java/util/TreeSet.java

/*
 * Copyright (c) 1998, 2008, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.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
 * @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<E>(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 (E e : m.keySet())
            s.writeObject(e);
    }

    /**
     * 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:	1.33
Committed:	Sat May 7 12:22:03 2011 UTC (13 years ago) by dl
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.32:	+0 -0 lines
State:	*FILE REMOVED*
Log Message:	Stop shadowing OpenJDK classes not originated by jsr166
#	Content
1	/*
2	* Copyright (c) 1998, 2008, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22	* or visit www.oracle.com if you need additional information or have any
23	* 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	* @see Collection
84	* @see Set
85	* @see HashSet
86	* @see Comparable
87	* @see Comparator
88	* @see TreeMap
89	* @since 1.2
90	*/
91
92	public class TreeSet<E> extends AbstractSet<E>
93	implements NavigableSet<E>, Cloneable, java.io.Serializable
94	{
95	/**
96	* The backing map.
97	*/
98	private transient NavigableMap<E,Object> m;
99
100	// Dummy value to associate with an Object in the backing Map
101	private static final Object PRESENT = new Object();
102
103	/**
104	* Constructs a set backed by the specified navigable map.
105	*/
106	TreeSet(NavigableMap<E,Object> m) {
107	this.m = m;
108	}
109
110	/**
111	* Constructs a new, empty tree set, sorted according to the
112	* natural ordering of its elements. All elements inserted into
113	* the set must implement the {@link Comparable} interface.
114	* Furthermore, all such elements must be <i>mutually
115	* comparable</i>: {@code e1.compareTo(e2)} must not throw a
116	* {@code ClassCastException} for any elements {@code e1} and
117	* {@code e2} in the set. If the user attempts to add an element
118	* to the set that violates this constraint (for example, the user
119	* attempts to add a string element to a set whose elements are
120	* integers), the {@code add} call will throw a
121	* {@code ClassCastException}.
122	*/
123	public TreeSet() {
124	this(new TreeMap<E,Object>());
125	}
126
127	/**
128	* Constructs a new, empty tree set, sorted according to the specified
129	* comparator. All elements inserted into the set must be <i>mutually
130	* comparable</i> by the specified comparator: {@code comparator.compare(e1,
131	* e2)} must not throw a {@code ClassCastException} for any elements
132	* {@code e1} and {@code e2} in the set. If the user attempts to add
133	* an element to the set that violates this constraint, the
134	* {@code add} call will throw a {@code ClassCastException}.
135	*
136	* @param comparator the comparator that will be used to order this set.
137	* If {@code null}, the {@linkplain Comparable natural
138	* ordering} of the elements will be used.
139	*/
140	public TreeSet(Comparator<? super E> comparator) {
141	this(new TreeMap<E,Object>(comparator));
142	}
143
144	/**
145	* Constructs a new tree set containing the elements in the specified
146	* collection, sorted according to the <i>natural ordering</i> of its
147	* elements. All elements inserted into the set must implement the
148	* {@link Comparable} interface. Furthermore, all such elements must be
149	* <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
150	* {@code ClassCastException} for any elements {@code e1} and
151	* {@code e2} in the set.
152	*
153	* @param c collection whose elements will comprise the new set
154	* @throws ClassCastException if the elements in {@code c} are
155	* not {@link Comparable}, or are not mutually comparable
156	* @throws NullPointerException if the specified collection is null
157	*/
158	public TreeSet(Collection<? extends E> c) {
159	this();
160	addAll(c);
161	}
162
163	/**
164	* Constructs a new tree set containing the same elements and
165	* using the same ordering as the specified sorted set.
166	*
167	* @param s sorted set whose elements will comprise the new set
168	* @throws NullPointerException if the specified sorted set is null
169	*/
170	public TreeSet(SortedSet<E> s) {
171	this(s.comparator());
172	addAll(s);
173	}
174
175	/**
176	* Returns an iterator over the elements in this set in ascending order.
177	*
178	* @return an iterator over the elements in this set in ascending order
179	*/
180	public Iterator<E> iterator() {
181	return m.navigableKeySet().iterator();
182	}
183
184	/**
185	* Returns an iterator over the elements in this set in descending order.
186	*
187	* @return an iterator over the elements in this set in descending order
188	* @since 1.6
189	*/
190	public Iterator<E> descendingIterator() {
191	return m.descendingKeySet().iterator();
192	}
193
194	/**
195	* @since 1.6
196	*/
197	public NavigableSet<E> descendingSet() {
198	return new TreeSet<E>(m.descendingMap());
199	}
200
201	/**
202	* Returns the number of elements in this set (its cardinality).
203	*
204	* @return the number of elements in this set (its cardinality)
205	*/
206	public int size() {
207	return m.size();
208	}
209
210	/**
211	* Returns {@code true} if this set contains no elements.
212	*
213	* @return {@code true} if this set contains no elements
214	*/
215	public boolean isEmpty() {
216	return m.isEmpty();
217	}
218
219	/**
220	* Returns {@code true} if this set contains the specified element.
221	* More formally, returns {@code true} if and only if this set
222	* contains an element {@code e} such that
223	* <tt>(o==null ? e==null : o.equals(e))</tt>.
224	*
225	* @param o object to be checked for containment in this set
226	* @return {@code true} if this set contains the specified element
227	* @throws ClassCastException if the specified object cannot be compared
228	* with the elements currently in the set
229	* @throws NullPointerException if the specified element is null
230	* and this set uses natural ordering, or its comparator
231	* does not permit null elements
232	*/
233	public boolean contains(Object o) {
234	return m.containsKey(o);
235	}
236
237	/**
238	* Adds the specified element to this set if it is not already present.
239	* More formally, adds the specified element {@code e} to this set if
240	* the set contains no element {@code e2} such that
241	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
242	* If this set already contains the element, the call leaves the set
243	* unchanged and returns {@code false}.
244	*
245	* @param e element to be added to this set
246	* @return {@code true} if this set did not already contain the specified
247	* element
248	* @throws ClassCastException if the specified object cannot be compared
249	* with the elements currently in this set
250	* @throws NullPointerException if the specified element is null
251	* and this set uses natural ordering, or its comparator
252	* does not permit null elements
253	*/
254	public boolean add(E e) {
255	return m.put(e, PRESENT)==null;
256	}
257
258	/**
259	* Removes the specified element from this set if it is present.
260	* More formally, removes an element {@code e} such that
261	* <tt>(o==null ? e==null : o.equals(e))</tt>,
262	* if this set contains such an element. Returns {@code true} if
263	* this set contained the element (or equivalently, if this set
264	* changed as a result of the call). (This set will not contain the
265	* element once the call returns.)
266	*
267	* @param o object to be removed from this set, if present
268	* @return {@code true} if this set contained the specified element
269	* @throws ClassCastException if the specified object cannot be compared
270	* with the elements currently in this set
271	* @throws NullPointerException if the specified element is null
272	* and this set uses natural ordering, or its comparator
273	* does not permit null elements
274	*/
275	public boolean remove(Object o) {
276	return m.remove(o)==PRESENT;
277	}
278
279	/**
280	* Removes all of the elements from this set.
281	* The set will be empty after this call returns.
282	*/
283	public void clear() {
284	m.clear();
285	}
286
287	/**
288	* Adds all of the elements in the specified collection to this set.
289	*
290	* @param c collection containing elements to be added to this set
291	* @return {@code true} if this set changed as a result of the call
292	* @throws ClassCastException if the elements provided cannot be compared
293	* with the elements currently in the set
294	* @throws NullPointerException if the specified collection is null or
295	* if any element is null and this set uses natural ordering, or
296	* its comparator does not permit null elements
297	*/
298	public boolean addAll(Collection<? extends E> c) {
299	// Use linear-time version if applicable
300	if (m.size()==0 && c.size() > 0 &&
301	c instanceof SortedSet &&
302	m instanceof TreeMap) {
303	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
304	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
305	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
306	Comparator<? super E> mc = map.comparator();
307	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
308	map.addAllForTreeSet(set, PRESENT);
309	return true;
310	}
311	}
312	return super.addAll(c);
313	}
314
315	/**
316	* @throws ClassCastException {@inheritDoc}
317	* @throws NullPointerException if {@code fromElement} or {@code toElement}
318	* is null and this set uses natural ordering, or its comparator
319	* does not permit null elements
320	* @throws IllegalArgumentException {@inheritDoc}
321	* @since 1.6
322	*/
323	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
324	E toElement, boolean toInclusive) {
325	return new TreeSet<E>(m.subMap(fromElement, fromInclusive,
326	toElement, toInclusive));
327	}
328
329	/**
330	* @throws ClassCastException {@inheritDoc}
331	* @throws NullPointerException if {@code toElement} is null and
332	* this set uses natural ordering, or its comparator does
333	* not permit null elements
334	* @throws IllegalArgumentException {@inheritDoc}
335	* @since 1.6
336	*/
337	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
338	return new TreeSet<E>(m.headMap(toElement, inclusive));
339	}
340
341	/**
342	* @throws ClassCastException {@inheritDoc}
343	* @throws NullPointerException if {@code fromElement} is null and
344	* this set uses natural ordering, or its comparator does
345	* not permit null elements
346	* @throws IllegalArgumentException {@inheritDoc}
347	* @since 1.6
348	*/
349	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
350	return new TreeSet<E>(m.tailMap(fromElement, inclusive));
351	}
352
353	/**
354	* @throws ClassCastException {@inheritDoc}
355	* @throws NullPointerException if {@code fromElement} or
356	* {@code toElement} is null and this set uses natural ordering,
357	* or its comparator does not permit null elements
358	* @throws IllegalArgumentException {@inheritDoc}
359	*/
360	public SortedSet<E> subSet(E fromElement, E toElement) {
361	return subSet(fromElement, true, toElement, false);
362	}
363
364	/**
365	* @throws ClassCastException {@inheritDoc}
366	* @throws NullPointerException if {@code toElement} is null
367	* and this set uses natural ordering, or its comparator does
368	* not permit null elements
369	* @throws IllegalArgumentException {@inheritDoc}
370	*/
371	public SortedSet<E> headSet(E toElement) {
372	return headSet(toElement, false);
373	}
374
375	/**
376	* @throws ClassCastException {@inheritDoc}
377	* @throws NullPointerException if {@code fromElement} is null
378	* and this set uses natural ordering, or its comparator does
379	* not permit null elements
380	* @throws IllegalArgumentException {@inheritDoc}
381	*/
382	public SortedSet<E> tailSet(E fromElement) {
383	return tailSet(fromElement, true);
384	}
385
386	public Comparator<? super E> comparator() {
387	return m.comparator();
388	}
389
390	/**
391	* @throws NoSuchElementException {@inheritDoc}
392	*/
393	public E first() {
394	return m.firstKey();
395	}
396
397	/**
398	* @throws NoSuchElementException {@inheritDoc}
399	*/
400	public E last() {
401	return m.lastKey();
402	}
403
404	// NavigableSet API methods
405
406	/**
407	* @throws ClassCastException {@inheritDoc}
408	* @throws NullPointerException if the specified element is null
409	* and this set uses natural ordering, or its comparator
410	* does not permit null elements
411	* @since 1.6
412	*/
413	public E lower(E e) {
414	return m.lowerKey(e);
415	}
416
417	/**
418	* @throws ClassCastException {@inheritDoc}
419	* @throws NullPointerException if the specified element is null
420	* and this set uses natural ordering, or its comparator
421	* does not permit null elements
422	* @since 1.6
423	*/
424	public E floor(E e) {
425	return m.floorKey(e);
426	}
427
428	/**
429	* @throws ClassCastException {@inheritDoc}
430	* @throws NullPointerException if the specified element is null
431	* and this set uses natural ordering, or its comparator
432	* does not permit null elements
433	* @since 1.6
434	*/
435	public E ceiling(E e) {
436	return m.ceilingKey(e);
437	}
438
439	/**
440	* @throws ClassCastException {@inheritDoc}
441	* @throws NullPointerException if the specified element is null
442	* and this set uses natural ordering, or its comparator
443	* does not permit null elements
444	* @since 1.6
445	*/
446	public E higher(E e) {
447	return m.higherKey(e);
448	}
449
450	/**
451	* @since 1.6
452	*/
453	public E pollFirst() {
454	Map.Entry<E,?> e = m.pollFirstEntry();
455	return (e == null) ? null : e.getKey();
456	}
457
458	/**
459	* @since 1.6
460	*/
461	public E pollLast() {
462	Map.Entry<E,?> e = m.pollLastEntry();
463	return (e == null) ? null : e.getKey();
464	}
465
466	/**
467	* Returns a shallow copy of this {@code TreeSet} instance. (The elements
468	* themselves are not cloned.)
469	*
470	* @return a shallow copy of this set
471	*/
472	public Object clone() {
473	TreeSet<E> clone = null;
474	try {
475	clone = (TreeSet<E>) super.clone();
476	} catch (CloneNotSupportedException e) {
477	throw new InternalError();
478	}
479
480	clone.m = new TreeMap<E,Object>(m);
481	return clone;
482	}
483
484	/**
485	* Save the state of the {@code TreeSet} instance to a stream (that is,
486	* serialize it).
487	*
488	* @serialData Emits the comparator used to order this set, or
489	* {@code null} if it obeys its elements' natural ordering
490	* (Object), followed by the size of the set (the number of
491	* elements it contains) (int), followed by all of its
492	* elements (each an Object) in order (as determined by the
493	* set's Comparator, or by the elements' natural ordering if
494	* the set has no Comparator).
495	*/
496	private void writeObject(java.io.ObjectOutputStream s)
497	throws java.io.IOException {
498	// Write out any hidden stuff
499	s.defaultWriteObject();
500
501	// Write out Comparator
502	s.writeObject(m.comparator());
503
504	// Write out size
505	s.writeInt(m.size());
506
507	// Write out all elements in the proper order.
508	for (E e : m.keySet())
509	s.writeObject(e);
510	}
511
512	/**
513	* Reconstitute the {@code TreeSet} instance from a stream (that is,
514	* deserialize it).
515	*/
516	private void readObject(java.io.ObjectInputStream s)
517	throws java.io.IOException, ClassNotFoundException {
518	// Read in any hidden stuff
519	s.defaultReadObject();
520
521	// Read in Comparator
522	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
523
524	// Create backing TreeMap
525	TreeMap<E,Object> tm;
526	if (c==null)
527	tm = new TreeMap<E,Object>();
528	else
529	tm = new TreeMap<E,Object>(c);
530	m = tm;
531
532	// Read in size
533	int size = s.readInt();
534
535	tm.readTreeSet(size, s, PRESENT);
536	}
537
538	private static final long serialVersionUID = -2479143000061671589L;
539	}