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

/**
 * A {@link 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}/java.base/java/util/package-summary.html#CollectionsFramework">
 * 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 (c instanceof Set)
            ? compareSets(al.getArray(), (Set<?>) c) >= 0
            : al.containsAll(c);
    }

    /**
     * Tells whether the objects in snapshot (regarded as a set) are a
     * superset of the given set.
     *
     * @return -1 if snapshot is not a superset, 0 if the two sets
     * contain precisely the same elements, and 1 if snapshot is a
     * proper superset of the given set
     */
    private static int compareSets(Object[] snapshot, Set<?> set) {
        // Uses O(n^2) algorithm, that is only appropriate for small
        // sets, which CopyOnWriteArraySets should be.
        //
        // Optimize up to O(n) if the two sets share a long common prefix,
        // as might happen if one set was created as a copy of the other set.

        final int len = snapshot.length;
        // Mark matched elements to avoid re-checking
        final boolean[] matched = new boolean[len];

        // j is the largest int with matched[i] true for { i | 0 <= i < j }
        int j = 0;
        outer: for (Object x : set) {
            for (int i = j; i < len; i++) {
                if (!matched[i] && Objects.equals(x, snapshot[i])) {
                    matched[i] = true;
                    if (i == j)
                        do { j++; } while (j < len && matched[j]);
                    continue outer;
                }
            }
            return -1;
        }
        return (j == len) ? 0 : 1;
    }

    /**
     * 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
     * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements
     * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
     *         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
     * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements
     * (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
     *         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) {
        return (o == this)
            || ((o instanceof Set)
                && compareSets(al.getArray(), (Set<?>) o) == 0);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     */
    public boolean removeIf(Predicate<? super E> filter) {
        return al.removeIf(filter);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     */
    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.
     *
     * @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);
    }
}
Revision:	1.75
Committed:	Fri Nov 27 17:41:59 2020 UTC (3 years, 6 months ago) by dl
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.74:	+1 -1 lines
Log Message:	Incorporate snippets code improvements from Pavel Rappo
#	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	jsr166	1.65	import java.util.Objects;
13	dl	1.45	import java.util.Set;
14			import java.util.Spliterator;
15	dl	1.50	import java.util.Spliterators;
16	jsr166	1.61	import java.util.function.Consumer;
17	dl	1.54	import java.util.function.Predicate;
18	tim	1.1
19			/**
20	jsr166	1.72	* A {@link Set} that uses an internal {@link CopyOnWriteArrayList}
21	jsr166	1.26	* for all of its operations. Thus, it shares the same basic properties:
22	tim	1.1	* <ul>
23	dholmes	1.7	* <li>It is best suited for applications in which set sizes generally
24	tim	1.1	* stay small, read-only operations
25			* vastly outnumber mutative operations, and you need
26			* to prevent interference among threads during traversal.
27	dl	1.16	* <li>It is thread-safe.
28	jsr166	1.44	* <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
29	jsr166	1.26	* are expensive since they usually entail copying the entire underlying
30			* array.
31	jsr166	1.44	* <li>Iterators do not support the mutative {@code remove} operation.
32	dl	1.18	* <li>Traversal via iterators is fast and cannot encounter
33	tim	1.1	* interference from other threads. Iterators rely on
34			* unchanging snapshots of the array at the time the iterators were
35	jsr166	1.26	* constructed.
36	tim	1.1	* </ul>
37	dl	1.18	*
38	jsr166	1.42	* <p><b>Sample Usage.</b> The following code sketch uses a
39	jsr166	1.21	* copy-on-write set to maintain a set of Handler objects that
40			* perform some action upon state updates.
41	dl	1.18	*
42	jsr166	1.64	* <pre> {@code
43	dl	1.75	* class Handler { void handle() { ... } }
44	tim	1.1	*
45			* class X {
46	jsr166	1.37	* private final CopyOnWriteArraySet<Handler> handlers
47	jsr166	1.57	* = new CopyOnWriteArraySet<>();
48	jsr166	1.37	* public void addHandler(Handler h) { handlers.add(h); }
49	tim	1.1	*
50	jsr166	1.37	* private long internalState;
51			* private synchronized void changeState() { internalState = ...; }
52	tim	1.1	*
53	jsr166	1.37	* public void update() {
54			* changeState();
55			* for (Handler handler : handlers)
56	jsr166	1.43	* handler.handle();
57	jsr166	1.37	* }
58			* }}</pre>
59	dl	1.14	*
60			* <p>This class is a member of the
61	jsr166	1.74	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
62	dl	1.14	* Java Collections Framework</a>.
63			*
64	dl	1.16	* @see CopyOnWriteArrayList
65	dl	1.4	* @since 1.5
66			* @author Doug Lea
67	jsr166	1.60	* @param <E> the type of elements held in this set
68	dl	1.4	*/
69	tim	1.1	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
70	dl	1.18	implements java.io.Serializable {
71	dl	1.8	private static final long serialVersionUID = 5457747651344034263L;
72	tim	1.1
73			private final CopyOnWriteArrayList<E> al;
74
75			/**
76	dl	1.15	* Creates an empty set.
77	tim	1.1	*/
78			public CopyOnWriteArraySet() {
79			al = new CopyOnWriteArrayList<E>();
80			}
81
82			/**
83	dl	1.15	* Creates a set containing all of the elements of the specified
84	jsr166	1.23	* collection.
85	jsr166	1.25	*
86	jsr166	1.23	* @param c the collection of elements to initially contain
87			* @throws NullPointerException if the specified collection is null
88	tim	1.1	*/
89	tim	1.12	public CopyOnWriteArraySet(Collection<? extends E> c) {
90	dl	1.54	if (c.getClass() == CopyOnWriteArraySet.class) {
91			@SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
92			(CopyOnWriteArraySet<E>)c;
93			al = new CopyOnWriteArrayList<E>(cc.al);
94			}
95			else {
96			al = new CopyOnWriteArrayList<E>();
97			al.addAllAbsent(c);
98			}
99	tim	1.1	}
100
101	jsr166	1.26	/**
102			* Returns the number of elements in this set.
103			*
104			* @return the number of elements in this set
105			*/
106			public int size() {
107	jsr166	1.36	return al.size();
108	jsr166	1.26	}
109
110			/**
111	jsr166	1.44	* Returns {@code true} if this set contains no elements.
112	jsr166	1.26	*
113	jsr166	1.44	* @return {@code true} if this set contains no elements
114	jsr166	1.26	*/
115			public boolean isEmpty() {
116	jsr166	1.36	return al.isEmpty();
117	jsr166	1.26	}
118
119			/**
120	jsr166	1.44	* Returns {@code true} if this set contains the specified element.
121			* More formally, returns {@code true} if and only if this set
122	jsr166	1.58	* contains an element {@code e} such that {@code Objects.equals(o, e)}.
123	jsr166	1.26	*
124			* @param o element whose presence in this set is to be tested
125	jsr166	1.44	* @return {@code true} if this set contains the specified element
126	jsr166	1.26	*/
127			public boolean contains(Object o) {
128	jsr166	1.36	return al.contains(o);
129	jsr166	1.26	}
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	jsr166	1.36	return al.toArray();
149	jsr166	1.26	}
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	jsr166	1.44	* {@code null}. (This is useful in determining the length of this
162	jsr166	1.26	* 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	jsr166	1.44	* <p>Suppose {@code x} is a set known to contain only strings.
175	jsr166	1.26	* The following code can be used to dump the set into a newly allocated
176	jsr166	1.44	* array of {@code String}:
177	jsr166	1.26	*
178	jsr166	1.64	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
179	jsr166	1.26	*
180	jsr166	1.44	* Note that {@code toArray(new Object[0])} is identical in function to
181			* {@code toArray()}.
182	jsr166	1.26	*
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	jsr166	1.36	return al.toArray(a);
194	jsr166	1.26	}
195
196			/**
197			* Removes all of the elements from this set.
198	jsr166	1.27	* The set will be empty after this call returns.
199	jsr166	1.26	*/
200			public void clear() {
201			al.clear();
202			}
203
204			/**
205			* Removes the specified element from this set if it is present.
206	jsr166	1.44	* More formally, removes an element {@code e} such that
207	jsr166	1.58	* {@code Objects.equals(o, e)}, if this set contains such an element.
208			* Returns {@code true} if this set contained the element (or
209			* equivalently, if this set changed as a result of the call).
210			* (This set will not contain the element once the call returns.)
211	jsr166	1.26	*
212			* @param o object to be removed from this set, if present
213	jsr166	1.44	* @return {@code true} if this set contained the specified element
214	jsr166	1.26	*/
215			public boolean remove(Object o) {
216	jsr166	1.36	return al.remove(o);
217	jsr166	1.26	}
218
219			/**
220			* Adds the specified element to this set if it is not already present.
221	jsr166	1.44	* More formally, adds the specified element {@code e} to this set if
222			* the set contains no element {@code e2} such that
223	jsr166	1.58	* {@code Objects.equals(e, e2)}.
224	jsr166	1.28	* If this set already contains the element, the call leaves the set
225	jsr166	1.44	* unchanged and returns {@code false}.
226	jsr166	1.26	*
227			* @param e element to be added to this set
228	jsr166	1.44	* @return {@code true} if this set did not already contain the specified
229	jsr166	1.26	* element
230			*/
231			public boolean add(E e) {
232	jsr166	1.36	return al.addIfAbsent(e);
233	jsr166	1.26	}
234	tim	1.1
235	jsr166	1.26	/**
236	jsr166	1.44	* Returns {@code true} if this set contains all of the elements of the
237	jsr166	1.26	* specified collection. If the specified collection is also a set, this
238	jsr166	1.44	* method returns {@code true} if it is a <i>subset</i> of this set.
239	jsr166	1.26	*
240			* @param c collection to be checked for containment in this set
241	jsr166	1.44	* @return {@code true} if this set contains all of the elements of the
242	jsr166	1.36	* specified collection
243	jsr166	1.26	* @throws NullPointerException if the specified collection is null
244			* @see #contains(Object)
245			*/
246			public boolean containsAll(Collection<?> c) {
247	jsr166	1.66	return (c instanceof Set)
248			? compareSets(al.getArray(), (Set<?>) c) >= 0
249			: al.containsAll(c);
250			}
251
252			/**
253			* Tells whether the objects in snapshot (regarded as a set) are a
254			* superset of the given set.
255			*
256			* @return -1 if snapshot is not a superset, 0 if the two sets
257			* contain precisely the same elements, and 1 if snapshot is a
258			* proper superset of the given set
259			*/
260			private static int compareSets(Object[] snapshot, Set<?> set) {
261			// Uses O(n^2) algorithm, that is only appropriate for small
262			// sets, which CopyOnWriteArraySets should be.
263			//
264			// Optimize up to O(n) if the two sets share a long common prefix,
265			// as might happen if one set was created as a copy of the other set.
266
267			final int len = snapshot.length;
268			// Mark matched elements to avoid re-checking
269			final boolean[] matched = new boolean[len];
270
271			// j is the largest int with matched[i] true for { i \| 0 <= i < j }
272			int j = 0;
273			outer: for (Object x : set) {
274			for (int i = j; i < len; i++) {
275			if (!matched[i] && Objects.equals(x, snapshot[i])) {
276			matched[i] = true;
277			if (i == j)
278			do { j++; } while (j < len && matched[j]);
279			continue outer;
280			}
281			}
282			return -1;
283			}
284			return (j == len) ? 0 : 1;
285	jsr166	1.26	}
286
287			/**
288			* Adds all of the elements in the specified collection to this set if
289			* they're not already present. If the specified collection is also a
290	jsr166	1.44	* set, the {@code addAll} operation effectively modifies this set so
291	jsr166	1.26	* that its value is the <i>union</i> of the two sets. The behavior of
292	jsr166	1.28	* this operation is undefined if the specified collection is modified
293	jsr166	1.26	* while the operation is in progress.
294			*
295			* @param c collection containing elements to be added to this set
296	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
297	jsr166	1.26	* @throws NullPointerException if the specified collection is null
298			* @see #add(Object)
299			*/
300			public boolean addAll(Collection<? extends E> c) {
301	dl	1.52	return al.addAllAbsent(c) > 0;
302	jsr166	1.26	}
303
304			/**
305			* Removes from this set all of its elements that are contained in the
306			* specified collection. If the specified collection is also a set,
307			* this operation effectively modifies this set so that its value is the
308			* <i>asymmetric set difference</i> of the two sets.
309			*
310			* @param c collection containing elements to be removed from this set
311	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
312	jsr166	1.26	* @throws ClassCastException if the class of an element of this set
313	jsr166	1.67	* is incompatible with the specified collection
314	jsr166	1.74	* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
315	jsr166	1.26	* @throws NullPointerException if this set contains a null element and the
316	jsr166	1.67	* specified collection does not permit null elements
317	jsr166	1.74	* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
318	jsr166	1.26	* or if the specified collection is null
319			* @see #remove(Object)
320			*/
321			public boolean removeAll(Collection<?> c) {
322	jsr166	1.36	return al.removeAll(c);
323	jsr166	1.26	}
324
325			/**
326			* Retains only the elements in this set that are contained in the
327			* specified collection. In other words, removes from this set all of
328			* its elements that are not contained in the specified collection. If
329			* the specified collection is also a set, this operation effectively
330			* modifies this set so that its value is the <i>intersection</i> of the
331			* two sets.
332			*
333			* @param c collection containing elements to be retained in this set
334	jsr166	1.44	* @return {@code true} if this set changed as a result of the call
335	jsr166	1.69	* @throws ClassCastException if the class of an element of this set
336			* is incompatible with the specified collection
337	jsr166	1.74	* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>)
338	jsr166	1.69	* @throws NullPointerException if this set contains a null element and the
339			* specified collection does not permit null elements
340	jsr166	1.74	* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>),
341	jsr166	1.26	* or if the specified collection is null
342			* @see #remove(Object)
343			*/
344			public boolean retainAll(Collection<?> c) {
345	jsr166	1.36	return al.retainAll(c);
346	jsr166	1.26	}
347	tim	1.1
348	dl	1.20	/**
349	jsr166	1.24	* Returns an iterator over the elements contained in this set
350	dl	1.20	* in the order in which these elements were added.
351	jsr166	1.26	*
352			* <p>The returned iterator provides a snapshot of the state of the set
353			* when the iterator was constructed. No synchronization is needed while
354			* traversing the iterator. The iterator does <em>NOT</em> support the
355	jsr166	1.44	* {@code remove} method.
356	jsr166	1.26	*
357			* @return an iterator over the elements in this set
358	dl	1.20	*/
359	jsr166	1.26	public Iterator<E> iterator() {
360	jsr166	1.36	return al.iterator();
361	jsr166	1.26	}
362	dl	1.20
363	dl	1.30	/**
364			* Compares the specified object with this set for equality.
365	jsr166	1.33	* Returns {@code true} if the specified object is the same object
366			* as this object, or if it is also a {@link Set} and the elements
367	jsr166	1.47	* returned by an {@linkplain Set#iterator() iterator} over the
368	jsr166	1.33	* specified set are the same as the elements returned by an
369			* iterator over this set. More formally, the two iterators are
370			* considered to return the same elements if they return the same
371			* number of elements and for every element {@code e1} returned by
372			* the iterator over the specified set, there is an element
373			* {@code e2} returned by the iterator over this set such that
374	jsr166	1.59	* {@code Objects.equals(e1, e2)}.
375	dl	1.30	*
376			* @param o object to be compared for equality with this set
377	jsr166	1.33	* @return {@code true} if the specified object is equal to this set
378	dl	1.30	*/
379			public boolean equals(Object o) {
380	jsr166	1.66	return (o == this)
381			\|\| ((o instanceof Set)
382			&& compareSets(al.getArray(), (Set<?>) o) == 0);
383	dl	1.30	}
384	jsr166	1.32
385	jsr166	1.71	/**
386			* @throws NullPointerException {@inheritDoc}
387			*/
388	dl	1.54	public boolean removeIf(Predicate<? super E> filter) {
389			return al.removeIf(filter);
390			}
391
392	jsr166	1.71	/**
393			* @throws NullPointerException {@inheritDoc}
394			*/
395	dl	1.54	public void forEach(Consumer<? super E> action) {
396			al.forEach(action);
397			}
398
399	jsr166	1.56	/**
400			* Returns a {@link Spliterator} over the elements in this set in the order
401			* in which these elements were added.
402			*
403			* <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
404			* {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
405			* {@link Spliterator#SUBSIZED}.
406			*
407			* <p>The spliterator provides a snapshot of the state of the set
408			* when the spliterator was constructed. No synchronization is needed while
409	jsr166	1.68	* operating on the spliterator.
410	jsr166	1.56	*
411			* @return a {@code Spliterator} over the elements in this set
412			* @since 1.8
413			*/
414	dl	1.51	public Spliterator<E> spliterator() {
415	dl	1.50	return Spliterators.spliterator
416	dl	1.55	(al.getArray(), Spliterator.IMMUTABLE \| Spliterator.DISTINCT);
417	dl	1.48	}
418	tim	1.1	}