util/concurrent/CopyOnWriteArraySet.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;
import java.util.Collection;
import java.util.Collections;
import java.util.Set;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.stream.Stream;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.stream.Streams;

/**
 * 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 ({@code add}, {@code set}, {@code remove}, etc.)
 *      are expensive since they usually entail copying the entire underlying
 *      array.
 *  <li>Iterators do not support the mutative {@code remove} 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> {@code
 * class Handler { void handle(); ... }
 *
 * class X {
 *   private final CopyOnWriteArraySet<Handler> handlers
 *     = new CopyOnWriteArraySet<Handler>();
 *   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 {@code true} if this set contains no elements.
     *
     * @return {@code true} if this set contains no elements
     */
    public boolean isEmpty() {
        return al.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 element whose presence in this set is to be tested
     * @return {@code true} 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
     * {@code null}.  (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 {@code x} is a set known to contain only strings.
     * The following code can be used to dump the set into a newly allocated
     * array of {@code String}:
     *
     *  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
     *
     * Note that {@code toArray(new Object[0])} is identical in function to
     * {@code toArray()}.
     *
     * @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 {@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
     */
    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 {@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
     */
    public boolean add(E e) {
        return al.addIfAbsent(e);
    }

    /**
     * Returns {@code true} if this set contains all of the elements of the
     * specified collection.  If the specified collection is also a set, this
     * method returns {@code true} if it is a <i>subset</i> of this set.
     *
     * @param  c collection to be checked for containment in this set
     * @return {@code true} 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 {@code addAll} 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 {@code true} 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 {@code true} 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 {@code true} 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
     * {@code remove} 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 Set#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;
    }

    public Spliterator<E> spliterator() {
        return Spliterators.spliterator
            (al.getArray(), Spliterator.IMMUTABLE |
             Spliterator.DISTINCT | Spliterator.ORDERED);
    }

    /**
     * Tests for equality, coping with nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null) ? o2 == null : o1.equals(o2);
    }
}
Revision:	1.52
Committed:	Thu Apr 4 11:31:21 2013 UTC (11 years, 2 months ago) by dl
Branch:	MAIN
Changes since 1.51:	+1 -4 lines
Log Message:	Revert unintended commit
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3	jsr166	1.35	* Expert Group and released to the public domain, as explained at
4	jsr166	1.38	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.2	*/
6
7	tim	1.1	package java.util.concurrent;
8	dl	1.45	import java.util.Collection;
9	dl	1.48	import java.util.Collections;
10	dl	1.45	import java.util.Set;
11			import java.util.AbstractSet;
12			import java.util.Iterator;
13			import java.util.stream.Stream;
14			import java.util.Spliterator;
15	dl	1.50	import java.util.Spliterators;
16	dl	1.45	import java.util.stream.Streams;
17	tim	1.1
18			/**
19	jsr166	1.26	* A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
20			* for all of its operations. Thus, it shares the same basic properties:
21	tim	1.1	* <ul>
22	dholmes	1.7	* <li>It is best suited for applications in which set sizes generally
23	tim	1.1	* stay small, read-only operations
24			* vastly outnumber mutative operations, and you need
25			* to prevent interference among threads during traversal.
26	dl	1.16	* <li>It is thread-safe.
27	jsr166	1.44	* <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
28	jsr166	1.26	* are expensive since they usually entail copying the entire underlying
29			* array.
30	jsr166	1.44	* <li>Iterators do not support the mutative {@code remove} operation.
31	dl	1.18	* <li>Traversal via iterators is fast and cannot encounter
32	tim	1.1	* interference from other threads. Iterators rely on
33			* unchanging snapshots of the array at the time the iterators were
34	jsr166	1.26	* constructed.
35	tim	1.1	* </ul>
36	dl	1.18	*
37	jsr166	1.42	* <p><b>Sample Usage.</b> The following code sketch uses a
38	jsr166	1.21	* copy-on-write set to maintain a set of Handler objects that
39			* perform some action upon state updates.
40	dl	1.18	*
41	jsr166	1.37	* <pre> {@code
42	tim	1.6	* class Handler { void handle(); ... }
43	tim	1.1	*
44			* class X {
45	jsr166	1.37	* private final CopyOnWriteArraySet<Handler> handlers
46			* = new CopyOnWriteArraySet<Handler>();
47			* public void addHandler(Handler h) { handlers.add(h); }
48	tim	1.1	*
49	jsr166	1.37	* private long internalState;
50			* private synchronized void changeState() { internalState = ...; }
51	tim	1.1	*
52	jsr166	1.37	* public void update() {
53			* changeState();
54			* for (Handler handler : handlers)
55	jsr166	1.43	* handler.handle();
56	jsr166	1.37	* }
57			* }}</pre>
58	dl	1.14	*
59			* <p>This class is a member of the
60	jsr166	1.34	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
61	dl	1.14	* Java Collections Framework</a>.
62			*
63	dl	1.16	* @see CopyOnWriteArrayList
64	dl	1.4	* @since 1.5
65			* @author Doug Lea
66	dl	1.11	* @param <E> the type of elements held in this collection
67	dl	1.4	*/
68	tim	1.1	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
69	dl	1.18	implements java.io.Serializable {
70	dl	1.8	private static final long serialVersionUID = 5457747651344034263L;
71	tim	1.1
72			private final CopyOnWriteArrayList<E> al;
73
74			/**
75	dl	1.15	* Creates an empty set.
76	tim	1.1	*/
77			public CopyOnWriteArraySet() {
78			al = new CopyOnWriteArrayList<E>();
79			}
80
81			/**
82	dl	1.15	* Creates a set containing all of the elements of the specified
83	jsr166	1.23	* collection.
84	jsr166	1.25	*
85	jsr166	1.23	* @param c the collection of elements to initially contain
86			* @throws NullPointerException if the specified collection is null
87	tim	1.1	*/
88	tim	1.12	public CopyOnWriteArraySet(Collection<? extends E> c) {
89	tim	1.1	al = new CopyOnWriteArrayList<E>();
90			al.addAllAbsent(c);
91			}
92
93	jsr166	1.26	/**
94			* Returns the number of elements in this set.
95			*
96			* @return the number of elements in this set
97			*/
98			public int size() {
99	jsr166	1.36	return al.size();
100	jsr166	1.26	}
101
102			/**
103	jsr166	1.44	* Returns {@code true} if this set contains no elements.
104	jsr166	1.26	*
105	jsr166	1.44	* @return {@code true} if this set contains no elements
106	jsr166	1.26	*/
107			public boolean isEmpty() {
108	jsr166	1.36	return al.isEmpty();
109	jsr166	1.26	}
110
111			/**
112	jsr166	1.44	* Returns {@code true} if this set contains the specified element.
113			* More formally, returns {@code true} if and only if this set
114			* contains an element {@code e} such that
115	jsr166	1.26	* <tt>(o==null ? e==null : o.equals(e))</tt>.
116			*
117			* @param o element whose presence in this set is to be tested
118	jsr166	1.44	* @return {@code true} if this set contains the specified element
119	jsr166	1.26	*/
120			public boolean contains(Object o) {
121	jsr166	1.36	return al.contains(o);
122	jsr166	1.26	}
123
124			/**
125			* Returns an array containing all of the elements in this set.
126			* If this set makes any guarantees as to what order its elements
127			* are returned by its iterator, this method must return the
128			* elements in the same order.
129			*
130			* <p>The returned array will be "safe" in that no references to it
131			* are maintained by this set. (In other words, this method must
132			* allocate a new array even if this set is backed by an array).
133			* The caller is thus free to modify the returned array.
134			*
135			* <p>This method acts as bridge between array-based and collection-based
136			* APIs.
137			*
138			* @return an array containing all the elements in this set
139			*/
140			public Object[] toArray() {
141	jsr166	1.36	return al.toArray();
142	jsr166	1.26	}
143
144			/**
145			* Returns an array containing all of the elements in this set; the
146			* runtime type of the returned array is that of the specified array.
147			* If the set fits in the specified array, it is returned therein.
148			* Otherwise, a new array is allocated with the runtime type of the
149			* specified array and the size of this set.
150			*
151			* <p>If this set fits in the specified array with room to spare
152			* (i.e., the array has more elements than this set), the element in
153			* the array immediately following the end of the set is set to
154	jsr166	1.44	* {@code null}. (This is useful in determining the length of this
155	jsr166	1.26	* set <i>only</i> if the caller knows that this set does not contain
156			* any null elements.)
157			*
158			* <p>If this set makes any guarantees as to what order its elements
159			* are returned by its iterator, this method must return the elements
160			* in the same order.
161			*
162			* <p>Like the {@link #toArray()} method, this method acts as bridge between
163			* array-based and collection-based APIs. Further, this method allows
164			* precise control over the runtime type of the output array, and may,
165			* under certain circumstances, be used to save allocation costs.
166			*
167	jsr166	1.44	* <p>Suppose {@code x} is a set known to contain only strings.
168	jsr166	1.26	* The following code can be used to dump the set into a newly allocated
169	jsr166	1.44	* array of {@code String}:
170	jsr166	1.26	*
171	jsr166	1.40	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
172	jsr166	1.26	*
173	jsr166	1.44	* Note that {@code toArray(new Object[0])} is identical in function to
174			* {@code toArray()}.
175	jsr166	1.26	*
176			* @param a the array into which the elements of this set are to be
177			* stored, if it is big enough; otherwise, a new array of the same
178			* runtime type is allocated for this purpose.
179			* @return an array containing all the elements in this set
180			* @throws ArrayStoreException if the runtime type of the specified array
181			* is not a supertype of the runtime type of every element in this
182			* set
183			* @throws NullPointerException if the specified array is null
184			*/
185			public <T> T[] toArray(T[] a) {
186	jsr166	1.36	return al.toArray(a);
187	jsr166	1.26	}
188
189			/**
190			* Removes all of the elements from this set.
191	jsr166	1.27	* The set will be empty after this call returns.
192	jsr166	1.26	*/
193			public void clear() {
194			al.clear();
195			}
196
197			/**
198			* Removes the specified element from this set if it is present.
199	jsr166	1.44	* More formally, removes an element {@code e} such that
200	jsr166	1.28	* <tt>(o==null ? e==null : o.equals(e))</tt>,
201	jsr166	1.44	* if this set contains such an element. Returns {@code true} if
202	jsr166	1.28	* this set contained the element (or equivalently, if this set
203			* changed as a result of the call). (This set will not contain the
204	jsr166	1.26	* element once the call returns.)
205			*
206			* @param o object to be removed from this set, if present
207	jsr166	1.44	* @return {@code true} if this set contained the specified element
208	jsr166	1.26	*/
209			public boolean remove(Object o) {
210	jsr166	1.36	return al.remove(o);
211	jsr166	1.26	}
212
213			/**
214			* Adds the specified element to this set if it is not already present.
215	jsr166	1.44	* More formally, adds the specified element {@code e} to this set if
216			* the set contains no element {@code e2} such that
217	jsr166	1.28	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
218			* If this set already contains the element, the call leaves the set
219	jsr166	1.44	* unchanged and returns {@code false}.
220	jsr166	1.26	*
221			* @param e element to be added to this set
222	jsr166	1.44	* @return {@code true} if this set did not already contain the specified
223	jsr166	1.26	* element
224			*/
225			public boolean add(E e) {
226	jsr166	1.36	return al.addIfAbsent(e);
227	jsr166	1.26	}
228	tim	1.1
229	jsr166	1.26	/**
230	jsr166	1.44	* Returns {@code true} if this set contains all of the elements of the
231	jsr166	1.26	* specified collection. If the specified collection is also a set, this
232	jsr166	1.44	* method returns {@code true} if it is a <i>subset</i> of this set.
233	jsr166	1.26	*
234			* @param c collection to be checked for containment in this set
235	jsr166	1.44	* @return {@code true} if this set contains all of the elements of the
236	jsr166	1.36	* specified collection
237	jsr166	1.26	* @throws NullPointerException if the specified collection is null
238			* @see #contains(Object)
239			*/
240			public boolean containsAll(Collection<?> c) {
241	jsr166	1.36	return al.containsAll(c);
242	jsr166	1.26	}
243
244			/**
245			* Adds all of the elements in the specified collection to this set if
246			* they're not already present. If the specified collection is also a
247	jsr166	1.44	* set, the {@code addAll} operation effectively modifies this set so
248	jsr166	1.26	* that its value is the <i>union</i> of the two sets. The behavior of
249	jsr166	1.28	* this operation is undefined if the specified collection is modified
250	jsr166	1.26	* while the operation is in progress.
251			*
252			* @param c collection containing elements to be added to this set
253	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
254	jsr166	1.26	* @throws NullPointerException if the specified collection is null
255			* @see #add(Object)
256			*/
257			public boolean addAll(Collection<? extends E> c) {
258	dl	1.52	return al.addAllAbsent(c) > 0;
259	jsr166	1.26	}
260
261			/**
262			* Removes from this set all of its elements that are contained in the
263			* specified collection. If the specified collection is also a set,
264			* this operation effectively modifies this set so that its value is the
265			* <i>asymmetric set difference</i> of the two sets.
266			*
267			* @param c collection containing elements to be removed from this set
268	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
269	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
270			* is incompatible with the specified collection (optional)
271			* @throws NullPointerException if this set contains a null element and the
272			* specified collection does not permit null elements (optional),
273			* or if the specified collection is null
274			* @see #remove(Object)
275			*/
276			public boolean removeAll(Collection<?> c) {
277	jsr166	1.36	return al.removeAll(c);
278	jsr166	1.26	}
279
280			/**
281			* Retains only the elements in this set that are contained in the
282			* specified collection. In other words, removes from this set all of
283			* its elements that are not contained in the specified collection. If
284			* the specified collection is also a set, this operation effectively
285			* modifies this set so that its value is the <i>intersection</i> of the
286			* two sets.
287			*
288			* @param c collection containing elements to be retained in this set
289	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
290	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
291			* is incompatible with the specified collection (optional)
292			* @throws NullPointerException if this set contains a null element and the
293			* specified collection does not permit null elements (optional),
294			* or if the specified collection is null
295			* @see #remove(Object)
296			*/
297			public boolean retainAll(Collection<?> c) {
298	jsr166	1.36	return al.retainAll(c);
299	jsr166	1.26	}
300	tim	1.1
301	dl	1.20	/**
302	jsr166	1.24	* Returns an iterator over the elements contained in this set
303	dl	1.20	* in the order in which these elements were added.
304	jsr166	1.26	*
305			* <p>The returned iterator provides a snapshot of the state of the set
306			* when the iterator was constructed. No synchronization is needed while
307			* traversing the iterator. The iterator does <em>NOT</em> support the
308	jsr166	1.44	* {@code remove} method.
309	jsr166	1.26	*
310			* @return an iterator over the elements in this set
311	dl	1.20	*/
312	jsr166	1.26	public Iterator<E> iterator() {
313	jsr166	1.36	return al.iterator();
314	jsr166	1.26	}
315	dl	1.20
316	dl	1.30	/**
317			* Compares the specified object with this set for equality.
318	jsr166	1.33	* Returns {@code true} if the specified object is the same object
319			* as this object, or if it is also a {@link Set} and the elements
320	jsr166	1.47	* returned by an {@linkplain Set#iterator() iterator} over the
321	jsr166	1.33	* specified set are the same as the elements returned by an
322			* iterator over this set. More formally, the two iterators are
323			* considered to return the same elements if they return the same
324			* number of elements and for every element {@code e1} returned by
325			* the iterator over the specified set, there is an element
326			* {@code e2} returned by the iterator over this set such that
327			* {@code (e1==null ? e2==null : e1.equals(e2))}.
328	dl	1.30	*
329			* @param o object to be compared for equality with this set
330	jsr166	1.33	* @return {@code true} if the specified object is equal to this set
331	dl	1.30	*/
332			public boolean equals(Object o) {
333			if (o == this)
334			return true;
335			if (!(o instanceof Set))
336			return false;
337			Set<?> set = (Set<?>)(o);
338	jsr166	1.36	Iterator<?> it = set.iterator();
339	dl	1.30
340			// Uses O(n^2) algorithm that is only appropriate
341			// for small sets, which CopyOnWriteArraySets should be.
342
343			// Use a single snapshot of underlying array
344	jsr166	1.36	Object[] elements = al.getArray();
345			int len = elements.length;
346	dl	1.30	// Mark matched elements to avoid re-checking
347			boolean[] matched = new boolean[len];
348			int k = 0;
349	jsr166	1.33	outer: while (it.hasNext()) {
350	dl	1.30	if (++k > len)
351			return false;
352	jsr166	1.33	Object x = it.next();
353	dl	1.30	for (int i = 0; i < len; ++i) {
354			if (!matched[i] && eq(x, elements[i])) {
355			matched[i] = true;
356	jsr166	1.36	continue outer;
357	dl	1.30	}
358			}
359	jsr166	1.36	return false;
360	dl	1.30	}
361			return k == len;
362			}
363	jsr166	1.32
364	dl	1.51	public Spliterator<E> spliterator() {
365	dl	1.50	return Spliterators.spliterator
366	jsr166	1.49	(al.getArray(), Spliterator.IMMUTABLE \|
367	dl	1.48	Spliterator.DISTINCT \| Spliterator.ORDERED);
368			}
369
370	dl	1.30	/**
371	jsr166	1.41	* Tests for equality, coping with nulls.
372	dl	1.30	*/
373			private static boolean eq(Object o1, Object o2) {
374	jsr166	1.39	return (o1 == null) ? o2 == null : o1.equals(o2);
375	dl	1.30	}
376	tim	1.1	}