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.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import java.util.function.Predicate;

/**
 * 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<>();
 *   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 set
 */
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 {@code Objects.equals(o, e)}.
     *
     * @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
     * {@code Objects.equals(o, e)}, 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
     * {@code Objects.equals(e, e2)}.
     * 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 Objects.equals(e1, 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:	1.63
Committed:	Fri Jan 2 07:42:41 2015 UTC (9 years, 5 months ago) by jsr166
Branch:	MAIN
Changes since 1.62:	+1 -1 lines
Log Message:	remove redundant parens
#	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	jsr166	1.61
9			import java.util.AbstractSet;
10	dl	1.45	import java.util.Collection;
11	jsr166	1.61	import java.util.Iterator;
12	dl	1.45	import java.util.Set;
13			import java.util.Spliterator;
14	dl	1.50	import java.util.Spliterators;
15	jsr166	1.61	import java.util.function.Consumer;
16	dl	1.54	import java.util.function.Predicate;
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	jsr166	1.57	* = new CopyOnWriteArraySet<>();
47	jsr166	1.37	* 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	jsr166	1.60	* @param <E> the type of elements held in this set
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	dl	1.54	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	tim	1.1	}
99
100	jsr166	1.26	/**
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	jsr166	1.36	return al.size();
107	jsr166	1.26	}
108
109			/**
110	jsr166	1.44	* Returns {@code true} if this set contains no elements.
111	jsr166	1.26	*
112	jsr166	1.44	* @return {@code true} if this set contains no elements
113	jsr166	1.26	*/
114			public boolean isEmpty() {
115	jsr166	1.36	return al.isEmpty();
116	jsr166	1.26	}
117
118			/**
119	jsr166	1.44	* Returns {@code true} if this set contains the specified element.
120			* More formally, returns {@code true} if and only if this set
121	jsr166	1.58	* contains an element {@code e} such that {@code Objects.equals(o, e)}.
122	jsr166	1.26	*
123			* @param o element whose presence in this set is to be tested
124	jsr166	1.44	* @return {@code true} if this set contains the specified element
125	jsr166	1.26	*/
126			public boolean contains(Object o) {
127	jsr166	1.36	return al.contains(o);
128	jsr166	1.26	}
129
130			/**
131			* Returns an array containing all of the elements in this set.
132			* If this set makes any guarantees as to what order its elements
133			* are returned by its iterator, this method must return the
134			* elements in the same order.
135			*
136			* <p>The returned array will be "safe" in that no references to it
137			* are maintained by this set. (In other words, this method must
138			* allocate a new array even if this set is backed by an array).
139			* The caller is thus free to modify the returned array.
140			*
141			* <p>This method acts as bridge between array-based and collection-based
142			* APIs.
143			*
144			* @return an array containing all the elements in this set
145			*/
146			public Object[] toArray() {
147	jsr166	1.36	return al.toArray();
148	jsr166	1.26	}
149
150			/**
151			* Returns an array containing all of the elements in this set; the
152			* runtime type of the returned array is that of the specified array.
153			* If the set fits in the specified array, it is returned therein.
154			* Otherwise, a new array is allocated with the runtime type of the
155			* specified array and the size of this set.
156			*
157			* <p>If this set fits in the specified array with room to spare
158			* (i.e., the array has more elements than this set), the element in
159			* the array immediately following the end of the set is set to
160	jsr166	1.44	* {@code null}. (This is useful in determining the length of this
161	jsr166	1.26	* set <i>only</i> if the caller knows that this set does not contain
162			* any null elements.)
163			*
164			* <p>If this set makes any guarantees as to what order its elements
165			* are returned by its iterator, this method must return the elements
166			* in the same order.
167			*
168			* <p>Like the {@link #toArray()} method, this method acts as bridge between
169			* array-based and collection-based APIs. Further, this method allows
170			* precise control over the runtime type of the output array, and may,
171			* under certain circumstances, be used to save allocation costs.
172			*
173	jsr166	1.44	* <p>Suppose {@code x} is a set known to contain only strings.
174	jsr166	1.26	* The following code can be used to dump the set into a newly allocated
175	jsr166	1.44	* array of {@code String}:
176	jsr166	1.26	*
177	jsr166	1.40	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
178	jsr166	1.26	*
179	jsr166	1.44	* Note that {@code toArray(new Object[0])} is identical in function to
180			* {@code toArray()}.
181	jsr166	1.26	*
182			* @param a the array into which the elements of this set are to be
183			* stored, if it is big enough; otherwise, a new array of the same
184			* runtime type is allocated for this purpose.
185			* @return an array containing all the elements in this set
186			* @throws ArrayStoreException if the runtime type of the specified array
187			* is not a supertype of the runtime type of every element in this
188			* set
189			* @throws NullPointerException if the specified array is null
190			*/
191			public <T> T[] toArray(T[] a) {
192	jsr166	1.36	return al.toArray(a);
193	jsr166	1.26	}
194
195			/**
196			* Removes all of the elements from this set.
197	jsr166	1.27	* The set will be empty after this call returns.
198	jsr166	1.26	*/
199			public void clear() {
200			al.clear();
201			}
202
203			/**
204			* Removes the specified element from this set if it is present.
205	jsr166	1.44	* More formally, removes an element {@code e} such that
206	jsr166	1.58	* {@code Objects.equals(o, e)}, if this set contains such an element.
207			* Returns {@code true} if this set contained the element (or
208			* equivalently, if this set changed as a result of the call).
209			* (This set will not contain the element once the call returns.)
210	jsr166	1.26	*
211			* @param o object to be removed from this set, if present
212	jsr166	1.44	* @return {@code true} if this set contained the specified element
213	jsr166	1.26	*/
214			public boolean remove(Object o) {
215	jsr166	1.36	return al.remove(o);
216	jsr166	1.26	}
217
218			/**
219			* Adds the specified element to this set if it is not already present.
220	jsr166	1.44	* More formally, adds the specified element {@code e} to this set if
221			* the set contains no element {@code e2} such that
222	jsr166	1.58	* {@code Objects.equals(e, e2)}.
223	jsr166	1.28	* If this set already contains the element, the call leaves the set
224	jsr166	1.44	* unchanged and returns {@code false}.
225	jsr166	1.26	*
226			* @param e element to be added to this set
227	jsr166	1.44	* @return {@code true} if this set did not already contain the specified
228	jsr166	1.26	* element
229			*/
230			public boolean add(E e) {
231	jsr166	1.36	return al.addIfAbsent(e);
232	jsr166	1.26	}
233	tim	1.1
234	jsr166	1.26	/**
235	jsr166	1.44	* Returns {@code true} if this set contains all of the elements of the
236	jsr166	1.26	* specified collection. If the specified collection is also a set, this
237	jsr166	1.44	* method returns {@code true} if it is a <i>subset</i> of this set.
238	jsr166	1.26	*
239			* @param c collection to be checked for containment in this set
240	jsr166	1.44	* @return {@code true} if this set contains all of the elements of the
241	jsr166	1.36	* specified collection
242	jsr166	1.26	* @throws NullPointerException if the specified collection is null
243			* @see #contains(Object)
244			*/
245			public boolean containsAll(Collection<?> c) {
246	jsr166	1.36	return al.containsAll(c);
247	jsr166	1.26	}
248
249			/**
250			* Adds all of the elements in the specified collection to this set if
251			* they're not already present. If the specified collection is also a
252	jsr166	1.44	* set, the {@code addAll} operation effectively modifies this set so
253	jsr166	1.26	* that its value is the <i>union</i> of the two sets. The behavior of
254	jsr166	1.28	* this operation is undefined if the specified collection is modified
255	jsr166	1.26	* while the operation is in progress.
256			*
257			* @param c collection containing elements to be added to this set
258	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
259	jsr166	1.26	* @throws NullPointerException if the specified collection is null
260			* @see #add(Object)
261			*/
262			public boolean addAll(Collection<? extends E> c) {
263	dl	1.52	return al.addAllAbsent(c) > 0;
264	jsr166	1.26	}
265
266			/**
267			* Removes from this set all of its elements that are contained in the
268			* specified collection. If the specified collection is also a set,
269			* this operation effectively modifies this set so that its value is the
270			* <i>asymmetric set difference</i> of the two sets.
271			*
272			* @param c collection containing elements to be removed from this set
273	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
274	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
275			* is incompatible with the specified collection (optional)
276			* @throws NullPointerException if this set contains a null element and the
277			* specified collection does not permit null elements (optional),
278			* or if the specified collection is null
279			* @see #remove(Object)
280			*/
281			public boolean removeAll(Collection<?> c) {
282	jsr166	1.36	return al.removeAll(c);
283	jsr166	1.26	}
284
285			/**
286			* Retains only the elements in this set that are contained in the
287			* specified collection. In other words, removes from this set all of
288			* its elements that are not contained in the specified collection. If
289			* the specified collection is also a set, this operation effectively
290			* modifies this set so that its value is the <i>intersection</i> of the
291			* two sets.
292			*
293			* @param c collection containing elements to be retained in this set
294	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
295	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
296			* is incompatible with the specified collection (optional)
297			* @throws NullPointerException if this set contains a null element and the
298			* specified collection does not permit null elements (optional),
299			* or if the specified collection is null
300			* @see #remove(Object)
301			*/
302			public boolean retainAll(Collection<?> c) {
303	jsr166	1.36	return al.retainAll(c);
304	jsr166	1.26	}
305	tim	1.1
306	dl	1.20	/**
307	jsr166	1.24	* Returns an iterator over the elements contained in this set
308	dl	1.20	* in the order in which these elements were added.
309	jsr166	1.26	*
310			* <p>The returned iterator provides a snapshot of the state of the set
311			* when the iterator was constructed. No synchronization is needed while
312			* traversing the iterator. The iterator does <em>NOT</em> support the
313	jsr166	1.44	* {@code remove} method.
314	jsr166	1.26	*
315			* @return an iterator over the elements in this set
316	dl	1.20	*/
317	jsr166	1.26	public Iterator<E> iterator() {
318	jsr166	1.36	return al.iterator();
319	jsr166	1.26	}
320	dl	1.20
321	dl	1.30	/**
322			* Compares the specified object with this set for equality.
323	jsr166	1.33	* Returns {@code true} if the specified object is the same object
324			* as this object, or if it is also a {@link Set} and the elements
325	jsr166	1.47	* returned by an {@linkplain Set#iterator() iterator} over the
326	jsr166	1.33	* specified set are the same as the elements returned by an
327			* iterator over this set. More formally, the two iterators are
328			* considered to return the same elements if they return the same
329			* number of elements and for every element {@code e1} returned by
330			* the iterator over the specified set, there is an element
331			* {@code e2} returned by the iterator over this set such that
332	jsr166	1.59	* {@code Objects.equals(e1, e2)}.
333	dl	1.30	*
334			* @param o object to be compared for equality with this set
335	jsr166	1.33	* @return {@code true} if the specified object is equal to this set
336	dl	1.30	*/
337			public boolean equals(Object o) {
338			if (o == this)
339			return true;
340			if (!(o instanceof Set))
341			return false;
342	jsr166	1.63	Set<?> set = (Set<?>)o;
343	jsr166	1.36	Iterator<?> it = set.iterator();
344	dl	1.30
345			// Uses O(n^2) algorithm that is only appropriate
346			// for small sets, which CopyOnWriteArraySets should be.
347
348			// Use a single snapshot of underlying array
349	jsr166	1.36	Object[] elements = al.getArray();
350			int len = elements.length;
351	dl	1.30	// Mark matched elements to avoid re-checking
352			boolean[] matched = new boolean[len];
353			int k = 0;
354	jsr166	1.33	outer: while (it.hasNext()) {
355	dl	1.30	if (++k > len)
356			return false;
357	jsr166	1.33	Object x = it.next();
358	dl	1.30	for (int i = 0; i < len; ++i) {
359			if (!matched[i] && eq(x, elements[i])) {
360			matched[i] = true;
361	jsr166	1.36	continue outer;
362	dl	1.30	}
363			}
364	jsr166	1.36	return false;
365	dl	1.30	}
366			return k == len;
367			}
368	jsr166	1.32
369	dl	1.54	public boolean removeIf(Predicate<? super E> filter) {
370			return al.removeIf(filter);
371			}
372
373			public void forEach(Consumer<? super E> action) {
374			al.forEach(action);
375			}
376
377	jsr166	1.56	/**
378			* Returns a {@link Spliterator} over the elements in this set in the order
379			* in which these elements were added.
380			*
381			* <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
382			* {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
383			* {@link Spliterator#SUBSIZED}.
384			*
385			* <p>The spliterator provides a snapshot of the state of the set
386			* when the spliterator was constructed. No synchronization is needed while
387			* operating on the spliterator. The spliterator does <em>NOT</em> support
388			* the {@code remove}, {@code set} or {@code add} methods.
389			*
390			* @return a {@code Spliterator} over the elements in this set
391			* @since 1.8
392			*/
393	dl	1.51	public Spliterator<E> spliterator() {
394	dl	1.50	return Spliterators.spliterator
395	dl	1.55	(al.getArray(), Spliterator.IMMUTABLE \| Spliterator.DISTINCT);
396	dl	1.48	}
397
398	dl	1.30	/**
399	jsr166	1.41	* Tests for equality, coping with nulls.
400	dl	1.30	*/
401			private static boolean eq(Object o1, Object o2) {
402	jsr166	1.39	return (o1 == null) ? o2 == null : o1.equals(o2);
403	dl	1.30	}
404	tim	1.1	}