util/concurrent/CopyOnWriteArraySet.java

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

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

/**
 * A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
 * for all of its operations.  Thus, it shares the same basic properties:
 * <ul>
 *  <li>It is best suited for applications in which set sizes generally
 *       stay small, read-only operations
 *       vastly outnumber mutative operations, and you need
 *       to prevent interference among threads during traversal.
 *  <li>It is thread-safe.
 *  <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
 *      are expensive since they usually entail copying the entire underlying
 *      array.
 *  <li>Iterators do not support the mutative {@code remove} operation.
 *  <li>Traversal via iterators is fast and cannot encounter
 *      interference from other threads. Iterators rely on
 *      unchanging snapshots of the array at the time the iterators were
 *      constructed.
 * </ul>
 *
 * <p><b>Sample Usage.</b> The following code sketch uses a
 * copy-on-write set to maintain a set of Handler objects that
 * perform some action upon state updates.
 *
 *  <pre> {@code
 * class Handler { void handle(); ... }
 *
 * class X {
 *   private final CopyOnWriteArraySet<Handler> handlers
 *     = new CopyOnWriteArraySet<Handler>();
 *   public void addHandler(Handler h) { handlers.add(h); }
 *
 *   private long internalState;
 *   private synchronized void changeState() { internalState = ...; }
 *
 *   public void update() {
 *     changeState();
 *     for (Handler handler : handlers)
 *       handler.handle();
 *   }
 * }}</pre>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @see CopyOnWriteArrayList
 * @since 1.5
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
        implements java.io.Serializable {
    private static final long serialVersionUID = 5457747651344034263L;

    private final CopyOnWriteArrayList<E> al;

    /**
     * Creates an empty set.
     */
    public CopyOnWriteArraySet() {
        al = new CopyOnWriteArrayList<E>();
    }

    /**
     * Creates a set containing all of the elements of the specified
     * collection.
     *
     * @param c the collection of elements to initially contain
     * @throws NullPointerException if the specified collection is null
     */
    public CopyOnWriteArraySet(Collection<? extends E> c) {
        al = new CopyOnWriteArrayList<E>();
        al.addAllAbsent(c);
    }

    /**
     * Returns the number of elements in this set.
     *
     * @return the number of elements in this set
     */
    public int size() {
        return al.size();
    }

    /**
     * Returns {@code true} if this set contains no elements.
     *
     * @return {@code true} if this set contains no elements
     */
    public boolean isEmpty() {
        return al.isEmpty();
    }

    /**
     * Returns {@code true} if this set contains the specified element.
     * More formally, returns {@code true} if and only if this set
     * contains an element {@code e} such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o element whose presence in this set is to be tested
     * @return {@code true} if this set contains the specified element
     */
    public boolean contains(Object o) {
        return al.contains(o);
    }

    /**
     * Returns an array containing all of the elements in this set.
     * If this set makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the
     * elements in the same order.
     *
     * <p>The returned array will be "safe" in that no references to it
     * are maintained by this set.  (In other words, this method must
     * allocate a new array even if this set is backed by an array).
     * The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all the elements in this set
     */
    public Object[] toArray() {
        return al.toArray();
    }

    /**
     * Returns an array containing all of the elements in this set; the
     * runtime type of the returned array is that of the specified array.
     * If the set fits in the specified array, it is returned therein.
     * Otherwise, a new array is allocated with the runtime type of the
     * specified array and the size of this set.
     *
     * <p>If this set fits in the specified array with room to spare
     * (i.e., the array has more elements than this set), the element in
     * the array immediately following the end of the set is set to
     * {@code null}.  (This is useful in determining the length of this
     * set <i>only</i> if the caller knows that this set does not contain
     * any null elements.)
     *
     * <p>If this set makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the elements
     * in the same order.
     *
     * <p>Like the {@link #toArray()} method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>Suppose {@code x} is a set known to contain only strings.
     * The following code can be used to dump the set into a newly allocated
     * array of {@code String}:
     *
     *  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
     *
     * Note that {@code toArray(new Object[0])} is identical in function to
     * {@code toArray()}.
     *
     * @param a the array into which the elements of this set are to be
     *        stored, if it is big enough; otherwise, a new array of the same
     *        runtime type is allocated for this purpose.
     * @return an array containing all the elements in this set
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in this
     *         set
     * @throws NullPointerException if the specified array is null
     */
    public <T> T[] toArray(T[] a) {
        return al.toArray(a);
    }

    /**
     * Removes all of the elements from this set.
     * The set will be empty after this call returns.
     */
    public void clear() {
        al.clear();
    }

    /**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element {@code e} such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
     * if this set contains such an element.  Returns {@code true} if
     * this set contained the element (or equivalently, if this set
     * changed as a result of the call).  (This set will not contain the
     * element once the call returns.)
     *
     * @param o object to be removed from this set, if present
     * @return {@code true} if this set contained the specified element
     */
    public boolean remove(Object o) {
        return al.remove(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     * More formally, adds the specified element {@code e} to this set if
     * the set contains no element {@code e2} such that
     * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns {@code false}.
     *
     * @param e element to be added to this set
     * @return {@code true} if this set did not already contain the specified
     *         element
     */
    public boolean add(E e) {
        return al.addIfAbsent(e);
    }

    /**
     * Returns {@code true} if this set contains all of the elements of the
     * specified collection.  If the specified collection is also a set, this
     * method returns {@code true} if it is a <i>subset</i> of this set.
     *
     * @param  c collection to be checked for containment in this set
     * @return {@code true} if this set contains all of the elements of the
     *         specified collection
     * @throws NullPointerException if the specified collection is null
     * @see #contains(Object)
     */
    public boolean containsAll(Collection<?> c) {
        return al.containsAll(c);
    }

    /**
     * Adds all of the elements in the specified collection to this set if
     * they're not already present.  If the specified collection is also a
     * set, the {@code addAll} operation effectively modifies this set so
     * that its value is the <i>union</i> of the two sets.  The behavior of
     * this operation is undefined if the specified collection is modified
     * while the operation is in progress.
     *
     * @param  c collection containing elements to be added to this set
     * @return {@code true} if this set changed as a result of the call
     * @throws NullPointerException if the specified collection is null
     * @see #add(Object)
     */
    public boolean addAll(Collection<? extends E> c) {
        if (c instanceof Set)
            return al.addAll(c);
        else
            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;
    }

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

    public Stream<E> stream() {
        return Streams.stream(spliterator());
    }
    public Stream<E> parallelStream() {
        return Streams.parallelStream(spliterator());
    }

    /**
     * Tests for equality, coping with nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null) ? o2 == null : o1.equals(o2);
    }
}
Revision:	1.50
Committed:	Mon Feb 25 17:59:40 2013 UTC (11 years, 3 months ago) by dl
Branch:	MAIN
Changes since 1.49:	+6 -2 lines
Log Message:	lambda syncs and improvements
#	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.stream.Stream;
14	import java.util.Spliterator;
15	import java.util.Spliterators;
16	import java.util.stream.Streams;
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	al = new CopyOnWriteArrayList<E>();
90	al.addAllAbsent(c);
91	}
92
93	/**
94	* Returns the number of elements in this set.
95	*
96	* @return the number of elements in this set
97	*/
98	public int size() {
99	return al.size();
100	}
101
102	/**
103	* Returns {@code true} if this set contains no elements.
104	*
105	* @return {@code true} if this set contains no elements
106	*/
107	public boolean isEmpty() {
108	return al.isEmpty();
109	}
110
111	/**
112	* Returns {@code true} if this set contains the specified element.
113	* More formally, returns {@code true} if and only if this set
114	* contains an element {@code e} such that
115	* <tt>(o==null ? e==null : o.equals(e))</tt>.
116	*
117	* @param o element whose presence in this set is to be tested
118	* @return {@code true} if this set contains the specified element
119	*/
120	public boolean contains(Object o) {
121	return al.contains(o);
122	}
123
124	/**
125	* Returns an array containing all of the elements in this set.
126	* If this set makes any guarantees as to what order its elements
127	* are returned by its iterator, this method must return the
128	* elements in the same order.
129	*
130	* <p>The returned array will be "safe" in that no references to it
131	* are maintained by this set. (In other words, this method must
132	* allocate a new array even if this set is backed by an array).
133	* The caller is thus free to modify the returned array.
134	*
135	* <p>This method acts as bridge between array-based and collection-based
136	* APIs.
137	*
138	* @return an array containing all the elements in this set
139	*/
140	public Object[] toArray() {
141	return al.toArray();
142	}
143
144	/**
145	* Returns an array containing all of the elements in this set; the
146	* runtime type of the returned array is that of the specified array.
147	* If the set fits in the specified array, it is returned therein.
148	* Otherwise, a new array is allocated with the runtime type of the
149	* specified array and the size of this set.
150	*
151	* <p>If this set fits in the specified array with room to spare
152	* (i.e., the array has more elements than this set), the element in
153	* the array immediately following the end of the set is set to
154	* {@code null}. (This is useful in determining the length of this
155	* set <i>only</i> if the caller knows that this set does not contain
156	* any null elements.)
157	*
158	* <p>If this set makes any guarantees as to what order its elements
159	* are returned by its iterator, this method must return the elements
160	* in the same order.
161	*
162	* <p>Like the {@link #toArray()} method, this method acts as bridge between
163	* array-based and collection-based APIs. Further, this method allows
164	* precise control over the runtime type of the output array, and may,
165	* under certain circumstances, be used to save allocation costs.
166	*
167	* <p>Suppose {@code x} is a set known to contain only strings.
168	* The following code can be used to dump the set into a newly allocated
169	* array of {@code String}:
170	*
171	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
172	*
173	* Note that {@code toArray(new Object[0])} is identical in function to
174	* {@code toArray()}.
175	*
176	* @param a the array into which the elements of this set are to be
177	* stored, if it is big enough; otherwise, a new array of the same
178	* runtime type is allocated for this purpose.
179	* @return an array containing all the elements in this set
180	* @throws ArrayStoreException if the runtime type of the specified array
181	* is not a supertype of the runtime type of every element in this
182	* set
183	* @throws NullPointerException if the specified array is null
184	*/
185	public <T> T[] toArray(T[] a) {
186	return al.toArray(a);
187	}
188
189	/**
190	* Removes all of the elements from this set.
191	* The set will be empty after this call returns.
192	*/
193	public void clear() {
194	al.clear();
195	}
196
197	/**
198	* Removes the specified element from this set if it is present.
199	* More formally, removes an element {@code e} such that
200	* <tt>(o==null ? e==null : o.equals(e))</tt>,
201	* if this set contains such an element. Returns {@code true} if
202	* this set contained the element (or equivalently, if this set
203	* changed as a result of the call). (This set will not contain the
204	* element once the call returns.)
205	*
206	* @param o object to be removed from this set, if present
207	* @return {@code true} if this set contained the specified element
208	*/
209	public boolean remove(Object o) {
210	return al.remove(o);
211	}
212
213	/**
214	* Adds the specified element to this set if it is not already present.
215	* More formally, adds the specified element {@code e} to this set if
216	* the set contains no element {@code e2} such that
217	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
218	* If this set already contains the element, the call leaves the set
219	* unchanged and returns {@code false}.
220	*
221	* @param e element to be added to this set
222	* @return {@code true} if this set did not already contain the specified
223	* element
224	*/
225	public boolean add(E e) {
226	return al.addIfAbsent(e);
227	}
228
229	/**
230	* Returns {@code true} if this set contains all of the elements of the
231	* specified collection. If the specified collection is also a set, this
232	* method returns {@code true} if it is a <i>subset</i> of this set.
233	*
234	* @param c collection to be checked for containment in this set
235	* @return {@code true} if this set contains all of the elements of the
236	* specified collection
237	* @throws NullPointerException if the specified collection is null
238	* @see #contains(Object)
239	*/
240	public boolean containsAll(Collection<?> c) {
241	return al.containsAll(c);
242	}
243
244	/**
245	* Adds all of the elements in the specified collection to this set if
246	* they're not already present. If the specified collection is also a
247	* set, the {@code addAll} operation effectively modifies this set so
248	* that its value is the <i>union</i> of the two sets. The behavior of
249	* this operation is undefined if the specified collection is modified
250	* while the operation is in progress.
251	*
252	* @param c collection containing elements to be added to this set
253	* @return {@code true} if this set changed as a result of the call
254	* @throws NullPointerException if the specified collection is null
255	* @see #add(Object)
256	*/
257	public boolean addAll(Collection<? extends E> c) {
258	if (c instanceof Set)
259	return al.addAll(c);
260	else
261	return al.addAllAbsent(c) > 0;
262	}
263
264	/**
265	* Removes from this set all of its elements that are contained in the
266	* specified collection. If the specified collection is also a set,
267	* this operation effectively modifies this set so that its value is the
268	* <i>asymmetric set difference</i> of the two sets.
269	*
270	* @param c collection containing elements to be removed from this set
271	* @return {@code true} if this set changed as a result of the call
272	* @throws ClassCastException if the class of an element of this set
273	* is incompatible with the specified collection (optional)
274	* @throws NullPointerException if this set contains a null element and the
275	* specified collection does not permit null elements (optional),
276	* or if the specified collection is null
277	* @see #remove(Object)
278	*/
279	public boolean removeAll(Collection<?> c) {
280	return al.removeAll(c);
281	}
282
283	/**
284	* Retains only the elements in this set that are contained in the
285	* specified collection. In other words, removes from this set all of
286	* its elements that are not contained in the specified collection. If
287	* the specified collection is also a set, this operation effectively
288	* modifies this set so that its value is the <i>intersection</i> of the
289	* two sets.
290	*
291	* @param c collection containing elements to be retained in this set
292	* @return {@code true} if this set changed as a result of the call
293	* @throws ClassCastException if the class of an element of this set
294	* is incompatible with the specified collection (optional)
295	* @throws NullPointerException if this set contains a null element and the
296	* specified collection does not permit null elements (optional),
297	* or if the specified collection is null
298	* @see #remove(Object)
299	*/
300	public boolean retainAll(Collection<?> c) {
301	return al.retainAll(c);
302	}
303
304	/**
305	* Returns an iterator over the elements contained in this set
306	* in the order in which these elements were added.
307	*
308	* <p>The returned iterator provides a snapshot of the state of the set
309	* when the iterator was constructed. No synchronization is needed while
310	* traversing the iterator. The iterator does <em>NOT</em> support the
311	* {@code remove} method.
312	*
313	* @return an iterator over the elements in this set
314	*/
315	public Iterator<E> iterator() {
316	return al.iterator();
317	}
318
319	/**
320	* Compares the specified object with this set for equality.
321	* Returns {@code true} if the specified object is the same object
322	* as this object, or if it is also a {@link Set} and the elements
323	* returned by an {@linkplain Set#iterator() iterator} over the
324	* specified set are the same as the elements returned by an
325	* iterator over this set. More formally, the two iterators are
326	* considered to return the same elements if they return the same
327	* number of elements and for every element {@code e1} returned by
328	* the iterator over the specified set, there is an element
329	* {@code e2} returned by the iterator over this set such that
330	* {@code (e1==null ? e2==null : e1.equals(e2))}.
331	*
332	* @param o object to be compared for equality with this set
333	* @return {@code true} if the specified object is equal to this set
334	*/
335	public boolean equals(Object o) {
336	if (o == this)
337	return true;
338	if (!(o instanceof Set))
339	return false;
340	Set<?> set = (Set<?>)(o);
341	Iterator<?> it = set.iterator();
342
343	// Uses O(n^2) algorithm that is only appropriate
344	// for small sets, which CopyOnWriteArraySets should be.
345
346	// Use a single snapshot of underlying array
347	Object[] elements = al.getArray();
348	int len = elements.length;
349	// Mark matched elements to avoid re-checking
350	boolean[] matched = new boolean[len];
351	int k = 0;
352	outer: while (it.hasNext()) {
353	if (++k > len)
354	return false;
355	Object x = it.next();
356	for (int i = 0; i < len; ++i) {
357	if (!matched[i] && eq(x, elements[i])) {
358	matched[i] = true;
359	continue outer;
360	}
361	}
362	return false;
363	}
364	return k == len;
365	}
366
367	Spliterator<E> spliterator() {
368	return Spliterators.spliterator
369	(al.getArray(), Spliterator.IMMUTABLE \|
370	Spliterator.DISTINCT \| Spliterator.ORDERED);
371	}
372
373	public Stream<E> stream() {
374	return Streams.stream(spliterator());
375	}
376	public Stream<E> parallelStream() {
377	return Streams.parallelStream(spliterator());
378	}
379
380	/**
381	* Tests for equality, coping with nulls.
382	*/
383	private static boolean eq(Object o1, Object o2) {
384	return (o1 == null) ? o2 == null : o1.equals(o2);
385	}
386	}