1 |
dl |
1.2 |
/* |
2 |
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* 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 |
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7 |
tim |
1.1 |
package java.util.concurrent; |
8 |
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import java.util.*; |
9 |
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10 |
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/** |
11 |
jsr166 |
1.26 |
* A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList} |
12 |
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* for all of its operations. Thus, it shares the same basic properties: |
13 |
tim |
1.1 |
* <ul> |
14 |
dholmes |
1.7 |
* <li>It is best suited for applications in which set sizes generally |
15 |
tim |
1.1 |
* stay small, read-only operations |
16 |
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* vastly outnumber mutative operations, and you need |
17 |
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* to prevent interference among threads during traversal. |
18 |
dl |
1.16 |
* <li>It is thread-safe. |
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jsr166 |
1.26 |
* <li>Mutative operations (<tt>add</tt>, <tt>set</tt>, <tt>remove</tt>, etc.) |
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* are expensive since they usually entail copying the entire underlying |
21 |
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* array. |
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* <li>Iterators do not support the mutative <tt>remove</tt> operation. |
23 |
dl |
1.18 |
* <li>Traversal via iterators is fast and cannot encounter |
24 |
tim |
1.1 |
* interference from other threads. Iterators rely on |
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* unchanging snapshots of the array at the time the iterators were |
26 |
jsr166 |
1.26 |
* constructed. |
27 |
tim |
1.1 |
* </ul> |
28 |
dl |
1.18 |
* |
29 |
jsr166 |
1.42 |
* <p><b>Sample Usage.</b> The following code sketch uses a |
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jsr166 |
1.21 |
* copy-on-write set to maintain a set of Handler objects that |
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* perform some action upon state updates. |
32 |
dl |
1.18 |
* |
33 |
jsr166 |
1.37 |
* <pre> {@code |
34 |
tim |
1.6 |
* class Handler { void handle(); ... } |
35 |
tim |
1.1 |
* |
36 |
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* class X { |
37 |
jsr166 |
1.37 |
* private final CopyOnWriteArraySet<Handler> handlers |
38 |
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* = new CopyOnWriteArraySet<Handler>(); |
39 |
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* public void addHandler(Handler h) { handlers.add(h); } |
40 |
tim |
1.1 |
* |
41 |
jsr166 |
1.37 |
* private long internalState; |
42 |
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* private synchronized void changeState() { internalState = ...; } |
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tim |
1.1 |
* |
44 |
jsr166 |
1.37 |
* public void update() { |
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* changeState(); |
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* for (Handler handler : handlers) |
47 |
jsr166 |
1.43 |
* handler.handle(); |
48 |
jsr166 |
1.37 |
* } |
49 |
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* }}</pre> |
50 |
dl |
1.14 |
* |
51 |
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* <p>This class is a member of the |
52 |
jsr166 |
1.34 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
53 |
dl |
1.14 |
* Java Collections Framework</a>. |
54 |
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* |
55 |
dl |
1.16 |
* @see CopyOnWriteArrayList |
56 |
dl |
1.4 |
* @since 1.5 |
57 |
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* @author Doug Lea |
58 |
dl |
1.11 |
* @param <E> the type of elements held in this collection |
59 |
dl |
1.4 |
*/ |
60 |
tim |
1.1 |
public class CopyOnWriteArraySet<E> extends AbstractSet<E> |
61 |
dl |
1.18 |
implements java.io.Serializable { |
62 |
dl |
1.8 |
private static final long serialVersionUID = 5457747651344034263L; |
63 |
tim |
1.1 |
|
64 |
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private final CopyOnWriteArrayList<E> al; |
65 |
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/** |
67 |
dl |
1.15 |
* Creates an empty set. |
68 |
tim |
1.1 |
*/ |
69 |
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public CopyOnWriteArraySet() { |
70 |
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al = new CopyOnWriteArrayList<E>(); |
71 |
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} |
72 |
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/** |
74 |
dl |
1.15 |
* Creates a set containing all of the elements of the specified |
75 |
jsr166 |
1.23 |
* collection. |
76 |
jsr166 |
1.25 |
* |
77 |
jsr166 |
1.23 |
* @param c the collection of elements to initially contain |
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* @throws NullPointerException if the specified collection is null |
79 |
tim |
1.1 |
*/ |
80 |
tim |
1.12 |
public CopyOnWriteArraySet(Collection<? extends E> c) { |
81 |
tim |
1.1 |
al = new CopyOnWriteArrayList<E>(); |
82 |
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al.addAllAbsent(c); |
83 |
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} |
84 |
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85 |
jsr166 |
1.26 |
/** |
86 |
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* Returns the number of elements in this set. |
87 |
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* |
88 |
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* @return the number of elements in this set |
89 |
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*/ |
90 |
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public int size() { |
91 |
jsr166 |
1.36 |
return al.size(); |
92 |
jsr166 |
1.26 |
} |
93 |
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/** |
95 |
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* Returns <tt>true</tt> if this set contains no elements. |
96 |
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* |
97 |
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* @return <tt>true</tt> if this set contains no elements |
98 |
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*/ |
99 |
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public boolean isEmpty() { |
100 |
jsr166 |
1.36 |
return al.isEmpty(); |
101 |
jsr166 |
1.26 |
} |
102 |
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103 |
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/** |
104 |
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* Returns <tt>true</tt> if this set contains the specified element. |
105 |
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* More formally, returns <tt>true</tt> if and only if this set |
106 |
jsr166 |
1.28 |
* contains an element <tt>e</tt> such that |
107 |
jsr166 |
1.26 |
* <tt>(o==null ? e==null : o.equals(e))</tt>. |
108 |
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* |
109 |
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* @param o element whose presence in this set is to be tested |
110 |
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* @return <tt>true</tt> if this set contains the specified element |
111 |
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*/ |
112 |
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public boolean contains(Object o) { |
113 |
jsr166 |
1.36 |
return al.contains(o); |
114 |
jsr166 |
1.26 |
} |
115 |
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116 |
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/** |
117 |
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* Returns an array containing all of the elements in this set. |
118 |
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* If this set makes any guarantees as to what order its elements |
119 |
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* are returned by its iterator, this method must return the |
120 |
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* elements in the same order. |
121 |
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* |
122 |
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* <p>The returned array will be "safe" in that no references to it |
123 |
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* are maintained by this set. (In other words, this method must |
124 |
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* allocate a new array even if this set is backed by an array). |
125 |
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* The caller is thus free to modify the returned array. |
126 |
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* |
127 |
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* <p>This method acts as bridge between array-based and collection-based |
128 |
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* APIs. |
129 |
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* |
130 |
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* @return an array containing all the elements in this set |
131 |
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*/ |
132 |
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public Object[] toArray() { |
133 |
jsr166 |
1.36 |
return al.toArray(); |
134 |
jsr166 |
1.26 |
} |
135 |
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136 |
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/** |
137 |
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* Returns an array containing all of the elements in this set; the |
138 |
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* runtime type of the returned array is that of the specified array. |
139 |
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* If the set fits in the specified array, it is returned therein. |
140 |
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* Otherwise, a new array is allocated with the runtime type of the |
141 |
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* specified array and the size of this set. |
142 |
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* |
143 |
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* <p>If this set fits in the specified array with room to spare |
144 |
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* (i.e., the array has more elements than this set), the element in |
145 |
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* the array immediately following the end of the set is set to |
146 |
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* <tt>null</tt>. (This is useful in determining the length of this |
147 |
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* set <i>only</i> if the caller knows that this set does not contain |
148 |
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* any null elements.) |
149 |
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* |
150 |
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* <p>If this set makes any guarantees as to what order its elements |
151 |
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* are returned by its iterator, this method must return the elements |
152 |
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* in the same order. |
153 |
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* |
154 |
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* <p>Like the {@link #toArray()} method, this method acts as bridge between |
155 |
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* array-based and collection-based APIs. Further, this method allows |
156 |
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* precise control over the runtime type of the output array, and may, |
157 |
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* under certain circumstances, be used to save allocation costs. |
158 |
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* |
159 |
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* <p>Suppose <tt>x</tt> is a set known to contain only strings. |
160 |
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* The following code can be used to dump the set into a newly allocated |
161 |
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* array of <tt>String</tt>: |
162 |
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* |
163 |
jsr166 |
1.40 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
164 |
jsr166 |
1.26 |
* |
165 |
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* Note that <tt>toArray(new Object[0])</tt> is identical in function to |
166 |
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* <tt>toArray()</tt>. |
167 |
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* |
168 |
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* @param a the array into which the elements of this set are to be |
169 |
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* stored, if it is big enough; otherwise, a new array of the same |
170 |
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* runtime type is allocated for this purpose. |
171 |
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* @return an array containing all the elements in this set |
172 |
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* @throws ArrayStoreException if the runtime type of the specified array |
173 |
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* is not a supertype of the runtime type of every element in this |
174 |
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* set |
175 |
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* @throws NullPointerException if the specified array is null |
176 |
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*/ |
177 |
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public <T> T[] toArray(T[] a) { |
178 |
jsr166 |
1.36 |
return al.toArray(a); |
179 |
jsr166 |
1.26 |
} |
180 |
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181 |
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/** |
182 |
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* Removes all of the elements from this set. |
183 |
jsr166 |
1.27 |
* The set will be empty after this call returns. |
184 |
jsr166 |
1.26 |
*/ |
185 |
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public void clear() { |
186 |
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al.clear(); |
187 |
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} |
188 |
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189 |
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/** |
190 |
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* Removes the specified element from this set if it is present. |
191 |
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* More formally, removes an element <tt>e</tt> such that |
192 |
jsr166 |
1.28 |
* <tt>(o==null ? e==null : o.equals(e))</tt>, |
193 |
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* if this set contains such an element. Returns <tt>true</tt> if |
194 |
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* this set contained the element (or equivalently, if this set |
195 |
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* changed as a result of the call). (This set will not contain the |
196 |
jsr166 |
1.26 |
* element once the call returns.) |
197 |
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* |
198 |
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* @param o object to be removed from this set, if present |
199 |
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* @return <tt>true</tt> if this set contained the specified element |
200 |
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*/ |
201 |
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public boolean remove(Object o) { |
202 |
jsr166 |
1.36 |
return al.remove(o); |
203 |
jsr166 |
1.26 |
} |
204 |
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205 |
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/** |
206 |
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* Adds the specified element to this set if it is not already present. |
207 |
jsr166 |
1.28 |
* More formally, adds the specified element <tt>e</tt> to this set if |
208 |
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* the set contains no element <tt>e2</tt> such that |
209 |
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* <tt>(e==null ? e2==null : e.equals(e2))</tt>. |
210 |
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* If this set already contains the element, the call leaves the set |
211 |
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* unchanged and returns <tt>false</tt>. |
212 |
jsr166 |
1.26 |
* |
213 |
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* @param e element to be added to this set |
214 |
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* @return <tt>true</tt> if this set did not already contain the specified |
215 |
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* element |
216 |
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*/ |
217 |
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public boolean add(E e) { |
218 |
jsr166 |
1.36 |
return al.addIfAbsent(e); |
219 |
jsr166 |
1.26 |
} |
220 |
tim |
1.1 |
|
221 |
jsr166 |
1.26 |
/** |
222 |
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* Returns <tt>true</tt> if this set contains all of the elements of the |
223 |
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* specified collection. If the specified collection is also a set, this |
224 |
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* method returns <tt>true</tt> if it is a <i>subset</i> of this set. |
225 |
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* |
226 |
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* @param c collection to be checked for containment in this set |
227 |
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* @return <tt>true</tt> if this set contains all of the elements of the |
228 |
jsr166 |
1.36 |
* specified collection |
229 |
jsr166 |
1.26 |
* @throws NullPointerException if the specified collection is null |
230 |
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* @see #contains(Object) |
231 |
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*/ |
232 |
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public boolean containsAll(Collection<?> c) { |
233 |
jsr166 |
1.36 |
return al.containsAll(c); |
234 |
jsr166 |
1.26 |
} |
235 |
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|
236 |
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/** |
237 |
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* Adds all of the elements in the specified collection to this set if |
238 |
|
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* they're not already present. If the specified collection is also a |
239 |
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* set, the <tt>addAll</tt> operation effectively modifies this set so |
240 |
|
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* that its value is the <i>union</i> of the two sets. The behavior of |
241 |
jsr166 |
1.28 |
* this operation is undefined if the specified collection is modified |
242 |
jsr166 |
1.26 |
* while the operation is in progress. |
243 |
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* |
244 |
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* @param c collection containing elements to be added to this set |
245 |
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* @return <tt>true</tt> if this set changed as a result of the call |
246 |
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* @throws NullPointerException if the specified collection is null |
247 |
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* @see #add(Object) |
248 |
|
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*/ |
249 |
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public boolean addAll(Collection<? extends E> c) { |
250 |
jsr166 |
1.36 |
return al.addAllAbsent(c) > 0; |
251 |
jsr166 |
1.26 |
} |
252 |
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|
253 |
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/** |
254 |
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* Removes from this set all of its elements that are contained in the |
255 |
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* specified collection. If the specified collection is also a set, |
256 |
|
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* this operation effectively modifies this set so that its value is the |
257 |
|
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* <i>asymmetric set difference</i> of the two sets. |
258 |
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* |
259 |
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* @param c collection containing elements to be removed from this set |
260 |
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* @return <tt>true</tt> if this set changed as a result of the call |
261 |
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* @throws ClassCastException if the class of an element of this set |
262 |
|
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* is incompatible with the specified collection (optional) |
263 |
|
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* @throws NullPointerException if this set contains a null element and the |
264 |
|
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* specified collection does not permit null elements (optional), |
265 |
|
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* or if the specified collection is null |
266 |
|
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* @see #remove(Object) |
267 |
|
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*/ |
268 |
|
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public boolean removeAll(Collection<?> c) { |
269 |
jsr166 |
1.36 |
return al.removeAll(c); |
270 |
jsr166 |
1.26 |
} |
271 |
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|
272 |
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/** |
273 |
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* Retains only the elements in this set that are contained in the |
274 |
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* specified collection. In other words, removes from this set all of |
275 |
|
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* its elements that are not contained in the specified collection. If |
276 |
|
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* the specified collection is also a set, this operation effectively |
277 |
|
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* modifies this set so that its value is the <i>intersection</i> of the |
278 |
|
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* two sets. |
279 |
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* |
280 |
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* @param c collection containing elements to be retained in this set |
281 |
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* @return <tt>true</tt> if this set changed as a result of the call |
282 |
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* @throws ClassCastException if the class of an element of this set |
283 |
|
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* is incompatible with the specified collection (optional) |
284 |
|
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* @throws NullPointerException if this set contains a null element and the |
285 |
|
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* specified collection does not permit null elements (optional), |
286 |
|
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* or if the specified collection is null |
287 |
|
|
* @see #remove(Object) |
288 |
|
|
*/ |
289 |
|
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public boolean retainAll(Collection<?> c) { |
290 |
jsr166 |
1.36 |
return al.retainAll(c); |
291 |
jsr166 |
1.26 |
} |
292 |
tim |
1.1 |
|
293 |
dl |
1.20 |
/** |
294 |
jsr166 |
1.24 |
* Returns an iterator over the elements contained in this set |
295 |
dl |
1.20 |
* in the order in which these elements were added. |
296 |
jsr166 |
1.26 |
* |
297 |
|
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* <p>The returned iterator provides a snapshot of the state of the set |
298 |
|
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* when the iterator was constructed. No synchronization is needed while |
299 |
|
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* traversing the iterator. The iterator does <em>NOT</em> support the |
300 |
|
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* <tt>remove</tt> method. |
301 |
|
|
* |
302 |
|
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* @return an iterator over the elements in this set |
303 |
dl |
1.20 |
*/ |
304 |
jsr166 |
1.26 |
public Iterator<E> iterator() { |
305 |
jsr166 |
1.36 |
return al.iterator(); |
306 |
jsr166 |
1.26 |
} |
307 |
dl |
1.20 |
|
308 |
dl |
1.30 |
/** |
309 |
|
|
* Compares the specified object with this set for equality. |
310 |
jsr166 |
1.33 |
* Returns {@code true} if the specified object is the same object |
311 |
|
|
* as this object, or if it is also a {@link Set} and the elements |
312 |
|
|
* returned by an {@linkplain List#iterator() iterator} over the |
313 |
|
|
* specified set are the same as the elements returned by an |
314 |
|
|
* iterator over this set. More formally, the two iterators are |
315 |
|
|
* considered to return the same elements if they return the same |
316 |
|
|
* number of elements and for every element {@code e1} returned by |
317 |
|
|
* the iterator over the specified set, there is an element |
318 |
|
|
* {@code e2} returned by the iterator over this set such that |
319 |
|
|
* {@code (e1==null ? e2==null : e1.equals(e2))}. |
320 |
dl |
1.30 |
* |
321 |
|
|
* @param o object to be compared for equality with this set |
322 |
jsr166 |
1.33 |
* @return {@code true} if the specified object is equal to this set |
323 |
dl |
1.30 |
*/ |
324 |
|
|
public boolean equals(Object o) { |
325 |
|
|
if (o == this) |
326 |
|
|
return true; |
327 |
|
|
if (!(o instanceof Set)) |
328 |
|
|
return false; |
329 |
|
|
Set<?> set = (Set<?>)(o); |
330 |
jsr166 |
1.36 |
Iterator<?> it = set.iterator(); |
331 |
dl |
1.30 |
|
332 |
|
|
// Uses O(n^2) algorithm that is only appropriate |
333 |
|
|
// for small sets, which CopyOnWriteArraySets should be. |
334 |
|
|
|
335 |
|
|
// Use a single snapshot of underlying array |
336 |
jsr166 |
1.36 |
Object[] elements = al.getArray(); |
337 |
|
|
int len = elements.length; |
338 |
dl |
1.30 |
// Mark matched elements to avoid re-checking |
339 |
|
|
boolean[] matched = new boolean[len]; |
340 |
|
|
int k = 0; |
341 |
jsr166 |
1.33 |
outer: while (it.hasNext()) { |
342 |
dl |
1.30 |
if (++k > len) |
343 |
|
|
return false; |
344 |
jsr166 |
1.33 |
Object x = it.next(); |
345 |
dl |
1.30 |
for (int i = 0; i < len; ++i) { |
346 |
|
|
if (!matched[i] && eq(x, elements[i])) { |
347 |
|
|
matched[i] = true; |
348 |
jsr166 |
1.36 |
continue outer; |
349 |
dl |
1.30 |
} |
350 |
|
|
} |
351 |
jsr166 |
1.36 |
return false; |
352 |
dl |
1.30 |
} |
353 |
|
|
return k == len; |
354 |
|
|
} |
355 |
jsr166 |
1.32 |
|
356 |
dl |
1.30 |
/** |
357 |
jsr166 |
1.41 |
* Tests for equality, coping with nulls. |
358 |
dl |
1.30 |
*/ |
359 |
|
|
private static boolean eq(Object o1, Object o2) { |
360 |
jsr166 |
1.39 |
return (o1 == null) ? o2 == null : o1.equals(o2); |
361 |
dl |
1.30 |
} |
362 |
tim |
1.1 |
} |