} is null
368	* and this set uses natural ordering, or its comparator does
369	* not permit null elements
370	* @throws IllegalArgumentException {@inheritDoc}
371	*/
372	public SortedSet<E> headSet(E toElement) {
373	return headSet(toElement, false);
374	}
375
376	/**
377	* @throws ClassCastException {@inheritDoc}
378	* @throws NullPointerException if {@code fromElement} is null
379	* and this set uses natural ordering, or its comparator does
380	* not permit null elements
381	* @throws IllegalArgumentException {@inheritDoc}
382	*/
383	public SortedSet<E> tailSet(E fromElement) {
384	return tailSet(fromElement, true);
385	}
386
387	public Comparator<? super E> comparator() {
388	return m.comparator();
389	}
390
391	/**
392	* @throws NoSuchElementException {@inheritDoc}
393	*/
394	public E first() {
395	return m.firstKey();
396	}
397
398	/**
399	* @throws NoSuchElementException {@inheritDoc}
400	*/
401	public E last() {
402	return m.lastKey();
403	}
404
405	// NavigableSet API methods
406
407	/**
408	* @throws ClassCastException {@inheritDoc}
409	* @throws NullPointerException if the specified element is null
410	* and this set uses natural ordering, or its comparator
411	* does not permit null elements
412	* @since 1.6
413	*/
414	public E lower(E e) {
415	return m.lowerKey(e);
416	}
417
418	/**
419	* @throws ClassCastException {@inheritDoc}
420	* @throws NullPointerException if the specified element is null
421	* and this set uses natural ordering, or its comparator
422	* does not permit null elements
423	* @since 1.6
424	*/
425	public E floor(E e) {
426	return m.floorKey(e);
427	}
428
429	/**
430	* @throws ClassCastException {@inheritDoc}
431	* @throws NullPointerException if the specified element is null
432	* and this set uses natural ordering, or its comparator
433	* does not permit null elements
434	* @since 1.6
435	*/
436	public E ceiling(E e) {
437	return m.ceilingKey(e);
438	}
439
440	/**
441	* @throws ClassCastException {@inheritDoc}
442	* @throws NullPointerException if the specified element is null
443	* and this set uses natural ordering, or its comparator
444	* does not permit null elements
445	* @since 1.6
446	*/
447	public E higher(E e) {
448	return m.higherKey(e);
449	}
450
451	/**
452	* @since 1.6
453	*/
454	public E pollFirst() {
455	Map.Entry<E,?> e = m.pollFirstEntry();
456	return (e == null)? null : e.getKey();
457	}
458
459	/**
460	* @since 1.6
461	*/
462	public E pollLast() {
463	Map.Entry<E,?> e = m.pollLastEntry();
464	return (e == null)? null : e.getKey();
465	}
466
467	/**
468	* Returns a shallow copy of this {@code TreeSet} instance. (The elements
469	* themselves are not cloned.)
470	*
471	* @return a shallow copy of this set
472	*/
473	public Object clone() {
474	TreeSet<E> clone = null;
475	try {
476	clone = (TreeSet<E>) super.clone();
477	} catch (CloneNotSupportedException e) {
478	throw new InternalError();
479	}
480
481	clone.m = new TreeMap<E,Object>(m);
482	return clone;
483	}
484
485	/**
486	* Save the state of the {@code TreeSet} instance to a stream (that is,
487	* serialize it).
488	*
489	* @serialData Emits the comparator used to order this set, or
490	* {@code null} if it obeys its elements' natural ordering
491	* (Object), followed by the size of the set (the number of
492	* elements it contains) (int), followed by all of its
493	* elements (each an Object) in order (as determined by the
494	* set's Comparator, or by the elements' natural ordering if
495	* the set has no Comparator).
496	*/
497	private void writeObject(java.io.ObjectOutputStream s)
498	throws java.io.IOException {
499	// Write out any hidden stuff
500	s.defaultWriteObject();
501
502	// Write out Comparator
503	s.writeObject(m.comparator());
504
505	// Write out size
506	s.writeInt(m.size());
507
508	// Write out all elements in the proper order.
509	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
510	s.writeObject(i.next());
511	}
512
513	/**
514	* Reconstitute the {@code TreeSet} instance from a stream (that is,
515	* deserialize it).
516	*/
517	private void readObject(java.io.ObjectInputStream s)
518	throws java.io.IOException, ClassNotFoundException {
519	// Read in any hidden stuff
520	s.defaultReadObject();
521
522	// Read in Comparator
523	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
524
525	// Create backing TreeMap
526	TreeMap<E,Object> tm;
527	if (c==null)
528	tm = new TreeMap<E,Object>();
529	else
530	tm = new TreeMap<E,Object>(c);
531	m = tm;
532
533	// Read in size
534	int size = s.readInt();
535
536	tm.readTreeSet(size, s, PRESENT);
537	}
538
539	private static final long serialVersionUID = -2479143000061671589L;
540	}