java/util/TreeSet.java

/*
 * %W% %E%
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;
import java.util.*; // for javadoc (till 6280605 is fixed)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    // NavigableSet API methods

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

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

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

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

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

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

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

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

        return clone;
    }

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

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

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

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

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

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

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

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

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

    private static final long serialVersionUID = -2479143000061671589L;
}
Revision:	1.18
Committed:	Mon Jul 18 01:14:34 2005 UTC (18 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.17:	+10 -10 lines
Log Message:	doc fixes
#	Content
1	/*
2	* %W% %E%
3	*
4	* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	*/
7
8	package java.util;
9	import java.util.*; // for javadoc (till 6280605 is fixed)
10
11	/**
12	* A {@link NavigableSet} implementation based on a {@link TreeMap}.
13	* The elements are ordered using their {@linkplain Comparable natural
14	* ordering}, or by a {@link Comparator} provided at set creation
15	* time, depending on which constructor is used.
16	*
17	* <p>This implementation provides guaranteed log(n) time cost for the basic
18	* operations (<tt>add</tt>, <tt>remove</tt> and <tt>contains</tt>).
19	*
20	* <p>Note that the ordering maintained by a set (whether or not an explicit
21	* comparator is provided) must be <i>consistent with equals</i> if it is to
22	* correctly implement the <tt>Set</tt> interface. (See <tt>Comparable</tt>
23	* or <tt>Comparator</tt> for a precise definition of <i>consistent with
24	* equals</i>.) This is so because the <tt>Set</tt> interface is defined in
25	* terms of the <tt>equals</tt> operation, but a <tt>TreeSet</tt> instance
26	* performs all element comparisons using its <tt>compareTo</tt> (or
27	* <tt>compare</tt>) method, so two elements that are deemed equal by this method
28	* are, from the standpoint of the set, equal. The behavior of a set
29	* <i>is</i> well-defined even if its ordering is inconsistent with equals; it
30	* just fails to obey the general contract of the <tt>Set</tt> interface.
31	*
32	* <p><strong>Note that this implementation is not synchronized.</strong>
33	* If multiple threads access a tree set concurrently, and at least one
34	* of the threads modifies the set, it <i>must</i> be synchronized
35	* externally. This is typically accomplished by synchronizing on some
36	* object that naturally encapsulates the set.
37	* If no such object exists, the set should be "wrapped" using the
38	* {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
39	* method. This is best done at creation time, to prevent accidental
40	* unsynchronized access to the set: <pre>
41	* SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
42	*
43	* <p>The iterators returned by this class's <tt>iterator</tt> method are
44	* <i>fail-fast</i>: if the set is modified at any time after the iterator is
45	* created, in any way except through the iterator's own <tt>remove</tt>
46	* method, the iterator will throw a {@link ConcurrentModificationException}.
47	* Thus, in the face of concurrent modification, the iterator fails quickly
48	* and cleanly, rather than risking arbitrary, non-deterministic behavior at
49	* an undetermined time in the future.
50	*
51	* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
52	* as it is, generally speaking, impossible to make any hard guarantees in the
53	* presence of unsynchronized concurrent modification. Fail-fast iterators
54	* throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
55	* Therefore, it would be wrong to write a program that depended on this
56	* exception for its correctness: <i>the fail-fast behavior of iterators
57	* should be used only to detect bugs.</i>
58	*
59	* <p>This class is a member of the
60	* <a href="{@docRoot}/../guide/collections/index.html">
61	* Java Collections Framework</a>.
62	*
63	* @param <E> the type of elements maintained by this set
64	*
65	* @author Josh Bloch
66	* @version %I%, %G%
67	* @see Collection
68	* @see Set
69	* @see HashSet
70	* @see Comparable
71	* @see Comparator
72	* @see TreeMap
73	* @since 1.2
74	*/
75
76	public class TreeSet<E>
77	extends AbstractSet<E>
78	implements NavigableSet<E>, Cloneable, java.io.Serializable
79	{
80	private transient NavigableMap<E,Object> m; // The backing Map
81
82	// Dummy value to associate with an Object in the backing Map
83	private static final Object PRESENT = new Object();
84
85	/**
86	* Constructs a set backed by the specified navigable map.
87	*/
88	private TreeSet(NavigableMap<E,Object> m) {
89	this.m = m;
90	}
91
92	/**
93	* Constructs a new, empty tree set, sorted according to the
94	* natural ordering of its elements. All elements inserted into
95	* the set must implement the {@link Comparable} interface.
96	* Furthermore, all such elements must be <i>mutually
97	* comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
98	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
99	* <tt>e2</tt> in the set. If the user attempts to add an element
100	* to the set that violates this constraint (for example, the user
101	* attempts to add a string element to a set whose elements are
102	* integers), the <tt>add(Object)</tt> call will throw a
103	* <tt>ClassCastException</tt>.
104	*/
105	public TreeSet() {
106	this(new TreeMap<E,Object>());
107	}
108
109	/**
110	* Constructs a new, empty tree set, sorted according to the specified
111	* comparator. All elements inserted into the set must be <i>mutually
112	* comparable</i> by the specified comparator: <tt>comparator.compare(e1,
113	* e2)</tt> must not throw a <tt>ClassCastException</tt> for any elements
114	* <tt>e1</tt> and <tt>e2</tt> in the set. If the user attempts to add
115	* an element to the set that violates this constraint, the
116	* <tt>add(Object)</tt> call will throw a <tt>ClassCastException</tt>.
117	*
118	* @param comparator the comparator that will be used to order this set.
119	* If <tt>null</tt>, the {@linkplain Comparable natural
120	* ordering} of the elements will be used.
121	*/
122	public TreeSet(Comparator<? super E> comparator) {
123	this(new TreeMap<E,Object>(comparator));
124	}
125
126	/**
127	* Constructs a new tree set containing the elements in the specified
128	* collection, sorted according to the <i>natural ordering</i> of its
129	* elements. All elements inserted into the set must implement the
130	* {@link Comparable} interface. Furthermore, all such elements must be
131	* <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt> must not throw a
132	* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and
133	* <tt>e2</tt> in the set.
134	*
135	* @param c collection whose elements will comprise the new set
136	* @throws ClassCastException if the elements in <tt>c</tt> are
137	* not {@link Comparable}, or are not mutually comparable
138	* @throws NullPointerException if the specified collection is null
139	*/
140	public TreeSet(Collection<? extends E> c) {
141	this();
142	addAll(c);
143	}
144
145	/**
146	* Constructs a new tree set containing the same elements and
147	* using the same ordering as the specified sorted set.
148	*
149	* @param s sorted set whose elements will comprise the new set
150	* @throws NullPointerException if the specified sorted set is null
151	*/
152	public TreeSet(SortedSet<E> s) {
153	this(s.comparator());
154	addAll(s);
155	}
156
157	/**
158	* Returns an iterator over the elements in this set in ascending order.
159	*
160	* @return an iterator over the elements in this set in ascending order
161	*/
162	public Iterator<E> iterator() {
163	return m.keySet().iterator();
164	}
165
166	/**
167	* Returns an iterator over the elements in this set in descending order.
168	*
169	* @return an iterator over the elements in this set in descending order
170	* @since 1.6
171	*/
172	public Iterator<E> descendingIterator() {
173	return m.descendingKeySet().iterator();
174	}
175
176	/**
177	* Returns the number of elements in this set (its cardinality).
178	*
179	* @return the number of elements in this set (its cardinality)
180	*/
181	public int size() {
182	return m.size();
183	}
184
185	/**
186	* Returns <tt>true</tt> if this set contains no elements.
187	*
188	* @return <tt>true</tt> if this set contains no elements
189	*/
190	public boolean isEmpty() {
191	return m.isEmpty();
192	}
193
194	/**
195	* Returns <tt>true</tt> if this set contains the specified element.
196	* More formally, returns <tt>true</tt> if and only if this set
197	* contains an element <tt>e</tt> such that
198	* <tt>(o==null ? e==null : o.equals(e))</tt>.
199	*
200	* @param o object to be checked for containment in this set
201	* @return <tt>true</tt> if this set contains the specified element
202	* @throws ClassCastException if the specified object cannot be compared
203	* with the elements currently in the set
204	* @throws NullPointerException if the specified element is null
205	* and this set uses natural ordering, or its comparator
206	* does not permit null elements
207	*/
208	public boolean contains(Object o) {
209	return m.containsKey(o);
210	}
211
212	/**
213	* Adds the specified element to this set if it is not already present.
214	* More formally, adds the specified element <tt>e</tt> to this set if
215	* the set contains no element <tt>e2</tt> such that
216	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
217	* If this set already contains the element, the call leaves the set
218	* unchanged and returns <tt>false</tt>.
219	*
220	* @param e element to be added to this set
221	* @return <tt>true</tt> if this set did not already contain the specified
222	* element
223	* @throws ClassCastException if the specified object cannot be compared
224	* with the elements currently in this set
225	* @throws NullPointerException if the specified element is null
226	* and this set uses natural ordering, or its comparator
227	* does not permit null elements
228	*/
229	public boolean add(E e) {
230	return m.put(e, PRESENT)==null;
231	}
232
233	/**
234	* Removes the specified element from this set if it is present.
235	* More formally, removes an element <tt>e</tt> such that
236	* <tt>(o==null ? e==null : o.equals(e))</tt>,
237	* if this set contains such an element. Returns <tt>true</tt> if
238	* this set contained the element (or equivalently, if this set
239	* changed as a result of the call). (This set will not contain the
240	* element once the call returns.)
241	*
242	* @param o object to be removed from this set, if present
243	* @return <tt>true</tt> if this set contained the specified element
244	* @throws ClassCastException if the specified object cannot be compared
245	* with the elements currently in this set
246	* @throws NullPointerException if the specified element is null
247	* and this set uses natural ordering, or its comparator
248	* does not permit null elements
249	*/
250	public boolean remove(Object o) {
251	return m.remove(o)==PRESENT;
252	}
253
254	/**
255	* Removes all of the elements from this set.
256	* The set will be empty after this call returns.
257	*/
258	public void clear() {
259	m.clear();
260	}
261
262	/**
263	* Adds all of the elements in the specified collection to this set.
264	*
265	* @param c collection containing elements to be added to this set
266	* @return <tt>true</tt> if this set changed as a result of the call
267	* @throws ClassCastException if the elements provided cannot be compared
268	* with the elements currently in the set
269	* @throws NullPointerException if the specified collection is null or
270	* if any element is null and this set uses natural ordering, or
271	* its comparator does not permit null elements
272	*/
273	public boolean addAll(Collection<? extends E> c) {
274	// Use linear-time version if applicable
275	if (m.size()==0 && c.size() > 0 &&
276	c instanceof SortedSet &&
277	m instanceof TreeMap) {
278	SortedSet<? extends E> set = (SortedSet<? extends E>) c;
279	TreeMap<E,Object> map = (TreeMap<E, Object>) m;
280	Comparator<? super E> cc = (Comparator<? super E>) set.comparator();
281	Comparator<? super E> mc = map.comparator();
282	if (cc==mc \|\| (cc != null && cc.equals(mc))) {
283	map.addAllForTreeSet(set, PRESENT);
284	return true;
285	}
286	}
287	return super.addAll(c);
288	}
289
290	/**
291	* @throws ClassCastException {@inheritDoc}
292	* @throws NullPointerException if <tt>fromElement</tt> or
293	* <tt>toElement</tt> is null and this set uses natural ordering,
294	* or its comparator does not permit null elements
295	* @throws IllegalArgumentException {@inheritDoc}
296	* @since 1.6
297	*/
298	public NavigableSet<E> navigableSubSet(E fromElement, E toElement) {
299	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
300	}
301
302	/**
303	* @throws ClassCastException {@inheritDoc}
304	* @throws NullPointerException if <tt>toElement</tt> is null and
305	* this set uses natural ordering, or its comparator does
306	* not permit null elements
307	* @throws IllegalArgumentException {@inheritDoc}
308	* @since 1.6
309	*/
310	public NavigableSet<E> navigableHeadSet(E toElement) {
311	return new TreeSet<E>(m.navigableHeadMap(toElement));
312	}
313
314	/**
315	* @throws ClassCastException {@inheritDoc}
316	* @throws NullPointerException if <tt>fromElement</tt> is null and
317	* this set uses natural ordering, or its comparator does
318	* not permit null elements
319	* @throws IllegalArgumentException {@inheritDoc}
320	* @since 1.6
321	*/
322	public NavigableSet<E> navigableTailSet(E fromElement) {
323	return new TreeSet<E>(m.navigableTailMap(fromElement));
324	}
325
326	/**
327	* Equivalent to {@link #navigableSubSet} but with a return type
328	* conforming to the <tt>SortedSet</tt> interface.
329	*
330	* <p>{@inheritDoc}
331	*
332	* @throws ClassCastException {@inheritDoc}
333	* @throws NullPointerException if <tt>fromElement</tt> or
334	* <tt>toElement</tt> is null and this set uses natural ordering,
335	* or its comparator does not permit null elements
336	* @throws IllegalArgumentException {@inheritDoc}
337	*/
338	public SortedSet<E> subSet(E fromElement, E toElement) {
339	return new TreeSet<E>(m.navigableSubMap(fromElement, toElement));
340	}
341
342	/**
343	* Equivalent to {@link #navigableHeadSet} but with a return type
344	* conforming to the <tt>SortedSet</tt> interface.
345	*
346	* <p>{@inheritDoc}
347	*
348	* @throws ClassCastException {@inheritDoc}
349	* @throws NullPointerException if <tt>toElement</tt> 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 new TreeSet<E>(m.navigableHeadMap(toElement));
356	}
357
358	/**
359	* Equivalent to {@link #navigableTailSet} but with a return type
360	* conforming to the <tt>SortedSet</tt> interface.
361	*
362	* <p>{@inheritDoc}
363	*
364	* @throws ClassCastException {@inheritDoc}
365	* @throws NullPointerException if <tt>fromElement</tt> is null
366	* and this set uses natural ordering, or its comparator does
367	* not permit null elements
368	* @throws IllegalArgumentException {@inheritDoc}
369	*/
370	public SortedSet<E> tailSet(E fromElement) {
371	return new TreeSet<E>(m.navigableTailMap(fromElement));
372	}
373
374	public Comparator<? super E> comparator() {
375	return m.comparator();
376	}
377
378	/**
379	* @throws NoSuchElementException {@inheritDoc}
380	*/
381	public E first() {
382	return m.firstKey();
383	}
384
385	/**
386	* @throws NoSuchElementException {@inheritDoc}
387	*/
388	public E last() {
389	return m.lastKey();
390	}
391
392	// NavigableSet API methods
393
394	/**
395	* @throws ClassCastException {@inheritDoc}
396	* @throws NullPointerException if the specified element is null
397	* and this set uses natural ordering, or its comparator
398	* does not permit null elements
399	* @since 1.6
400	*/
401	public E lower(E e) {
402	return m.lowerKey(e);
403	}
404
405	/**
406	* @throws ClassCastException {@inheritDoc}
407	* @throws NullPointerException if the specified element is null
408	* and this set uses natural ordering, or its comparator
409	* does not permit null elements
410	* @since 1.6
411	*/
412	public E floor(E e) {
413	return m.floorKey(e);
414	}
415
416	/**
417	* @throws ClassCastException {@inheritDoc}
418	* @throws NullPointerException if the specified element is null
419	* and this set uses natural ordering, or its comparator
420	* does not permit null elements
421	* @since 1.6
422	*/
423	public E ceiling(E e) {
424	return m.ceilingKey(e);
425	}
426
427	/**
428	* @throws ClassCastException {@inheritDoc}
429	* @throws NullPointerException if the specified element is null
430	* and this set uses natural ordering, or its comparator
431	* does not permit null elements
432	* @since 1.6
433	*/
434	public E higher(E e) {
435	return m.higherKey(e);
436	}
437
438	/**
439	* @since 1.6
440	*/
441	public E pollFirst() {
442	Map.Entry<E,?> e = m.pollFirstEntry();
443	return (e == null)? null : e.getKey();
444	}
445
446	/**
447	* @since 1.6
448	*/
449	public E pollLast() {
450	Map.Entry<E,?> e = m.pollLastEntry();
451	return (e == null)? null : e.getKey();
452	}
453
454	/**
455	* Returns a shallow copy of this <tt>TreeSet</tt> instance. (The elements
456	* themselves are not cloned.)
457	*
458	* @return a shallow copy of this set
459	*/
460	public Object clone() {
461	TreeSet<E> clone = null;
462	try {
463	clone = (TreeSet<E>) super.clone();
464	} catch (CloneNotSupportedException e) {
465	throw new InternalError();
466	}
467
468	clone.m = new TreeMap<E,Object>(m);
469
470	return clone;
471	}
472
473	/**
474	* Save the state of the <tt>TreeSet</tt> instance to a stream (that is,
475	* serialize it).
476	*
477	* @serialData Emits the comparator used to order this set, or
478	* <tt>null</tt> if it obeys its elements' natural ordering
479	* (Object), followed by the size of the set (the number of
480	* elements it contains) (int), followed by all of its
481	* elements (each an Object) in order (as determined by the
482	* set's Comparator, or by the elements' natural ordering if
483	* the set has no Comparator).
484	*/
485	private void writeObject(java.io.ObjectOutputStream s)
486	throws java.io.IOException {
487	// Write out any hidden stuff
488	s.defaultWriteObject();
489
490	// Write out Comparator
491	s.writeObject(m.comparator());
492
493	// Write out size
494	s.writeInt(m.size());
495
496	// Write out all elements in the proper order.
497	for (Iterator i=m.keySet().iterator(); i.hasNext(); )
498	s.writeObject(i.next());
499	}
500
501	/**
502	* Reconstitute the <tt>TreeSet</tt> instance from a stream (that is,
503	* deserialize it).
504	*/
505	private void readObject(java.io.ObjectInputStream s)
506	throws java.io.IOException, ClassNotFoundException {
507	// Read in any hidden stuff
508	s.defaultReadObject();
509
510	// Read in Comparator
511	Comparator<? super E> c = (Comparator<? super E>) s.readObject();
512
513	// Create backing TreeMap
514	TreeMap<E,Object> tm;
515	if (c==null)
516	tm = new TreeMap<E,Object>();
517	else
518	tm = new TreeMap<E,Object>(c);
519	m = tm;
520
521	// Read in size
522	int size = s.readInt();
523
524	tm.readTreeSet(size, s, PRESENT);
525	}
526
527	private static final long serialVersionUID = -2479143000061671589L;
528	}