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.Spliterator;
import java.util.Spliterators;
import java.util.function.Predicate;
import java.util.function.Consumer;

/**
 * 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) {
        if (c.getClass() == CopyOnWriteArraySet.class) {
            @SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
                (CopyOnWriteArraySet<E>)c;
            al = new CopyOnWriteArrayList<E>(cc.al);
        }
        else {
            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 boolean removeIf(Predicate<? super E> filter) {
        return al.removeIf(filter);
    }

    public void forEach(Consumer<? super E> action) {
        al.forEach(action);
    }

    /**
     * Returns a {@link Spliterator} over the elements in this set in the order
     * in which these elements were added.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
     * {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
     * {@link Spliterator#SUBSIZED}.
     *
     * <p>The spliterator provides a snapshot of the state of the set
     * when the spliterator was constructed. No synchronization is needed while
     * operating on the spliterator. The spliterator does <em>NOT</em> support
     * the {@code remove}, {@code set} or {@code add} methods.
     *
     * @return a {@code Spliterator} over the elements in this set
     * @since 1.8
     */
    public Spliterator<E> spliterator() {
        return Spliterators.spliterator
            (al.getArray(), Spliterator.IMMUTABLE | Spliterator.DISTINCT);
    }

    /**
     * Tests for equality, coping with nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null) ? o2 == null : o1.equals(o2);
    }
}
Revision:	1.56
Committed:	Thu Aug 8 15:13:34 2013 UTC (10 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.55:	+16 -0 lines
Log Message:	add javadoc for spliterator()
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8	import java.util.Collection;
9	import java.util.Collections;
10	import java.util.Set;
11	import java.util.AbstractSet;
12	import java.util.Iterator;
13	import java.util.Spliterator;
14	import java.util.Spliterators;
15	import java.util.function.Predicate;
16	import java.util.function.Consumer;
17
18	/**
19	* 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	* <ul>
22	* <li>It is best suited for applications in which set sizes generally
23	* stay small, read-only operations
24	* vastly outnumber mutative operations, and you need
25	* to prevent interference among threads during traversal.
26	* <li>It is thread-safe.
27	* <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
28	* are expensive since they usually entail copying the entire underlying
29	* array.
30	* <li>Iterators do not support the mutative {@code remove} operation.
31	* <li>Traversal via iterators is fast and cannot encounter
32	* interference from other threads. Iterators rely on
33	* unchanging snapshots of the array at the time the iterators were
34	* constructed.
35	* </ul>
36	*
37	* <p><b>Sample Usage.</b> The following code sketch uses a
38	* copy-on-write set to maintain a set of Handler objects that
39	* perform some action upon state updates.
40	*
41	* <pre> {@code
42	* class Handler { void handle(); ... }
43	*
44	* class X {
45	* private final CopyOnWriteArraySet<Handler> handlers
46	* = new CopyOnWriteArraySet<Handler>();
47	* public void addHandler(Handler h) { handlers.add(h); }
48	*
49	* private long internalState;
50	* private synchronized void changeState() { internalState = ...; }
51	*
52	* public void update() {
53	* changeState();
54	* for (Handler handler : handlers)
55	* handler.handle();
56	* }
57	* }}</pre>
58	*
59	* <p>This class is a member of the
60	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
61	* Java Collections Framework</a>.
62	*
63	* @see CopyOnWriteArrayList
64	* @since 1.5
65	* @author Doug Lea
66	* @param <E> the type of elements held in this collection
67	*/
68	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
69	implements java.io.Serializable {
70	private static final long serialVersionUID = 5457747651344034263L;
71
72	private final CopyOnWriteArrayList<E> al;
73
74	/**
75	* Creates an empty set.
76	*/
77	public CopyOnWriteArraySet() {
78	al = new CopyOnWriteArrayList<E>();
79	}
80
81	/**
82	* Creates a set containing all of the elements of the specified
83	* collection.
84	*
85	* @param c the collection of elements to initially contain
86	* @throws NullPointerException if the specified collection is null
87	*/
88	public CopyOnWriteArraySet(Collection<? extends E> c) {
89	if (c.getClass() == CopyOnWriteArraySet.class) {
90	@SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
91	(CopyOnWriteArraySet<E>)c;
92	al = new CopyOnWriteArrayList<E>(cc.al);
93	}
94	else {
95	al = new CopyOnWriteArrayList<E>();
96	al.addAllAbsent(c);
97	}
98	}
99
100	/**
101	* Returns the number of elements in this set.
102	*
103	* @return the number of elements in this set
104	*/
105	public int size() {
106	return al.size();
107	}
108
109	/**
110	* Returns {@code true} if this set contains no elements.
111	*
112	* @return {@code true} if this set contains no elements
113	*/
114	public boolean isEmpty() {
115	return al.isEmpty();
116	}
117
118	/**
119	* Returns {@code true} if this set contains the specified element.
120	* More formally, returns {@code true} if and only if this set
121	* contains an element {@code e} such that
122	* <tt>(o==null ? e==null : o.equals(e))</tt>.
123	*
124	* @param o element whose presence in this set is to be tested
125	* @return {@code true} if this set contains the specified element
126	*/
127	public boolean contains(Object o) {
128	return al.contains(o);
129	}
130
131	/**
132	* Returns an array containing all of the elements in this set.
133	* If this set makes any guarantees as to what order its elements
134	* are returned by its iterator, this method must return the
135	* elements in the same order.
136	*
137	* <p>The returned array will be "safe" in that no references to it
138	* are maintained by this set. (In other words, this method must
139	* allocate a new array even if this set is backed by an array).
140	* The caller is thus free to modify the returned array.
141	*
142	* <p>This method acts as bridge between array-based and collection-based
143	* APIs.
144	*
145	* @return an array containing all the elements in this set
146	*/
147	public Object[] toArray() {
148	return al.toArray();
149	}
150
151	/**
152	* Returns an array containing all of the elements in this set; the
153	* runtime type of the returned array is that of the specified array.
154	* If the set fits in the specified array, it is returned therein.
155	* Otherwise, a new array is allocated with the runtime type of the
156	* specified array and the size of this set.
157	*
158	* <p>If this set fits in the specified array with room to spare
159	* (i.e., the array has more elements than this set), the element in
160	* the array immediately following the end of the set is set to
161	* {@code null}. (This is useful in determining the length of this
162	* set <i>only</i> if the caller knows that this set does not contain
163	* any null elements.)
164	*
165	* <p>If this set makes any guarantees as to what order its elements
166	* are returned by its iterator, this method must return the elements
167	* in the same order.
168	*
169	* <p>Like the {@link #toArray()} method, this method acts as bridge between
170	* array-based and collection-based APIs. Further, this method allows
171	* precise control over the runtime type of the output array, and may,
172	* under certain circumstances, be used to save allocation costs.
173	*
174	* <p>Suppose {@code x} is a set known to contain only strings.
175	* The following code can be used to dump the set into a newly allocated
176	* array of {@code String}:
177	*
178	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
179	*
180	* Note that {@code toArray(new Object[0])} is identical in function to
181	* {@code toArray()}.
182	*
183	* @param a the array into which the elements of this set are to be
184	* stored, if it is big enough; otherwise, a new array of the same
185	* runtime type is allocated for this purpose.
186	* @return an array containing all the elements in this set
187	* @throws ArrayStoreException if the runtime type of the specified array
188	* is not a supertype of the runtime type of every element in this
189	* set
190	* @throws NullPointerException if the specified array is null
191	*/
192	public <T> T[] toArray(T[] a) {
193	return al.toArray(a);
194	}
195
196	/**
197	* Removes all of the elements from this set.
198	* The set will be empty after this call returns.
199	*/
200	public void clear() {
201	al.clear();
202	}
203
204	/**
205	* Removes the specified element from this set if it is present.
206	* More formally, removes an element {@code e} such that
207	* <tt>(o==null ? e==null : o.equals(e))</tt>,
208	* if this set contains such an element. Returns {@code true} if
209	* this set contained the element (or equivalently, if this set
210	* changed as a result of the call). (This set will not contain the
211	* element once the call returns.)
212	*
213	* @param o object to be removed from this set, if present
214	* @return {@code true} if this set contained the specified element
215	*/
216	public boolean remove(Object o) {
217	return al.remove(o);
218	}
219
220	/**
221	* Adds the specified element to this set if it is not already present.
222	* More formally, adds the specified element {@code e} to this set if
223	* the set contains no element {@code e2} such that
224	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
225	* If this set already contains the element, the call leaves the set
226	* unchanged and returns {@code false}.
227	*
228	* @param e element to be added to this set
229	* @return {@code true} if this set did not already contain the specified
230	* element
231	*/
232	public boolean add(E e) {
233	return al.addIfAbsent(e);
234	}
235
236	/**
237	* Returns {@code true} if this set contains all of the elements of the
238	* specified collection. If the specified collection is also a set, this
239	* method returns {@code true} if it is a <i>subset</i> of this set.
240	*
241	* @param c collection to be checked for containment in this set
242	* @return {@code true} if this set contains all of the elements of the
243	* specified collection
244	* @throws NullPointerException if the specified collection is null
245	* @see #contains(Object)
246	*/
247	public boolean containsAll(Collection<?> c) {
248	return al.containsAll(c);
249	}
250
251	/**
252	* Adds all of the elements in the specified collection to this set if
253	* they're not already present. If the specified collection is also a
254	* set, the {@code addAll} operation effectively modifies this set so
255	* that its value is the <i>union</i> of the two sets. The behavior of
256	* this operation is undefined if the specified collection is modified
257	* while the operation is in progress.
258	*
259	* @param c collection containing elements to be added to this set
260	* @return {@code true} if this set changed as a result of the call
261	* @throws NullPointerException if the specified collection is null
262	* @see #add(Object)
263	*/
264	public boolean addAll(Collection<? extends E> c) {
265	return al.addAllAbsent(c) > 0;
266	}
267
268	/**
269	* Removes from this set all of its elements that are contained in the
270	* specified collection. If the specified collection is also a set,
271	* this operation effectively modifies this set so that its value is the
272	* <i>asymmetric set difference</i> of the two sets.
273	*
274	* @param c collection containing elements to be removed from this set
275	* @return {@code true} if this set changed as a result of the call
276	* @throws ClassCastException if the class of an element of this set
277	* is incompatible with the specified collection (optional)
278	* @throws NullPointerException if this set contains a null element and the
279	* specified collection does not permit null elements (optional),
280	* or if the specified collection is null
281	* @see #remove(Object)
282	*/
283	public boolean removeAll(Collection<?> c) {
284	return al.removeAll(c);
285	}
286
287	/**
288	* Retains only the elements in this set that are contained in the
289	* specified collection. In other words, removes from this set all of
290	* its elements that are not contained in the specified collection. If
291	* the specified collection is also a set, this operation effectively
292	* modifies this set so that its value is the <i>intersection</i> of the
293	* two sets.
294	*
295	* @param c collection containing elements to be retained in this set
296	* @return {@code true} if this set changed as a result of the call
297	* @throws ClassCastException if the class of an element of this set
298	* is incompatible with the specified collection (optional)
299	* @throws NullPointerException if this set contains a null element and the
300	* specified collection does not permit null elements (optional),
301	* or if the specified collection is null
302	* @see #remove(Object)
303	*/
304	public boolean retainAll(Collection<?> c) {
305	return al.retainAll(c);
306	}
307
308	/**
309	* Returns an iterator over the elements contained in this set
310	* in the order in which these elements were added.
311	*
312	* <p>The returned iterator provides a snapshot of the state of the set
313	* when the iterator was constructed. No synchronization is needed while
314	* traversing the iterator. The iterator does <em>NOT</em> support the
315	* {@code remove} method.
316	*
317	* @return an iterator over the elements in this set
318	*/
319	public Iterator<E> iterator() {
320	return al.iterator();
321	}
322
323	/**
324	* Compares the specified object with this set for equality.
325	* Returns {@code true} if the specified object is the same object
326	* as this object, or if it is also a {@link Set} and the elements
327	* returned by an {@linkplain Set#iterator() iterator} over the
328	* specified set are the same as the elements returned by an
329	* iterator over this set. More formally, the two iterators are
330	* considered to return the same elements if they return the same
331	* number of elements and for every element {@code e1} returned by
332	* the iterator over the specified set, there is an element
333	* {@code e2} returned by the iterator over this set such that
334	* {@code (e1==null ? e2==null : e1.equals(e2))}.
335	*
336	* @param o object to be compared for equality with this set
337	* @return {@code true} if the specified object is equal to this set
338	*/
339	public boolean equals(Object o) {
340	if (o == this)
341	return true;
342	if (!(o instanceof Set))
343	return false;
344	Set<?> set = (Set<?>)(o);
345	Iterator<?> it = set.iterator();
346
347	// Uses O(n^2) algorithm that is only appropriate
348	// for small sets, which CopyOnWriteArraySets should be.
349
350	// Use a single snapshot of underlying array
351	Object[] elements = al.getArray();
352	int len = elements.length;
353	// Mark matched elements to avoid re-checking
354	boolean[] matched = new boolean[len];
355	int k = 0;
356	outer: while (it.hasNext()) {
357	if (++k > len)
358	return false;
359	Object x = it.next();
360	for (int i = 0; i < len; ++i) {
361	if (!matched[i] && eq(x, elements[i])) {
362	matched[i] = true;
363	continue outer;
364	}
365	}
366	return false;
367	}
368	return k == len;
369	}
370
371	public boolean removeIf(Predicate<? super E> filter) {
372	return al.removeIf(filter);
373	}
374
375	public void forEach(Consumer<? super E> action) {
376	al.forEach(action);
377	}
378
379	/**
380	* Returns a {@link Spliterator} over the elements in this set in the order
381	* in which these elements were added.
382	*
383	* <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
384	* {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
385	* {@link Spliterator#SUBSIZED}.
386	*
387	* <p>The spliterator provides a snapshot of the state of the set
388	* when the spliterator was constructed. No synchronization is needed while
389	* operating on the spliterator. The spliterator does <em>NOT</em> support
390	* the {@code remove}, {@code set} or {@code add} methods.
391	*
392	* @return a {@code Spliterator} over the elements in this set
393	* @since 1.8
394	*/
395	public Spliterator<E> spliterator() {
396	return Spliterators.spliterator
397	(al.getArray(), Spliterator.IMMUTABLE \| Spliterator.DISTINCT);
398	}
399
400	/**
401	* Tests for equality, coping with nulls.
402	*/
403	private static boolean eq(Object o1, Object o2) {
404	return (o1 == null) ? o2 == null : o1.equals(o2);
405	}
406	}