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.Set;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.stream.Stream;
import java.util.Spliterator;
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 Stream<E> stream() {
        int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED |
            Streams.STREAM_IS_DISTINCT;
        Object[] a = al.getArray();
        int n = a.length;
        return Streams.stream
            (() -> new CopyOnWriteArrayList.COWSpliterator<E>(a, 0, n), flags);
    }
    public Stream<E> parallelStream() {
        int flags = Streams.STREAM_IS_ORDERED | Streams.STREAM_IS_SIZED |
            Streams.STREAM_IS_DISTINCT;
        Object[] a = al.getArray();
        int n = a.length;
        return Streams.parallelStream
            (() -> new CopyOnWriteArrayList.COWSpliterator<E>(a, 0, n), flags);
    }

    /**
     * Tests for equality, coping with nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null) ? o2 == null : o1.equals(o2);
    }
}
Revision:	1.47
Committed:	Sat Jan 19 17:28:55 2013 UTC (11 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.46:	+1 -1 lines
Log Message:	fix javadoc warning
#	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			import java.util.Set;
10			import java.util.AbstractSet;
11			import java.util.Iterator;
12			import java.util.stream.Stream;
13			import java.util.Spliterator;
14			import java.util.stream.Streams;
15	tim	1.1
16			/**
17	jsr166	1.26	* A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
18			* for all of its operations. Thus, it shares the same basic properties:
19	tim	1.1	* <ul>
20	dholmes	1.7	* <li>It is best suited for applications in which set sizes generally
21	tim	1.1	* stay small, read-only operations
22			* vastly outnumber mutative operations, and you need
23			* to prevent interference among threads during traversal.
24	dl	1.16	* <li>It is thread-safe.
25	jsr166	1.44	* <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
26	jsr166	1.26	* are expensive since they usually entail copying the entire underlying
27			* array.
28	jsr166	1.44	* <li>Iterators do not support the mutative {@code remove} operation.
29	dl	1.18	* <li>Traversal via iterators is fast and cannot encounter
30	tim	1.1	* interference from other threads. Iterators rely on
31			* unchanging snapshots of the array at the time the iterators were
32	jsr166	1.26	* constructed.
33	tim	1.1	* </ul>
34	dl	1.18	*
35	jsr166	1.42	* <p><b>Sample Usage.</b> The following code sketch uses a
36	jsr166	1.21	* copy-on-write set to maintain a set of Handler objects that
37			* perform some action upon state updates.
38	dl	1.18	*
39	jsr166	1.37	* <pre> {@code
40	tim	1.6	* class Handler { void handle(); ... }
41	tim	1.1	*
42			* class X {
43	jsr166	1.37	* private final CopyOnWriteArraySet<Handler> handlers
44			* = new CopyOnWriteArraySet<Handler>();
45			* public void addHandler(Handler h) { handlers.add(h); }
46	tim	1.1	*
47	jsr166	1.37	* private long internalState;
48			* private synchronized void changeState() { internalState = ...; }
49	tim	1.1	*
50	jsr166	1.37	* public void update() {
51			* changeState();
52			* for (Handler handler : handlers)
53	jsr166	1.43	* handler.handle();
54	jsr166	1.37	* }
55			* }}</pre>
56	dl	1.14	*
57			* <p>This class is a member of the
58	jsr166	1.34	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
59	dl	1.14	* Java Collections Framework</a>.
60			*
61	dl	1.16	* @see CopyOnWriteArrayList
62	dl	1.4	* @since 1.5
63			* @author Doug Lea
64	dl	1.11	* @param <E> the type of elements held in this collection
65	dl	1.4	*/
66	tim	1.1	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
67	dl	1.18	implements java.io.Serializable {
68	dl	1.8	private static final long serialVersionUID = 5457747651344034263L;
69	tim	1.1
70			private final CopyOnWriteArrayList<E> al;
71
72			/**
73	dl	1.15	* Creates an empty set.
74	tim	1.1	*/
75			public CopyOnWriteArraySet() {
76			al = new CopyOnWriteArrayList<E>();
77			}
78
79			/**
80	dl	1.15	* Creates a set containing all of the elements of the specified
81	jsr166	1.23	* collection.
82	jsr166	1.25	*
83	jsr166	1.23	* @param c the collection of elements to initially contain
84			* @throws NullPointerException if the specified collection is null
85	tim	1.1	*/
86	tim	1.12	public CopyOnWriteArraySet(Collection<? extends E> c) {
87	tim	1.1	al = new CopyOnWriteArrayList<E>();
88			al.addAllAbsent(c);
89			}
90
91	jsr166	1.26	/**
92			* Returns the number of elements in this set.
93			*
94			* @return the number of elements in this set
95			*/
96			public int size() {
97	jsr166	1.36	return al.size();
98	jsr166	1.26	}
99
100			/**
101	jsr166	1.44	* Returns {@code true} if this set contains no elements.
102	jsr166	1.26	*
103	jsr166	1.44	* @return {@code true} if this set contains no elements
104	jsr166	1.26	*/
105			public boolean isEmpty() {
106	jsr166	1.36	return al.isEmpty();
107	jsr166	1.26	}
108
109			/**
110	jsr166	1.44	* Returns {@code true} if this set contains the specified element.
111			* More formally, returns {@code true} if and only if this set
112			* contains an element {@code e} such that
113	jsr166	1.26	* <tt>(o==null ? e==null : o.equals(e))</tt>.
114			*
115			* @param o element whose presence in this set is to be tested
116	jsr166	1.44	* @return {@code true} if this set contains the specified element
117	jsr166	1.26	*/
118			public boolean contains(Object o) {
119	jsr166	1.36	return al.contains(o);
120	jsr166	1.26	}
121
122			/**
123			* Returns an array containing all of the elements in this set.
124			* If this set makes any guarantees as to what order its elements
125			* are returned by its iterator, this method must return the
126			* elements in the same order.
127			*
128			* <p>The returned array will be "safe" in that no references to it
129			* are maintained by this set. (In other words, this method must
130			* allocate a new array even if this set is backed by an array).
131			* The caller is thus free to modify the returned array.
132			*
133			* <p>This method acts as bridge between array-based and collection-based
134			* APIs.
135			*
136			* @return an array containing all the elements in this set
137			*/
138			public Object[] toArray() {
139	jsr166	1.36	return al.toArray();
140	jsr166	1.26	}
141
142			/**
143			* Returns an array containing all of the elements in this set; the
144			* runtime type of the returned array is that of the specified array.
145			* If the set fits in the specified array, it is returned therein.
146			* Otherwise, a new array is allocated with the runtime type of the
147			* specified array and the size of this set.
148			*
149			* <p>If this set fits in the specified array with room to spare
150			* (i.e., the array has more elements than this set), the element in
151			* the array immediately following the end of the set is set to
152	jsr166	1.44	* {@code null}. (This is useful in determining the length of this
153	jsr166	1.26	* set <i>only</i> if the caller knows that this set does not contain
154			* any null elements.)
155			*
156			* <p>If this set makes any guarantees as to what order its elements
157			* are returned by its iterator, this method must return the elements
158			* in the same order.
159			*
160			* <p>Like the {@link #toArray()} method, this method acts as bridge between
161			* array-based and collection-based APIs. Further, this method allows
162			* precise control over the runtime type of the output array, and may,
163			* under certain circumstances, be used to save allocation costs.
164			*
165	jsr166	1.44	* <p>Suppose {@code x} is a set known to contain only strings.
166	jsr166	1.26	* The following code can be used to dump the set into a newly allocated
167	jsr166	1.44	* array of {@code String}:
168	jsr166	1.26	*
169	jsr166	1.40	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
170	jsr166	1.26	*
171	jsr166	1.44	* Note that {@code toArray(new Object[0])} is identical in function to
172			* {@code toArray()}.
173	jsr166	1.26	*
174			* @param a the array into which the elements of this set are to be
175			* stored, if it is big enough; otherwise, a new array of the same
176			* runtime type is allocated for this purpose.
177			* @return an array containing all the elements in this set
178			* @throws ArrayStoreException if the runtime type of the specified array
179			* is not a supertype of the runtime type of every element in this
180			* set
181			* @throws NullPointerException if the specified array is null
182			*/
183			public <T> T[] toArray(T[] a) {
184	jsr166	1.36	return al.toArray(a);
185	jsr166	1.26	}
186
187			/**
188			* Removes all of the elements from this set.
189	jsr166	1.27	* The set will be empty after this call returns.
190	jsr166	1.26	*/
191			public void clear() {
192			al.clear();
193			}
194
195			/**
196			* Removes the specified element from this set if it is present.
197	jsr166	1.44	* More formally, removes an element {@code e} such that
198	jsr166	1.28	* <tt>(o==null ? e==null : o.equals(e))</tt>,
199	jsr166	1.44	* if this set contains such an element. Returns {@code true} if
200	jsr166	1.28	* this set contained the element (or equivalently, if this set
201			* changed as a result of the call). (This set will not contain the
202	jsr166	1.26	* element once the call returns.)
203			*
204			* @param o object to be removed from this set, if present
205	jsr166	1.44	* @return {@code true} if this set contained the specified element
206	jsr166	1.26	*/
207			public boolean remove(Object o) {
208	jsr166	1.36	return al.remove(o);
209	jsr166	1.26	}
210
211			/**
212			* Adds the specified element to this set if it is not already present.
213	jsr166	1.44	* More formally, adds the specified element {@code e} to this set if
214			* the set contains no element {@code e2} such that
215	jsr166	1.28	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
216			* If this set already contains the element, the call leaves the set
217	jsr166	1.44	* unchanged and returns {@code false}.
218	jsr166	1.26	*
219			* @param e element to be added to this set
220	jsr166	1.44	* @return {@code true} if this set did not already contain the specified
221	jsr166	1.26	* element
222			*/
223			public boolean add(E e) {
224	jsr166	1.36	return al.addIfAbsent(e);
225	jsr166	1.26	}
226	tim	1.1
227	jsr166	1.26	/**
228	jsr166	1.44	* Returns {@code true} if this set contains all of the elements of the
229	jsr166	1.26	* specified collection. If the specified collection is also a set, this
230	jsr166	1.44	* method returns {@code true} if it is a <i>subset</i> of this set.
231	jsr166	1.26	*
232			* @param c collection to be checked for containment in this set
233	jsr166	1.44	* @return {@code true} if this set contains all of the elements of the
234	jsr166	1.36	* specified collection
235	jsr166	1.26	* @throws NullPointerException if the specified collection is null
236			* @see #contains(Object)
237			*/
238			public boolean containsAll(Collection<?> c) {
239	jsr166	1.36	return al.containsAll(c);
240	jsr166	1.26	}
241
242			/**
243			* Adds all of the elements in the specified collection to this set if
244			* they're not already present. If the specified collection is also a
245	jsr166	1.44	* set, the {@code addAll} operation effectively modifies this set so
246	jsr166	1.26	* that its value is the <i>union</i> of the two sets. The behavior of
247	jsr166	1.28	* this operation is undefined if the specified collection is modified
248	jsr166	1.26	* while the operation is in progress.
249			*
250			* @param c collection containing elements to be added to this set
251	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
252	jsr166	1.26	* @throws NullPointerException if the specified collection is null
253			* @see #add(Object)
254			*/
255			public boolean addAll(Collection<? extends E> c) {
256	jsr166	1.36	return al.addAllAbsent(c) > 0;
257	jsr166	1.26	}
258
259			/**
260			* Removes from this set all of its elements that are contained in the
261			* specified collection. If the specified collection is also a set,
262			* this operation effectively modifies this set so that its value is the
263			* <i>asymmetric set difference</i> of the two sets.
264			*
265			* @param c collection containing elements to be removed from this set
266	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
267	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
268			* is incompatible with the specified collection (optional)
269			* @throws NullPointerException if this set contains a null element and the
270			* specified collection does not permit null elements (optional),
271			* or if the specified collection is null
272			* @see #remove(Object)
273			*/
274			public boolean removeAll(Collection<?> c) {
275	jsr166	1.36	return al.removeAll(c);
276	jsr166	1.26	}
277
278			/**
279			* Retains only the elements in this set that are contained in the
280			* specified collection. In other words, removes from this set all of
281			* its elements that are not contained in the specified collection. If
282			* the specified collection is also a set, this operation effectively
283			* modifies this set so that its value is the <i>intersection</i> of the
284			* two sets.
285			*
286			* @param c collection containing elements to be retained in this set
287	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
288	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
289			* is incompatible with the specified collection (optional)
290			* @throws NullPointerException if this set contains a null element and the
291			* specified collection does not permit null elements (optional),
292			* or if the specified collection is null
293			* @see #remove(Object)
294			*/
295			public boolean retainAll(Collection<?> c) {
296	jsr166	1.36	return al.retainAll(c);
297	jsr166	1.26	}
298	tim	1.1
299	dl	1.20	/**
300	jsr166	1.24	* Returns an iterator over the elements contained in this set
301	dl	1.20	* in the order in which these elements were added.
302	jsr166	1.26	*
303			* <p>The returned iterator provides a snapshot of the state of the set
304			* when the iterator was constructed. No synchronization is needed while
305			* traversing the iterator. The iterator does <em>NOT</em> support the
306	jsr166	1.44	* {@code remove} method.
307	jsr166	1.26	*
308			* @return an iterator over the elements in this set
309	dl	1.20	*/
310	jsr166	1.26	public Iterator<E> iterator() {
311	jsr166	1.36	return al.iterator();
312	jsr166	1.26	}
313	dl	1.20
314	dl	1.30	/**
315			* Compares the specified object with this set for equality.
316	jsr166	1.33	* Returns {@code true} if the specified object is the same object
317			* as this object, or if it is also a {@link Set} and the elements
318	jsr166	1.47	* returned by an {@linkplain Set#iterator() iterator} over the
319	jsr166	1.33	* specified set are the same as the elements returned by an
320			* iterator over this set. More formally, the two iterators are
321			* considered to return the same elements if they return the same
322			* number of elements and for every element {@code e1} returned by
323			* the iterator over the specified set, there is an element
324			* {@code e2} returned by the iterator over this set such that
325			* {@code (e1==null ? e2==null : e1.equals(e2))}.
326	dl	1.30	*
327			* @param o object to be compared for equality with this set
328	jsr166	1.33	* @return {@code true} if the specified object is equal to this set
329	dl	1.30	*/
330			public boolean equals(Object o) {
331			if (o == this)
332			return true;
333			if (!(o instanceof Set))
334			return false;
335			Set<?> set = (Set<?>)(o);
336	jsr166	1.36	Iterator<?> it = set.iterator();
337	dl	1.30
338			// Uses O(n^2) algorithm that is only appropriate
339			// for small sets, which CopyOnWriteArraySets should be.
340
341			// Use a single snapshot of underlying array
342	jsr166	1.36	Object[] elements = al.getArray();
343			int len = elements.length;
344	dl	1.30	// Mark matched elements to avoid re-checking
345			boolean[] matched = new boolean[len];
346			int k = 0;
347	jsr166	1.33	outer: while (it.hasNext()) {
348	dl	1.30	if (++k > len)
349			return false;
350	jsr166	1.33	Object x = it.next();
351	dl	1.30	for (int i = 0; i < len; ++i) {
352			if (!matched[i] && eq(x, elements[i])) {
353			matched[i] = true;
354	jsr166	1.36	continue outer;
355	dl	1.30	}
356			}
357	jsr166	1.36	return false;
358	dl	1.30	}
359			return k == len;
360			}
361	jsr166	1.32
362	dl	1.45	public Stream<E> stream() {
363	jsr166	1.46	int flags = Streams.STREAM_IS_ORDERED \| Streams.STREAM_IS_SIZED \|
364	dl	1.45	Streams.STREAM_IS_DISTINCT;
365			Object[] a = al.getArray();
366			int n = a.length;
367			return Streams.stream
368			(() -> new CopyOnWriteArrayList.COWSpliterator<E>(a, 0, n), flags);
369			}
370			public Stream<E> parallelStream() {
371	jsr166	1.46	int flags = Streams.STREAM_IS_ORDERED \| Streams.STREAM_IS_SIZED \|
372	dl	1.45	Streams.STREAM_IS_DISTINCT;
373			Object[] a = al.getArray();
374			int n = a.length;
375			return Streams.parallelStream
376			(() -> new CopyOnWriteArrayList.COWSpliterator<E>(a, 0, n), flags);
377			}
378
379	dl	1.30	/**
380	jsr166	1.41	* Tests for equality, coping with nulls.
381	dl	1.30	*/
382			private static boolean eq(Object o1, Object o2) {
383	jsr166	1.39	return (o1 == null) ? o2 == null : o1.equals(o2);
384	dl	1.30	}
385	tim	1.1	}