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;

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

    private final CopyOnWriteArrayList<E> al;

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

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

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

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

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

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

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

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

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

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

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

    /**
     * Adds all of the elements in the specified collection to this set if
     * they're not already present.  If the specified collection is also a
     * set, the {@code addAll} operation effectively modifies this set so
     * that its value is the <i>union</i> of the two sets.  The behavior of
     * this operation is undefined if the specified collection is modified
     * while the operation is in progress.
     *
     * @param  c collection containing elements to be added to this set
     * @return {@code true} if this set changed as a result of the call
     * @throws NullPointerException if the specified collection is null
     * @see #add(Object)
     */
    public boolean addAll(Collection<? extends E> c) {
        return al.addAllAbsent(c) > 0;
    }

    /**
     * Removes from this set all of its elements that are contained in the
     * specified collection.  If the specified collection is also a set,
     * this operation effectively modifies this set so that its value is the
     * <i>asymmetric set difference</i> of the two sets.
     *
     * @param  c collection containing elements to be removed from this set
     * @return {@code true} if this set changed as a result of the call
     * @throws ClassCastException if the class of an element of this set
     *         is incompatible with the specified collection (optional)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements (optional),
     *         or if the specified collection is null
     * @see #remove(Object)
     */
    public boolean removeAll(Collection<?> c) {
        return al.removeAll(c);
    }

    /**
     * Retains only the elements in this set that are contained in the
     * specified collection.  In other words, removes from this set all of
     * its elements that are not contained in the specified collection.  If
     * the specified collection is also a set, this operation effectively
     * modifies this set so that its value is the <i>intersection</i> of the
     * two sets.
     *
     * @param  c collection containing elements to be retained in this set
     * @return {@code true} if this set changed as a result of the call
     * @throws ClassCastException if the class of an element of this set
     *         is incompatible with the specified collection (optional)
     * @throws NullPointerException if this set contains a null element and the
     *         specified collection does not permit null elements (optional),
     *         or if the specified collection is null
     * @see #remove(Object)
     */
    public boolean retainAll(Collection<?> c) {
        return al.retainAll(c);
    }

    /**
     * Returns an iterator over the elements contained in this set
     * in the order in which these elements were added.
     *
     * <p>The returned iterator provides a snapshot of the state of the set
     * when the iterator was constructed. No synchronization is needed while
     * traversing the iterator. The iterator does <em>NOT</em> support the
     * {@code remove} method.
     *
     * @return an iterator over the elements in this set
     */
    public Iterator<E> iterator() {
        return al.iterator();
    }

    /**
     * Compares the specified object with this set for equality.
     * Returns {@code true} if the specified object is the same object
     * as this object, or if it is also a {@link Set} and the elements
     * returned by an {@linkplain Set#iterator() iterator} over the
     * specified set are the same as the elements returned by an
     * iterator over this set.  More formally, the two iterators are
     * considered to return the same elements if they return the same
     * number of elements and for every element {@code e1} returned by
     * the iterator over the specified set, there is an element
     * {@code e2} returned by the iterator over this set such that
     * {@code (e1==null ? e2==null : e1.equals(e2))}.
     *
     * @param o object to be compared for equality with this set
     * @return {@code true} if the specified object is equal to this set
     */
    public boolean equals(Object o) {
        if (o == this)
            return true;
        if (!(o instanceof Set))
            return false;
        Set<?> set = (Set<?>)(o);
        Iterator<?> it = set.iterator();

        // Uses O(n^2) algorithm that is only appropriate
        // for small sets, which CopyOnWriteArraySets should be.

        //  Use a single snapshot of underlying array
        Object[] elements = al.getArray();
        int len = elements.length;
        // Mark matched elements to avoid re-checking
        boolean[] matched = new boolean[len];
        int k = 0;
        outer: while (it.hasNext()) {
            if (++k > len)
                return false;
            Object x = it.next();
            for (int i = 0; i < len; ++i) {
                if (!matched[i] && eq(x, elements[i])) {
                    matched[i] = true;
                    continue outer;
                }
            }
            return false;
        }
        return k == len;
    }

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

    /**
     * Tests for equality, coping with nulls.
     */
    private static boolean eq(Object o1, Object o2) {
        return (o1 == null) ? o2 == null : o1.equals(o2);
    }
}
Revision:	1.53
Committed:	Thu May 2 05:56:15 2013 UTC (11 years, 1 month ago) by jsr166
Branch:	MAIN
Changes since 1.52:	+0 -1 lines
Log Message:	port to latest lambda
#	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
17	/**
18	* A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
19	* for all of its operations. Thus, it shares the same basic properties:
20	* <ul>
21	* <li>It is best suited for applications in which set sizes generally
22	* stay small, read-only operations
23	* vastly outnumber mutative operations, and you need
24	* to prevent interference among threads during traversal.
25	* <li>It is thread-safe.
26	* <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
27	* are expensive since they usually entail copying the entire underlying
28	* array.
29	* <li>Iterators do not support the mutative {@code remove} operation.
30	* <li>Traversal via iterators is fast and cannot encounter
31	* interference from other threads. Iterators rely on
32	* unchanging snapshots of the array at the time the iterators were
33	* constructed.
34	* </ul>
35	*
36	* <p><b>Sample Usage.</b> The following code sketch uses a
37	* copy-on-write set to maintain a set of Handler objects that
38	* perform some action upon state updates.
39	*
40	* <pre> {@code
41	* class Handler { void handle(); ... }
42	*
43	* class X {
44	* private final CopyOnWriteArraySet<Handler> handlers
45	* = new CopyOnWriteArraySet<Handler>();
46	* public void addHandler(Handler h) { handlers.add(h); }
47	*
48	* private long internalState;
49	* private synchronized void changeState() { internalState = ...; }
50	*
51	* public void update() {
52	* changeState();
53	* for (Handler handler : handlers)
54	* handler.handle();
55	* }
56	* }}</pre>
57	*
58	* <p>This class is a member of the
59	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
60	* Java Collections Framework</a>.
61	*
62	* @see CopyOnWriteArrayList
63	* @since 1.5
64	* @author Doug Lea
65	* @param <E> the type of elements held in this collection
66	*/
67	public class CopyOnWriteArraySet<E> extends AbstractSet<E>
68	implements java.io.Serializable {
69	private static final long serialVersionUID = 5457747651344034263L;
70
71	private final CopyOnWriteArrayList<E> al;
72
73	/**
74	* Creates an empty set.
75	*/
76	public CopyOnWriteArraySet() {
77	al = new CopyOnWriteArrayList<E>();
78	}
79
80	/**
81	* Creates a set containing all of the elements of the specified
82	* collection.
83	*
84	* @param c the collection of elements to initially contain
85	* @throws NullPointerException if the specified collection is null
86	*/
87	public CopyOnWriteArraySet(Collection<? extends E> c) {
88	al = new CopyOnWriteArrayList<E>();
89	al.addAllAbsent(c);
90	}
91
92	/**
93	* Returns the number of elements in this set.
94	*
95	* @return the number of elements in this set
96	*/
97	public int size() {
98	return al.size();
99	}
100
101	/**
102	* Returns {@code true} if this set contains no elements.
103	*
104	* @return {@code true} if this set contains no elements
105	*/
106	public boolean isEmpty() {
107	return al.isEmpty();
108	}
109
110	/**
111	* Returns {@code true} if this set contains the specified element.
112	* More formally, returns {@code true} if and only if this set
113	* contains an element {@code e} such that
114	* <tt>(o==null ? e==null : o.equals(e))</tt>.
115	*
116	* @param o element whose presence in this set is to be tested
117	* @return {@code true} if this set contains the specified element
118	*/
119	public boolean contains(Object o) {
120	return al.contains(o);
121	}
122
123	/**
124	* Returns an array containing all of the elements in this set.
125	* If this set makes any guarantees as to what order its elements
126	* are returned by its iterator, this method must return the
127	* elements in the same order.
128	*
129	* <p>The returned array will be "safe" in that no references to it
130	* are maintained by this set. (In other words, this method must
131	* allocate a new array even if this set is backed by an array).
132	* The caller is thus free to modify the returned array.
133	*
134	* <p>This method acts as bridge between array-based and collection-based
135	* APIs.
136	*
137	* @return an array containing all the elements in this set
138	*/
139	public Object[] toArray() {
140	return al.toArray();
141	}
142
143	/**
144	* Returns an array containing all of the elements in this set; the
145	* runtime type of the returned array is that of the specified array.
146	* If the set fits in the specified array, it is returned therein.
147	* Otherwise, a new array is allocated with the runtime type of the
148	* specified array and the size of this set.
149	*
150	* <p>If this set fits in the specified array with room to spare
151	* (i.e., the array has more elements than this set), the element in
152	* the array immediately following the end of the set is set to
153	* {@code null}. (This is useful in determining the length of this
154	* set <i>only</i> if the caller knows that this set does not contain
155	* any null elements.)
156	*
157	* <p>If this set makes any guarantees as to what order its elements
158	* are returned by its iterator, this method must return the elements
159	* in the same order.
160	*
161	* <p>Like the {@link #toArray()} method, this method acts as bridge between
162	* array-based and collection-based APIs. Further, this method allows
163	* precise control over the runtime type of the output array, and may,
164	* under certain circumstances, be used to save allocation costs.
165	*
166	* <p>Suppose {@code x} is a set known to contain only strings.
167	* The following code can be used to dump the set into a newly allocated
168	* array of {@code String}:
169	*
170	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
171	*
172	* Note that {@code toArray(new Object[0])} is identical in function to
173	* {@code toArray()}.
174	*
175	* @param a the array into which the elements of this set are to be
176	* stored, if it is big enough; otherwise, a new array of the same
177	* runtime type is allocated for this purpose.
178	* @return an array containing all the elements in this set
179	* @throws ArrayStoreException if the runtime type of the specified array
180	* is not a supertype of the runtime type of every element in this
181	* set
182	* @throws NullPointerException if the specified array is null
183	*/
184	public <T> T[] toArray(T[] a) {
185	return al.toArray(a);
186	}
187
188	/**
189	* Removes all of the elements from this set.
190	* The set will be empty after this call returns.
191	*/
192	public void clear() {
193	al.clear();
194	}
195
196	/**
197	* Removes the specified element from this set if it is present.
198	* More formally, removes an element {@code e} such that
199	* <tt>(o==null ? e==null : o.equals(e))</tt>,
200	* if this set contains such an element. Returns {@code true} if
201	* this set contained the element (or equivalently, if this set
202	* changed as a result of the call). (This set will not contain the
203	* element once the call returns.)
204	*
205	* @param o object to be removed from this set, if present
206	* @return {@code true} if this set contained the specified element
207	*/
208	public boolean remove(Object o) {
209	return al.remove(o);
210	}
211
212	/**
213	* Adds the specified element to this set if it is not already present.
214	* More formally, adds the specified element {@code e} to this set if
215	* the set contains no element {@code e2} such that
216	* <tt>(e==null ? e2==null : e.equals(e2))</tt>.
217	* If this set already contains the element, the call leaves the set
218	* unchanged and returns {@code false}.
219	*
220	* @param e element to be added to this set
221	* @return {@code true} if this set did not already contain the specified
222	* element
223	*/
224	public boolean add(E e) {
225	return al.addIfAbsent(e);
226	}
227
228	/**
229	* Returns {@code true} if this set contains all of the elements of the
230	* specified collection. If the specified collection is also a set, this
231	* method returns {@code true} if it is a <i>subset</i> of this set.
232	*
233	* @param c collection to be checked for containment in this set
234	* @return {@code true} if this set contains all of the elements of the
235	* specified collection
236	* @throws NullPointerException if the specified collection is null
237	* @see #contains(Object)
238	*/
239	public boolean containsAll(Collection<?> c) {
240	return al.containsAll(c);
241	}
242
243	/**
244	* Adds all of the elements in the specified collection to this set if
245	* they're not already present. If the specified collection is also a
246	* set, the {@code addAll} operation effectively modifies this set so
247	* that its value is the <i>union</i> of the two sets. The behavior of
248	* this operation is undefined if the specified collection is modified
249	* while the operation is in progress.
250	*
251	* @param c collection containing elements to be added to this set
252	* @return {@code true} if this set changed as a result of the call
253	* @throws NullPointerException if the specified collection is null
254	* @see #add(Object)
255	*/
256	public boolean addAll(Collection<? extends E> c) {
257	return al.addAllAbsent(c) > 0;
258	}
259
260	/**
261	* Removes from this set all of its elements that are contained in the
262	* specified collection. If the specified collection is also a set,
263	* this operation effectively modifies this set so that its value is the
264	* <i>asymmetric set difference</i> of the two sets.
265	*
266	* @param c collection containing elements to be removed from this set
267	* @return {@code true} if this set changed as a result of the call
268	* @throws ClassCastException if the class of an element of this set
269	* is incompatible with the specified collection (optional)
270	* @throws NullPointerException if this set contains a null element and the
271	* specified collection does not permit null elements (optional),
272	* or if the specified collection is null
273	* @see #remove(Object)
274	*/
275	public boolean removeAll(Collection<?> c) {
276	return al.removeAll(c);
277	}
278
279	/**
280	* Retains only the elements in this set that are contained in the
281	* specified collection. In other words, removes from this set all of
282	* its elements that are not contained in the specified collection. If
283	* the specified collection is also a set, this operation effectively
284	* modifies this set so that its value is the <i>intersection</i> of the
285	* two sets.
286	*
287	* @param c collection containing elements to be retained in this set
288	* @return {@code true} if this set changed as a result of the call
289	* @throws ClassCastException if the class of an element of this set
290	* is incompatible with the specified collection (optional)
291	* @throws NullPointerException if this set contains a null element and the
292	* specified collection does not permit null elements (optional),
293	* or if the specified collection is null
294	* @see #remove(Object)
295	*/
296	public boolean retainAll(Collection<?> c) {
297	return al.retainAll(c);
298	}
299
300	/**
301	* Returns an iterator over the elements contained in this set
302	* in the order in which these elements were added.
303	*
304	* <p>The returned iterator provides a snapshot of the state of the set
305	* when the iterator was constructed. No synchronization is needed while
306	* traversing the iterator. The iterator does <em>NOT</em> support the
307	* {@code remove} method.
308	*
309	* @return an iterator over the elements in this set
310	*/
311	public Iterator<E> iterator() {
312	return al.iterator();
313	}
314
315	/**
316	* Compares the specified object with this set for equality.
317	* Returns {@code true} if the specified object is the same object
318	* as this object, or if it is also a {@link Set} and the elements
319	* returned by an {@linkplain Set#iterator() iterator} over the
320	* specified set are the same as the elements returned by an
321	* iterator over this set. More formally, the two iterators are
322	* considered to return the same elements if they return the same
323	* number of elements and for every element {@code e1} returned by
324	* the iterator over the specified set, there is an element
325	* {@code e2} returned by the iterator over this set such that
326	* {@code (e1==null ? e2==null : e1.equals(e2))}.
327	*
328	* @param o object to be compared for equality with this set
329	* @return {@code true} if the specified object is equal to this set
330	*/
331	public boolean equals(Object o) {
332	if (o == this)
333	return true;
334	if (!(o instanceof Set))
335	return false;
336	Set<?> set = (Set<?>)(o);
337	Iterator<?> it = set.iterator();
338
339	// Uses O(n^2) algorithm that is only appropriate
340	// for small sets, which CopyOnWriteArraySets should be.
341
342	// Use a single snapshot of underlying array
343	Object[] elements = al.getArray();
344	int len = elements.length;
345	// Mark matched elements to avoid re-checking
346	boolean[] matched = new boolean[len];
347	int k = 0;
348	outer: while (it.hasNext()) {
349	if (++k > len)
350	return false;
351	Object x = it.next();
352	for (int i = 0; i < len; ++i) {
353	if (!matched[i] && eq(x, elements[i])) {
354	matched[i] = true;
355	continue outer;
356	}
357	}
358	return false;
359	}
360	return k == len;
361	}
362
363	public Spliterator<E> spliterator() {
364	return Spliterators.spliterator
365	(al.getArray(), Spliterator.IMMUTABLE \|
366	Spliterator.DISTINCT \| Spliterator.ORDERED);
367	}
368
369	/**
370	* Tests for equality, coping with nulls.
371	*/
372	private static boolean eq(Object o1, Object o2) {
373	return (o1 == null) ? o2 == null : o1.equals(o2);
374	}
375	}