util/concurrent/CopyOnWriteArraySet.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;
import java.util.*;

/**
 * A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
 * for all of its operations.  Thus, it shares the same basic properties:
 * <ul>
 *  <li>It is best suited for applications in which set sizes generally
 *       stay small, read-only operations
 *       vastly outnumber mutative operations, and you need
 *       to prevent interference among threads during traversal.
 *  <li>It is thread-safe.
 *  <li>Mutative operations (<tt>add</tt>, <tt>set</tt>, <tt>remove</tt>, etc.)
 *      are expensive since they usually entail copying the entire underlying
 *      array.
 *  <li>Iterators do not support the mutative <tt>remove</tt> operation.
 *  <li>Traversal via iterators is fast and cannot encounter
 *      interference from other threads. Iterators rely on
 *      unchanging snapshots of the array at the time the iterators were
 *      constructed.
 * </ul>
 *
 * <p> <b>Sample Usage.</b> The following code sketch uses a
 * copy-on-write set to maintain a set of Handler objects that
 * perform some action upon state updates.
 *
 * <pre>
 * class Handler { void handle(); ... }
 *
 * class X {
 *    private final CopyOnWriteArraySet&lt;Handler&gt; handlers
 *       = new CopyOnWriteArraySet&lt;Handler&gt;();
 *    public void addHandler(Handler h) { handlers.add(h); }
 *
 *    private long internalState;
 *    private synchronized void changeState() { internalState = ...; }
 *
 *    public void update() {
 *       changeState();
 *       for (Handler handler : handlers)
 *          handler.handle();
 *    }
 * }
 * </pre>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @see CopyOnWriteArrayList
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
        implements java.io.Serializable {
    private static final long serialVersionUID = 5457747651344034263L;

    private final CopyOnWriteArrayList<E> al;

    /**
     * Creates an empty set.
     */
    public CopyOnWriteArraySet() {
        al = new CopyOnWriteArrayList<E>();
    }

    /**
     * Creates a set containing all of the elements of the specified
     * collection.
     *
     * @param c the collection of elements to initially contain
     * @throws NullPointerException if the specified collection is null
     */
    public CopyOnWriteArraySet(Collection<? extends E> c) {
        al = new CopyOnWriteArrayList<E>();
        al.addAllAbsent(c);
    }

    /**
     * Returns the number of elements in this set.
     *
     * @return the number of elements in this set
     */
    public int size() {
        return al.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 al.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 element whose presence in this set is to be tested
     * @return <tt>true</tt> if this set contains the specified element
     */
    public boolean contains(Object o) {
        return al.contains(o);
    }

    /**
     * Returns an array containing all of the elements in this set.
     * If this set makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the
     * elements in the same order.
     *
     * <p>The returned array will be "safe" in that no references to it
     * are maintained by this set.  (In other words, this method must
     * allocate a new array even if this set is backed by an array).
     * The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all the elements in this set
     */
    public Object[] toArray() {
        return al.toArray();
    }

    /**
     * Returns an array containing all of the elements in this set; the
     * runtime type of the returned array is that of the specified array.
     * If the set fits in the specified array, it is returned therein.
     * Otherwise, a new array is allocated with the runtime type of the
     * specified array and the size of this set.
     *
     * <p>If this set fits in the specified array with room to spare
     * (i.e., the array has more elements than this set), the element in
     * the array immediately following the end of the set is set to
     * <tt>null</tt>.  (This is useful in determining the length of this
     * set <i>only</i> if the caller knows that this set does not contain
     * any null elements.)
     *
     * <p>If this set makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the elements
     * in the same order.
     *
     * <p>Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>Suppose <tt>x</tt> is a set known to contain only strings.
     * The following code can be used to dump the set into a newly allocated
     * array of <tt>String</tt>:
     *
     * <pre>
     *     String[] y = x.toArray(new String[0]);</pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of this set are to be
     *        stored, if it is big enough; otherwise, a new array of the same
     *        runtime type is allocated for this purpose.
     * @return an array containing all the elements in this set
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in this
     *         set
     * @throws NullPointerException if the specified array is null
     */
    public <T> T[] toArray(T[] a) {
        return al.toArray(a);
    }

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

    /**
     * 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
     */
    public boolean remove(Object o) {
        return al.remove(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
     */
    public boolean add(E e) {
        return al.addIfAbsent(e);
    }

    /**
     * Returns <tt>true</tt> if this set contains all of the elements of the
     * specified collection.  If the specified collection is also a set, this
     * method returns <tt>true</tt> if it is a <i>subset</i> of this set.
     *
     * @param  c collection to be checked for containment in this set
     * @return <tt>true</tt> if this set contains all of the elements of the
     *         specified collection
     * @throws NullPointerException if the specified collection is null
     * @see #contains(Object)
     */
    public boolean containsAll(Collection<?> c) {
        return al.containsAll(c);
    }

    /**
     * Adds all of the elements in the specified collection to this set if
     * they're not already present.  If the specified collection is also a
     * set, the <tt>addAll</tt> operation effectively modifies this set so
     * that its value is the <i>union</i> of the two sets.  The behavior of
     * this operation is undefined if the specified collection is modified
     * while the operation is in progress.
     *
     * @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 NullPointerException if the specified collection is null
     * @see #add(Object)
     */
    public boolean addAll(Collection<? extends E> c) {
        return al.addAllAbsent(c) > 0;
    }

    /**
     * Removes from this set all of its elements that are contained in the
     * specified collection.  If the specified collection is also a set,
     * this operation effectively modifies this set so that its value is the
     * <i>asymmetric set difference</i> of the two sets.
     *
     * @param  c collection containing elements to be removed from this set
     * @return <tt>true</tt> if this set changed as a result of the call
     * @throws ClassCastException if the class of an element of this set
     *         is incompatible with the specified collection (optional)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements (optional),
     *         or if the specified collection is null
     * @see #remove(Object)
     */
    public boolean removeAll(Collection<?> c) {
        return al.removeAll(c);
    }

    /**
     * Retains only the elements in this set that are contained in the
     * specified collection.  In other words, removes from this set all of
     * its elements that are not contained in the specified collection.  If
     * the specified collection is also a set, this operation effectively
     * modifies this set so that its value is the <i>intersection</i> of the
     * two sets.
     *
     * @param  c collection containing elements to be retained in this set
     * @return <tt>true</tt> if this set changed as a result of the call
     * @throws ClassCastException if the class of an element of this set
     *         is incompatible with the specified collection (optional)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements (optional),
     *         or if the specified collection is null
     * @see #remove(Object)
     */
    public boolean retainAll(Collection<?> c) {
        return al.retainAll(c);
    }

    /**
     * Returns an iterator over the elements contained in this set
     * in the order in which these elements were added.
     *
     * <p>The returned iterator provides a snapshot of the state of the set
     * when the iterator was constructed. No synchronization is needed while
     * traversing the iterator. The iterator does <em>NOT</em> support the
     * <tt>remove</tt> method.
     *
     * @return an iterator over the elements in this set
     */
    public Iterator<E> iterator() {
        return al.iterator();
    }

    /**
     * Compares the specified object with this set for equality.
     * Returns {@code true} if the specified object is the same object
     * as this object, or if it is also a {@link Set} and the elements
     * returned by an {@linkplain List#iterator() iterator} over the
     * specified set are the same as the elements returned by an
     * iterator over this set.  More formally, the two iterators are
     * considered to return the same elements if they return the same
     * number of elements and for every element {@code e1} returned by
     * the iterator over the specified set, there is an element
     * {@code e2} returned by the iterator over this set such that
     * {@code (e1==null ? e2==null : e1.equals(e2))}.
     *
     * @param o object to be compared for equality with this set
     * @return {@code true} if the specified object is equal to this set
     */
    public boolean equals(Object o) {
        if (o == this)
            return true;
        if (!(o instanceof Set))
            return false;
        Set<?> set = (Set<?>)(o);
        Iterator<?> it = set.iterator();

        // Uses O(n^2) algorithm that is only appropriate
        // for small sets, which CopyOnWriteArraySets should be.

        //  Use a single snapshot of underlying array
        Object[] elements = al.getArray();
        int len = elements.length;
        // Mark matched elements to avoid re-checking
        boolean[] matched = new boolean[len];
        int k = 0;
        outer: while (it.hasNext()) {
            if (++k > len)
                return false;
            Object x = it.next();
            for (int i = 0; i < len; ++i) {
                if (!matched[i] && eq(x, elements[i])) {
                    matched[i] = true;
                    continue outer;
                }
            }
            return false;
        }
        return k == len;
    }

    /**
     * Test for equality, coping with nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null ? o2 == null : o1.equals(o2));
    }
}
Revision:	1.34
Committed:	Sun May 28 23:36:29 2006 UTC (18 years ago) by jsr166
Branch:	MAIN
Changes since 1.33:	+1 -1 lines
Log Message:	Location of Collections Guide has changed
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8			import java.util.*;
9
10			/**
11	jsr166	1.26	* A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
12			* for all of its operations. Thus, it shares the same basic properties:
13	tim	1.1	* <ul>
14	dholmes	1.7	* <li>It is best suited for applications in which set sizes generally
15	tim	1.1	* stay small, read-only operations
16			* vastly outnumber mutative operations, and you need
17			* to prevent interference among threads during traversal.
18	dl	1.16	* <li>It is thread-safe.
19	jsr166	1.26	* <li>Mutative operations (<tt>add</tt>, <tt>set</tt>, <tt>remove</tt>, etc.)
20			* are expensive since they usually entail copying the entire underlying
21			* array.
22			* <li>Iterators do not support the mutative <tt>remove</tt> operation.
23	dl	1.18	* <li>Traversal via iterators is fast and cannot encounter
24	tim	1.1	* interference from other threads. Iterators rely on
25			* unchanging snapshots of the array at the time the iterators were
26	jsr166	1.26	* constructed.
27	tim	1.1	* </ul>
28	dl	1.18	*
29			* <p> <b>Sample Usage.</b> The following code sketch uses a
30	jsr166	1.21	* copy-on-write set to maintain a set of Handler objects that
31			* perform some action upon state updates.
32	dl	1.18	*
33	tim	1.1	* <pre>
34	tim	1.6	* class Handler { void handle(); ... }
35	tim	1.1	*
36			* class X {
37	jsr166	1.29	* private final CopyOnWriteArraySet<Handler> handlers
38			* = new CopyOnWriteArraySet<Handler>();
39	tim	1.1	* public void addHandler(Handler h) { handlers.add(h); }
40			*
41			* private long internalState;
42			* private synchronized void changeState() { internalState = ...; }
43			*
44			* public void update() {
45			* changeState();
46	dl	1.18	* for (Handler handler : handlers)
47	dl	1.19	* handler.handle();
48	tim	1.1	* }
49			* }
50	tim	1.6	* </pre>
51	dl	1.14	*
52			* <p>This class is a member of the
53	jsr166	1.34	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
54	dl	1.14	* Java Collections Framework</a>.
55			*
56	dl	1.16	* @see CopyOnWriteArrayList
57	dl	1.4	* @since 1.5
58			* @author Doug Lea
59	dl	1.11	* @param <E> the type of elements held in this collection
60	dl	1.4	*/
61	tim	1.1	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
62	dl	1.18	implements java.io.Serializable {
63	dl	1.8	private static final long serialVersionUID = 5457747651344034263L;
64	tim	1.1
65			private final CopyOnWriteArrayList<E> al;
66
67			/**
68	dl	1.15	* Creates an empty set.
69	tim	1.1	*/
70			public CopyOnWriteArraySet() {
71			al = new CopyOnWriteArrayList<E>();
72			}
73
74			/**
75	dl	1.15	* Creates a set containing all of the elements of the specified
76	jsr166	1.23	* collection.
77	jsr166	1.25	*
78	jsr166	1.23	* @param c the collection of elements to initially contain
79			* @throws NullPointerException if the specified collection is null
80	tim	1.1	*/
81	tim	1.12	public CopyOnWriteArraySet(Collection<? extends E> c) {
82	tim	1.1	al = new CopyOnWriteArrayList<E>();
83			al.addAllAbsent(c);
84			}
85
86	jsr166	1.26	/**
87			* Returns the number of elements in this set.
88			*
89			* @return the number of elements in this set
90			*/
91			public int size() {
92			return al.size();
93			}
94
95			/**
96			* Returns <tt>true</tt> if this set contains no elements.
97			*
98			* @return <tt>true</tt> if this set contains no elements
99			*/
100			public boolean isEmpty() {
101			return al.isEmpty();
102			}
103
104			/**
105			* Returns <tt>true</tt> if this set contains the specified element.
106			* More formally, returns <tt>true</tt> if and only if this set
107	jsr166	1.28	* contains an element <tt>e</tt> such that
108	jsr166	1.26	* <tt>(o==null ? e==null : o.equals(e))</tt>.
109			*
110			* @param o element whose presence in this set is to be tested
111			* @return <tt>true</tt> if this set contains the specified element
112			*/
113			public boolean contains(Object o) {
114			return al.contains(o);
115			}
116
117			/**
118			* Returns an array containing all of the elements in this set.
119			* If this set makes any guarantees as to what order its elements
120			* are returned by its iterator, this method must return the
121			* elements in the same order.
122			*
123			* <p>The returned array will be "safe" in that no references to it
124			* are maintained by this set. (In other words, this method must
125			* allocate a new array even if this set is backed by an array).
126			* The caller is thus free to modify the returned array.
127			*
128			* <p>This method acts as bridge between array-based and collection-based
129			* APIs.
130			*
131			* @return an array containing all the elements in this set
132			*/
133			public Object[] toArray() {
134			return al.toArray();
135			}
136
137			/**
138			* Returns an array containing all of the elements in this set; the
139			* runtime type of the returned array is that of the specified array.
140			* If the set fits in the specified array, it is returned therein.
141			* Otherwise, a new array is allocated with the runtime type of the
142			* specified array and the size of this set.
143			*
144			* <p>If this set fits in the specified array with room to spare
145			* (i.e., the array has more elements than this set), the element in
146			* the array immediately following the end of the set is set to
147			* <tt>null</tt>. (This is useful in determining the length of this
148			* set <i>only</i> if the caller knows that this set does not contain
149			* any null elements.)
150			*
151			* <p>If this set makes any guarantees as to what order its elements
152			* are returned by its iterator, this method must return the elements
153			* in the same order.
154			*
155			* <p>Like the {@link #toArray()} method, this method acts as bridge between
156			* array-based and collection-based APIs. Further, this method allows
157			* precise control over the runtime type of the output array, and may,
158			* under certain circumstances, be used to save allocation costs.
159			*
160			* <p>Suppose <tt>x</tt> is a set known to contain only strings.
161			* The following code can be used to dump the set into a newly allocated
162			* array of <tt>String</tt>:
163			*
164			* <pre>
165			* String[] y = x.toArray(new String[0]);</pre>
166			*
167			* Note that <tt>toArray(new Object[0])</tt> is identical in function to
168			* <tt>toArray()</tt>.
169			*
170			* @param a the array into which the elements of this set are to be
171			* stored, if it is big enough; otherwise, a new array of the same
172			* runtime type is allocated for this purpose.
173			* @return an array containing all the elements in this set
174			* @throws ArrayStoreException if the runtime type of the specified array
175			* is not a supertype of the runtime type of every element in this
176			* set
177			* @throws NullPointerException if the specified array is null
178			*/
179			public <T> T[] toArray(T[] a) {
180			return al.toArray(a);
181			}
182
183			/**
184			* Removes all of the elements from this set.
185	jsr166	1.27	* The set will be empty after this call returns.
186	jsr166	1.26	*/
187			public void clear() {
188			al.clear();
189			}
190
191			/**
192			* Removes the specified element from this set if it is present.
193			* More formally, removes an element <tt>e</tt> such that
194	jsr166	1.28	* <tt>(o==null ? e==null : o.equals(e))</tt>,
195			* if this set contains such an element. Returns <tt>true</tt> if
196			* this set contained the element (or equivalently, if this set
197			* changed as a result of the call). (This set will not contain the
198	jsr166	1.26	* element once the call returns.)
199			*
200			* @param o object to be removed from this set, if present
201			* @return <tt>true</tt> if this set contained the specified element
202			*/
203			public boolean remove(Object o) {
204			return al.remove(o);
205			}
206
207			/**
208			* Adds the specified element to this set if it is not already present.
209	jsr166	1.28	* More formally, adds the specified element <tt>e</tt> to this set if
210			* the set contains no element <tt>e2</tt> such that
211			* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
212			* If this set already contains the element, the call leaves the set
213			* unchanged and returns <tt>false</tt>.
214	jsr166	1.26	*
215			* @param e element to be added to this set
216			* @return <tt>true</tt> if this set did not already contain the specified
217			* element
218			*/
219			public boolean add(E e) {
220			return al.addIfAbsent(e);
221			}
222	tim	1.1
223	jsr166	1.26	/**
224			* Returns <tt>true</tt> if this set contains all of the elements of the
225			* specified collection. If the specified collection is also a set, this
226			* method returns <tt>true</tt> if it is a <i>subset</i> of this set.
227			*
228			* @param c collection to be checked for containment in this set
229			* @return <tt>true</tt> if this set contains all of the elements of the
230			* specified collection
231			* @throws NullPointerException if the specified collection is null
232			* @see #contains(Object)
233			*/
234			public boolean containsAll(Collection<?> c) {
235			return al.containsAll(c);
236			}
237
238			/**
239			* Adds all of the elements in the specified collection to this set if
240			* they're not already present. If the specified collection is also a
241			* set, the <tt>addAll</tt> operation effectively modifies this set so
242			* that its value is the <i>union</i> of the two sets. The behavior of
243	jsr166	1.28	* this operation is undefined if the specified collection is modified
244	jsr166	1.26	* while the operation is in progress.
245			*
246			* @param c collection containing elements to be added to this set
247			* @return <tt>true</tt> if this set changed as a result of the call
248			* @throws NullPointerException if the specified collection is null
249			* @see #add(Object)
250			*/
251			public boolean addAll(Collection<? extends E> c) {
252			return al.addAllAbsent(c) > 0;
253			}
254
255			/**
256			* Removes from this set all of its elements that are contained in the
257			* specified collection. If the specified collection is also a set,
258			* this operation effectively modifies this set so that its value is the
259			* <i>asymmetric set difference</i> of the two sets.
260			*
261			* @param c collection containing elements to be removed from this set
262			* @return <tt>true</tt> if this set changed as a result of the call
263			* @throws ClassCastException if the class of an element of this set
264			* is incompatible with the specified collection (optional)
265			* @throws NullPointerException if this set contains a null element and the
266			* specified collection does not permit null elements (optional),
267			* or if the specified collection is null
268			* @see #remove(Object)
269			*/
270			public boolean removeAll(Collection<?> c) {
271			return al.removeAll(c);
272			}
273
274			/**
275			* Retains only the elements in this set that are contained in the
276			* specified collection. In other words, removes from this set all of
277			* its elements that are not contained in the specified collection. If
278			* the specified collection is also a set, this operation effectively
279			* modifies this set so that its value is the <i>intersection</i> of the
280			* two sets.
281			*
282			* @param c collection containing elements to be retained in this set
283			* @return <tt>true</tt> if this set changed as a result of the call
284			* @throws ClassCastException if the class of an element of this set
285			* is incompatible with the specified collection (optional)
286			* @throws NullPointerException if this set contains a null element and the
287			* specified collection does not permit null elements (optional),
288			* or if the specified collection is null
289			* @see #remove(Object)
290			*/
291			public boolean retainAll(Collection<?> c) {
292			return al.retainAll(c);
293			}
294	tim	1.1
295	dl	1.20	/**
296	jsr166	1.24	* Returns an iterator over the elements contained in this set
297	dl	1.20	* in the order in which these elements were added.
298	jsr166	1.26	*
299			* <p>The returned iterator provides a snapshot of the state of the set
300			* when the iterator was constructed. No synchronization is needed while
301			* traversing the iterator. The iterator does <em>NOT</em> support the
302			* <tt>remove</tt> method.
303			*
304			* @return an iterator over the elements in this set
305	dl	1.20	*/
306	jsr166	1.26	public Iterator<E> iterator() {
307			return al.iterator();
308			}
309	dl	1.20
310	dl	1.30	/**
311			* Compares the specified object with this set for equality.
312	jsr166	1.33	* Returns {@code true} if the specified object is the same object
313			* as this object, or if it is also a {@link Set} and the elements
314			* returned by an {@linkplain List#iterator() iterator} over the
315			* specified set are the same as the elements returned by an
316			* iterator over this set. More formally, the two iterators are
317			* considered to return the same elements if they return the same
318			* number of elements and for every element {@code e1} returned by
319			* the iterator over the specified set, there is an element
320			* {@code e2} returned by the iterator over this set such that
321			* {@code (e1==null ? e2==null : e1.equals(e2))}.
322	dl	1.30	*
323			* @param o object to be compared for equality with this set
324	jsr166	1.33	* @return {@code true} if the specified object is equal to this set
325	dl	1.30	*/
326			public boolean equals(Object o) {
327			if (o == this)
328			return true;
329			if (!(o instanceof Set))
330			return false;
331			Set<?> set = (Set<?>)(o);
332	jsr166	1.33	Iterator<?> it = set.iterator();
333	dl	1.30
334			// Uses O(n^2) algorithm that is only appropriate
335			// for small sets, which CopyOnWriteArraySets should be.
336
337			// Use a single snapshot of underlying array
338			Object[] elements = al.getArray();
339			int len = elements.length;
340			// Mark matched elements to avoid re-checking
341			boolean[] matched = new boolean[len];
342			int k = 0;
343	jsr166	1.33	outer: while (it.hasNext()) {
344	dl	1.30	if (++k > len)
345			return false;
346	jsr166	1.33	Object x = it.next();
347	dl	1.30	for (int i = 0; i < len; ++i) {
348			if (!matched[i] && eq(x, elements[i])) {
349			matched[i] = true;
350	jsr166	1.33	continue outer;
351	dl	1.30	}
352			}
353	jsr166	1.33	return false;
354	dl	1.30	}
355			return k == len;
356			}
357	jsr166	1.32
358	dl	1.30	/**
359			* Test for equality, coping with nulls.
360			*/
361			private static boolean eq(Object o1, Object o2) {
362			return (o1 == null ? o2 == null : o1.equals(o2));
363			}
364	tim	1.1	}