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 ({@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}/../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
{
    /**
     * 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(Object)} 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(Object)} 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:	1.23
Committed:	Fri Apr 21 03:24:07 2006 UTC (18 years, 1 month ago) by jsr166
Branch:	MAIN
Changes since 1.22:	+3 -3 lines
Log Message:	&nbsp and @code are immiscible
#	Content
1	/*
2	* %W% %E%
3	*
4	* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	*/
7
8	package java.util;
9
10	/**
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	*
16	* <p>This implementation provides guaranteed log(n) time cost for the basic
17	* operations ({@code add}, {@code remove} and {@code contains}).
18	*
19	* <p>Note that the ordering maintained by a set (whether or not an explicit
20	* comparator is provided) must be <i>consistent with equals</i> if it is to
21	* correctly implement the {@code Set} interface. (See {@code Comparable}
22	* or {@code Comparator} for a precise definition of <i>consistent with
23	* equals</i>.) This is so because the {@code Set} interface is defined in
24	* terms of the {@code equals} operation, but a {@code TreeSet} instance
25	* performs all element comparisons using its {@code compareTo} (or
26	* {@code compare}) method, so two elements that are deemed equal by this method
27	* 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	* just fails to obey the general contract of the {@code Set} interface.
30	*
31	* <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	*
42	* <p>The iterators returned by this class's {@code iterator} method are
43	* <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 {@code remove}
45	* method, the iterator will throw a {@link ConcurrentModificationException}.
46	* 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 {@code ConcurrentModificationException} 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	* should be used only to detect bugs.</i>
57	*
58	* <p>This class is a member of the
59	* <a href="{@docRoot}/../guide/collections/index.html">
60	* Java Collections Framework</a>.
61	*
62	* @param <E> the type of elements maintained by this set
63	*
64	* @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> extends AbstractSet<E>
76	implements NavigableSet<E>, Cloneable, java.io.Serializable
77	{
78	/**
79	* The backing map.
80	*/
81	private transient NavigableMap<E,Object> m;
82
83	// Dummy value to associate with an Object in the backing Map
84	private static final Object PRESENT = new Object();
85
86	/**
87	* Constructs a set backed by the specified navigable map.
88	*/
89	TreeSet(NavigableMap<E,Object> m) {
90	this.m = m;
91	}
92
93	/**
94	* Constructs a new, empty tree set, sorted according to the
95	* natural ordering of its elements. All elements inserted into
96	* the set must implement the {@link Comparable} interface.
97	* Furthermore, all such elements must be <i>mutually
98	* comparable</i>: {@code e1.compareTo(e2)} must not throw a
99	* {@code ClassCastException} for any elements {@code e1} and
100	* {@code e2} in the set. If the user attempts to add an element
101	* to the set that violates this constraint (for example, the user
102	* attempts to add a string element to a set whose elements are
103	* integers), the {@code add(Object)} call will throw a
104	* {@code ClassCastException}.
105	*/
106	public TreeSet() {
107	this(new TreeMap<E,Object>());
108	}
109
110	/**
111	* Constructs a new, empty tree set, sorted according to the specified
112	* comparator. All elements inserted into the set must be <i>mutually
113	* comparable</i> by the specified comparator: {@code comparator.compare(e1,
114	* e2)} must not throw a {@code ClassCastException} for any elements
115	* {@code e1} and {@code e2} in the set. If the user attempts to add
116	* an element to the set that violates this constraint, the
117	* {@code add(Object)} call will throw a {@code ClassCastException}.
118	*
119	* @param comparator the comparator that will be used to order this set.
120	* If {@code null}, the {@linkplain Comparable natural
121	* ordering} of the elements will be used.
122	*/
123	public TreeSet(Comparator<? super E> comparator) {
124	this(new TreeMap<E,Object>(comparator));
125	}
126
127	/**
128	* Constructs a new tree set containing the elements in the specified
129	* collection, sorted according to the <i>natural ordering</i> of its
130	* elements. All elements inserted into the set must implement the
131	* {@link Comparable} interface. Furthermore, all such elements must be
132	* <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
133	* {@code ClassCastException} for any elements {@code e1} and
134	* {@code e2} in the set.
135	*
136	* @param c collection whose elements will comprise the new set
137	* @throws ClassCastException if the elements in {@code c} are
138	* not {@link Comparable}, or are not mutually comparable
139	* @throws NullPointerException if the specified collection is null
140	*/
141	public TreeSet(Collection<? extends E> c) {
142	this();
143	addAll(c);
144	}
145
146	/**
147	* Constructs a new tree set containing the same elements and
148	* using the same ordering as the specified sorted set.
149	*
150	* @param s sorted set whose elements will comprise the new set
151	* @throws NullPointerException if the specified sorted set is null
152	*/
153	public TreeSet(SortedSet<E> s) {
154	this(s.comparator());
155	addAll(s);
156	}
157
158	/**
159	* Returns an iterator over the elements in this set in ascending order.
160	*
161	* @return an iterator over the elements in this set in ascending order
162	*/
163	public Iterator<E> iterator() {
164	return m.navigableKeySet().iterator();
165	}
166
167	/**
168	* Returns an iterator over the elements in this set in descending order.
169	*
170	* @return an iterator over the elements in this set in descending order
171	* @since 1.6
172	*/
173	public Iterator<E> descendingIterator() {
174	return m.descendingKeySet().iterator();
175	}
176
177	/**
178	* @since 1.6
179	*/
180	public NavigableSet<E> descendingSet() {
181	return new TreeSet(m.descendingMap());
182	}
183
184	/**
185	* Returns the number of elements in this set (its cardinality).
186	*
187	* @return the number of elements in this set (its cardinality)
188	*/
189	public int size() {
190	return m.size();
191	}
192
193	/**
194	* Returns {@code true} if this set contains no elements.
195	*
196	* @return {@code true} if this set contains no elements
197	*/
198	public boolean isEmpty() {
199	return m.isEmpty();
200	}
201
202	/**
203	* Returns {@code true} if this set contains the specified element.
204	* More formally, returns {@code true} if and only if this set
205	* contains an element {@code e} such that
206	* <tt>(o==null ? e==null : o.equals(e))</tt>.
207	*
208	* @param o object to be checked for containment in this set
209	* @return {@code true} if this set contains the specified element
210	* @throws ClassCastException if the specified object cannot be compared
211	* with the elements currently in the set
212	* @throws NullPointerException if the specified element is null
213	* and this set uses natural ordering, or its comparator
214	* does not permit null elements
215	*/
216	public boolean contains(Object o) {
217	return m.containsKey(o);
218	}
219
220	/**
221	* Adds the specified element to this set if it is not already present.
222	* More formally, adds the specified element {@code e} to this set if
223	* the set contains no element {@code e2} such that
224	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
225	* If this set already contains the element, the call leaves the set
226	* unchanged and returns {@code false}.
227	*
228	* @param e element to be added to this set
229	* @return {@code true} if this set did not already contain the specified
230	* element
231	* @throws ClassCastException if the specified object cannot be compared
232	* with the elements currently in this set
233	* @throws NullPointerException if the specified element is null
234	* and this set uses natural ordering, or its comparator
235	* does not permit null elements
236	*/
237	public boolean add(E e) {
238	return m.put(e, PRESENT)==null;
239	}
240
241	/**
242	* Removes the specified element from this set if it is present.
243	* More formally, removes an element {@code e} such that
244	* <tt>(o==null ? e==null : o.equals(e))</tt>,
245	* if this set contains such an element. Returns {@code true} if
246	* this set contained the element (or equivalently, if this set
247	* changed as a result of the call). (This set will not contain the
248	* element once the call returns.)
249	*
250	* @param o object to be removed from this set, if present
251	* @return {@code true} if this set contained the specified element
252	* @throws ClassCastException if the specified object cannot be compared
253	* with the elements currently in this set
254	* @throws NullPointerException if the specified element is null
255	* and this set uses natural ordering, or its comparator
256	* does not permit null elements
257	*/
258	public boolean remove(Object o) {
259	return m.remove(o)==PRESENT;
260	}
261
262	/**
263	* Removes all of the elements from this set.
264	* The set will be empty after this call returns.
265	*/
266	public void clear() {
267	m.clear();
268	}
269
270	/**
271	* Adds all of the elements in the specified collection to this set.
272	*
273	* @param c collection containing elements to be added to this set
274	* @return {@code true} if this set changed as a result of the call
275	* @throws ClassCastException if the elements provided cannot be compared
276	* with the elements currently in the set
277	* @throws NullPointerException if the specified collection is null or
278	* if any element is null and this set uses natural ordering, or
279	* its comparator does not permit null elements
280	*/
281	public boolean addAll(Collection<? extends E> c) {
282	// Use linear-time version if applicable
283	if (m.size()==0 && c.size() > 0 &&
284	c instanceof SortedSet &&
285	m instanceof TreeMap) {
286	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
287	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
288	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
289	Comparator<? super E> mc = map.comparator();
290	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
291	map.addAllForTreeSet(set, PRESENT);
292	return true;
293	}
294	}
295	return super.addAll(c);
296	}
297
298	/**
299	* @throws ClassCastException {@inheritDoc}
300	* @throws NullPointerException if {@code fromElement} or {@code toElement}
301	* is null and this set uses natural ordering, or its comparator
302	* does not permit null elements
303	* @throws IllegalArgumentException {@inheritDoc}
304	* @since 1.6
305	*/
306	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
307	E toElement, boolean toInclusive) {
308	return new TreeSet<E>(m.subMap(fromElement, fromInclusive,
309	toElement, toInclusive));
310	}
311
312	/**
313	* @throws ClassCastException {@inheritDoc}
314	* @throws NullPointerException if {@code toElement} is null and
315	* this set uses natural ordering, or its comparator does
316	* not permit null elements
317	* @throws IllegalArgumentException {@inheritDoc}
318	* @since 1.6
319	*/
320	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
321	return new TreeSet<E>(m.headMap(toElement, inclusive));
322	}
323
324	/**
325	* @throws ClassCastException {@inheritDoc}
326	* @throws NullPointerException if {@code fromElement} is null and
327	* this set uses natural ordering, or its comparator does
328	* not permit null elements
329	* @throws IllegalArgumentException {@inheritDoc}
330	* @since 1.6
331	*/
332	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
333	return new TreeSet<E>(m.tailMap(fromElement, inclusive));
334	}
335
336	/**
337	* @throws ClassCastException {@inheritDoc}
338	* @throws NullPointerException if {@code fromElement} or
339	* {@code toElement} is null and this set uses natural ordering,
340	* or its comparator does not permit null elements
341	* @throws IllegalArgumentException {@inheritDoc}
342	*/
343	public SortedSet<E> subSet(E fromElement, E toElement) {
344	return subSet(fromElement, true, toElement, false);
345	}
346
347	/**
348	* @throws ClassCastException {@inheritDoc}
349	* @throws NullPointerException if {@code toElement} is null
350	* and this set uses natural ordering, or its comparator does
351	* not permit null elements
352	* @throws IllegalArgumentException {@inheritDoc}
353	*/
354	public SortedSet<E> headSet(E toElement) {
355	return headSet(toElement, false);
356	}
357
358	/**
359	* @throws ClassCastException {@inheritDoc}
360	* @throws NullPointerException if {@code fromElement} is null
361	* and this set uses natural ordering, or its comparator does
362	* not permit null elements
363	* @throws IllegalArgumentException {@inheritDoc}
364	*/
365	public SortedSet<E> tailSet(E fromElement) {
366	return tailSet(fromElement, true);
367	}
368
369	public Comparator<? super E> comparator() {
370	return m.comparator();
371	}
372
373	/**
374	* @throws NoSuchElementException {@inheritDoc}
375	*/
376	public E first() {
377	return m.firstKey();
378	}
379
380	/**
381	* @throws NoSuchElementException {@inheritDoc}
382	*/
383	public E last() {
384	return m.lastKey();
385	}
386
387	// NavigableSet API methods
388
389	/**
390	* @throws ClassCastException {@inheritDoc}
391	* @throws NullPointerException if the specified element is null
392	* and this set uses natural ordering, or its comparator
393	* does not permit null elements
394	* @since 1.6
395	*/
396	public E lower(E e) {
397	return m.lowerKey(e);
398	}
399
400	/**
401	* @throws ClassCastException {@inheritDoc}
402	* @throws NullPointerException if the specified element is null
403	* and this set uses natural ordering, or its comparator
404	* does not permit null elements
405	* @since 1.6
406	*/
407	public E floor(E e) {
408	return m.floorKey(e);
409	}
410
411	/**
412	* @throws ClassCastException {@inheritDoc}
413	* @throws NullPointerException if the specified element is null
414	* and this set uses natural ordering, or its comparator
415	* does not permit null elements
416	* @since 1.6
417	*/
418	public E ceiling(E e) {
419	return m.ceilingKey(e);
420	}
421
422	/**
423	* @throws ClassCastException {@inheritDoc}
424	* @throws NullPointerException if the specified element is null
425	* and this set uses natural ordering, or its comparator
426	* does not permit null elements
427	* @since 1.6
428	*/
429	public E higher(E e) {
430	return m.higherKey(e);
431	}
432
433	/**
434	* @since 1.6
435	*/
436	public E pollFirst() {
437	Map.Entry<E,?> e = m.pollFirstEntry();
438	return (e == null)? null : e.getKey();
439	}
440
441	/**
442	* @since 1.6
443	*/
444	public E pollLast() {
445	Map.Entry<E,?> e = m.pollLastEntry();
446	return (e == null)? null : e.getKey();
447	}
448
449	/**
450	* Returns a shallow copy of this {@code TreeSet} instance. (The elements
451	* themselves are not cloned.)
452	*
453	* @return a shallow copy of this set
454	*/
455	public Object clone() {
456	TreeSet<E> clone = null;
457	try {
458	clone = (TreeSet<E>) super.clone();
459	} catch (CloneNotSupportedException e) {
460	throw new InternalError();
461	}
462
463	clone.m = new TreeMap<E,Object>(m);
464	return clone;
465	}
466
467	/**
468	* Save the state of the {@code TreeSet} instance to a stream (that is,
469	* serialize it).
470	*
471	* @serialData Emits the comparator used to order this set, or
472	* {@code null} if it obeys its elements' natural ordering
473	* (Object), followed by the size of the set (the number of
474	* elements it contains) (int), followed by all of its
475	* elements (each an Object) in order (as determined by the
476	* set's Comparator, or by the elements' natural ordering if
477	* the set has no Comparator).
478	*/
479	private void writeObject(java.io.ObjectOutputStream s)
480	throws java.io.IOException {
481	// Write out any hidden stuff
482	s.defaultWriteObject();
483
484	// Write out Comparator
485	s.writeObject(m.comparator());
486
487	// Write out size
488	s.writeInt(m.size());
489
490	// Write out all elements in the proper order.
491	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
492	s.writeObject(i.next());
493	}
494
495	/**
496	* Reconstitute the {@code TreeSet} instance from a stream (that is,
497	* deserialize it).
498	*/
499	private void readObject(java.io.ObjectInputStream s)
500	throws java.io.IOException, ClassNotFoundException {
501	// Read in any hidden stuff
502	s.defaultReadObject();
503
504	// Read in Comparator
505	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
506
507	// Create backing TreeMap
508	TreeMap<E,Object> tm;
509	if (c==null)
510	tm = new TreeMap<E,Object>();
511	else
512	tm = new TreeMap<E,Object>(c);
513	m = tm;
514
515	// Read in size
516	int size = s.readInt();
517
518	tm.readTreeSet(size, s, PRESENT);
519	}
520
521	private static final long serialVersionUID = -2479143000061671589L;
522	}