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root/jsr166/jsr166/src/main/java/util/Collection.java
Revision: 1.12
Committed: Sat May 7 12:22:03 2011 UTC (13 years ago) by dl
Branch: MAIN
CVS Tags: HEAD
Changes since 1.11: +0 -0 lines
State: FILE REMOVED
Log Message: 
Stop shadowing OpenJDK classes not originated by jsr166

File Contents

# User Rev Content
1 dl 1.1 /*
2 jsr166 1.11 * Copyright (c) 1997, 2006, Oracle and/or its affiliates. All rights reserved.
3 jsr166 1.7 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 dl 1.1 *
5 jsr166 1.7 * This code is free software; you can redistribute it and/or modify it
6     * under the terms of the GNU General Public License version 2 only, as
7     * published by the Free Software Foundation. Sun designates this
8     * particular file as subject to the "Classpath" exception as provided
9     * by Sun in the LICENSE file that accompanied this code.
10     *
11     * This code is distributed in the hope that it will be useful, but WITHOUT
12     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13     * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14     * version 2 for more details (a copy is included in the LICENSE file that
15     * accompanied this code).
16     *
17     * You should have received a copy of the GNU General Public License version
18     * 2 along with this work; if not, write to the Free Software Foundation,
19     * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20     *
21 jsr166 1.11 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22     * or visit www.oracle.com if you need additional information or have any
23     * questions.
24 dl 1.1 */
25    
26     package java.util;
27    
28     /**
29     * The root interface in the <i>collection hierarchy</i>. A collection
30     * represents a group of objects, known as its <i>elements</i>. Some
31     * collections allow duplicate elements and others do not. Some are ordered
32     * and others unordered. The JDK does not provide any <i>direct</i>
33     * implementations of this interface: it provides implementations of more
34     * specific subinterfaces like <tt>Set</tt> and <tt>List</tt>. This interface
35     * is typically used to pass collections around and manipulate them where
36     * maximum generality is desired.
37     *
38     * <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain
39     * duplicate elements) should implement this interface directly.
40     *
41     * <p>All general-purpose <tt>Collection</tt> implementation classes (which
42     * typically implement <tt>Collection</tt> indirectly through one of its
43     * subinterfaces) should provide two "standard" constructors: a void (no
44     * arguments) constructor, which creates an empty collection, and a
45     * constructor with a single argument of type <tt>Collection</tt>, which
46     * creates a new collection with the same elements as its argument. In
47     * effect, the latter constructor allows the user to copy any collection,
48     * producing an equivalent collection of the desired implementation type.
49     * There is no way to enforce this convention (as interfaces cannot contain
50     * constructors) but all of the general-purpose <tt>Collection</tt>
51     * implementations in the Java platform libraries comply.
52     *
53     * <p>The "destructive" methods contained in this interface, that is, the
54     * methods that modify the collection on which they operate, are specified to
55     * throw <tt>UnsupportedOperationException</tt> if this collection does not
56     * support the operation. If this is the case, these methods may, but are not
57     * required to, throw an <tt>UnsupportedOperationException</tt> if the
58     * invocation would have no effect on the collection. For example, invoking
59     * the {@link #addAll(Collection)} method on an unmodifiable collection may,
60     * but is not required to, throw the exception if the collection to be added
61     * is empty.
62     *
63     * <p>Some collection implementations have restrictions on the elements that
64     * they may contain. For example, some implementations prohibit null elements,
65     * and some have restrictions on the types of their elements. Attempting to
66     * add an ineligible element throws an unchecked exception, typically
67     * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>. Attempting
68     * to query the presence of an ineligible element may throw an exception,
69     * or it may simply return false; some implementations will exhibit the former
70     * behavior and some will exhibit the latter. More generally, attempting an
71     * operation on an ineligible element whose completion would not result in
72     * the insertion of an ineligible element into the collection may throw an
73     * exception or it may succeed, at the option of the implementation.
74     * Such exceptions are marked as "optional" in the specification for this
75     * interface.
76     *
77     * <p>It is up to each collection to determine its own synchronization
78     * policy. In the absence of a stronger guarantee by the
79 dl 1.3 * implementation, undefined behavior may result from the invocation
80 dl 1.1 * of any method on a collection that is being mutated by another
81     * thread; this includes direct invocations, passing the collection to
82     * a method that might perform invocations, and using an existing
83     * iterator to examine the collection.
84     *
85     * <p>Many methods in Collections Framework interfaces are defined in
86     * terms of the {@link Object#equals(Object) equals} method. For example,
87     * the specification for the {@link #contains(Object) contains(Object o)}
88     * method says: "returns <tt>true</tt> if and only if this collection
89     * contains at least one element <tt>e</tt> such that
90     * <tt>(o==null ? e==null : o.equals(e))</tt>." This specification should
91     * <i>not</i> be construed to imply that invoking <tt>Collection.contains</tt>
92     * with a non-null argument <tt>o</tt> will cause <tt>o.equals(e)</tt> to be
93     * invoked for any element <tt>e</tt>. Implementations are free to implement
94     * optimizations whereby the <tt>equals</tt> invocation is avoided, for
95     * example, by first comparing the hash codes of the two elements. (The
96     * {@link Object#hashCode()} specification guarantees that two objects with
97     * unequal hash codes cannot be equal.) More generally, implementations of
98     * the various Collections Framework interfaces are free to take advantage of
99     * the specified behavior of underlying {@link Object} methods wherever the
100     * implementor deems it appropriate.
101     *
102     * <p>This interface is a member of the
103 jsr166 1.5 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
104 dl 1.1 * Java Collections Framework</a>.
105     *
106     * @author Josh Bloch
107     * @author Neal Gafter
108 jsr166 1.8 * @see Set
109     * @see List
110     * @see Map
111     * @see SortedSet
112     * @see SortedMap
113     * @see HashSet
114     * @see TreeSet
115     * @see ArrayList
116     * @see LinkedList
117     * @see Vector
118 dl 1.1 * @see Collections
119 jsr166 1.8 * @see Arrays
120     * @see AbstractCollection
121 dl 1.1 * @since 1.2
122     */
123    
124     public interface Collection<E> extends Iterable<E> {
125     // Query Operations
126    
127     /**
128     * Returns the number of elements in this collection. If this collection
129     * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
130     * <tt>Integer.MAX_VALUE</tt>.
131     *
132     * @return the number of elements in this collection
133     */
134     int size();
135    
136     /**
137     * Returns <tt>true</tt> if this collection contains no elements.
138     *
139     * @return <tt>true</tt> if this collection contains no elements
140     */
141     boolean isEmpty();
142    
143     /**
144     * Returns <tt>true</tt> if this collection contains the specified element.
145     * More formally, returns <tt>true</tt> if and only if this collection
146     * contains at least one element <tt>e</tt> such that
147     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
148     *
149     * @param o element whose presence in this collection is to be tested
150     * @return <tt>true</tt> if this collection contains the specified
151     * element
152     * @throws ClassCastException if the type of the specified element
153     * is incompatible with this collection (optional)
154     * @throws NullPointerException if the specified element is null and this
155     * collection does not permit null elements (optional)
156     */
157     boolean contains(Object o);
158    
159     /**
160     * Returns an iterator over the elements in this collection. There are no
161     * guarantees concerning the order in which the elements are returned
162     * (unless this collection is an instance of some class that provides a
163     * guarantee).
164     *
165     * @return an <tt>Iterator</tt> over the elements in this collection
166     */
167     Iterator<E> iterator();
168    
169     /**
170     * Returns an array containing all of the elements in this collection.
171     * If this collection makes any guarantees as to what order its elements
172     * are returned by its iterator, this method must return the elements in
173     * the same order.
174     *
175     * <p>The returned array will be "safe" in that no references to it are
176     * maintained by this collection. (In other words, this method must
177     * allocate a new array even if this collection is backed by an array).
178     * The caller is thus free to modify the returned array.
179     *
180     * <p>This method acts as bridge between array-based and collection-based
181     * APIs.
182     *
183     * @return an array containing all of the elements in this collection
184     */
185     Object[] toArray();
186    
187     /**
188     * Returns an array containing all of the elements in this collection;
189     * the runtime type of the returned array is that of the specified array.
190     * If the collection fits in the specified array, it is returned therein.
191     * Otherwise, a new array is allocated with the runtime type of the
192     * specified array and the size of this collection.
193     *
194     * <p>If this collection fits in the specified array with room to spare
195     * (i.e., the array has more elements than this collection), the element
196     * in the array immediately following the end of the collection is set to
197     * <tt>null</tt>. (This is useful in determining the length of this
198     * collection <i>only</i> if the caller knows that this collection does
199     * not contain any <tt>null</tt> elements.)
200     *
201     * <p>If this collection makes any guarantees as to what order its elements
202     * are returned by its iterator, this method must return the elements in
203     * the same order.
204     *
205     * <p>Like the {@link #toArray()} method, this method acts as bridge between
206     * array-based and collection-based APIs. Further, this method allows
207     * precise control over the runtime type of the output array, and may,
208     * under certain circumstances, be used to save allocation costs.
209     *
210     * <p>Suppose <tt>x</tt> is a collection known to contain only strings.
211     * The following code can be used to dump the collection into a newly
212     * allocated array of <tt>String</tt>:
213     *
214     * <pre>
215     * String[] y = x.toArray(new String[0]);</pre>
216     *
217     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
218     * <tt>toArray()</tt>.
219     *
220     * @param a the array into which the elements of this collection are to be
221     * stored, if it is big enough; otherwise, a new array of the same
222     * runtime type is allocated for this purpose.
223     * @return an array containing all of the elements in this collection
224     * @throws ArrayStoreException if the runtime type of the specified array
225     * is not a supertype of the runtime type of every element in
226     * this collection
227     * @throws NullPointerException if the specified array is null
228     */
229     <T> T[] toArray(T[] a);
230    
231     // Modification Operations
232    
233     /**
234     * Ensures that this collection contains the specified element (optional
235     * operation). Returns <tt>true</tt> if this collection changed as a
236     * result of the call. (Returns <tt>false</tt> if this collection does
237     * not permit duplicates and already contains the specified element.)<p>
238     *
239     * Collections that support this operation may place limitations on what
240     * elements may be added to this collection. In particular, some
241     * collections will refuse to add <tt>null</tt> elements, and others will
242     * impose restrictions on the type of elements that may be added.
243     * Collection classes should clearly specify in their documentation any
244     * restrictions on what elements may be added.<p>
245     *
246     * If a collection refuses to add a particular element for any reason
247     * other than that it already contains the element, it <i>must</i> throw
248     * an exception (rather than returning <tt>false</tt>). This preserves
249     * the invariant that a collection always contains the specified element
250     * after this call returns.
251     *
252     * @param e element whose presence in this collection is to be ensured
253     * @return <tt>true</tt> if this collection changed as a result of the
254     * call
255     * @throws UnsupportedOperationException if the <tt>add</tt> operation
256     * is not supported by this collection
257     * @throws ClassCastException if the class of the specified element
258     * prevents it from being added to this collection
259     * @throws NullPointerException if the specified element is null and this
260     * collection does not permit null elements
261     * @throws IllegalArgumentException if some property of the element
262     * prevents it from being added to this collection
263     * @throws IllegalStateException if the element cannot be added at this
264     * time due to insertion restrictions
265     */
266     boolean add(E e);
267    
268     /**
269     * Removes a single instance of the specified element from this
270     * collection, if it is present (optional operation). More formally,
271     * removes an element <tt>e</tt> such that
272     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>, if
273     * this collection contains one or more such elements. Returns
274     * <tt>true</tt> if this collection contained the specified element (or
275     * equivalently, if this collection changed as a result of the call).
276     *
277     * @param o element to be removed from this collection, if present
278     * @return <tt>true</tt> if an element was removed as a result of this call
279     * @throws ClassCastException if the type of the specified element
280 jsr166 1.8 * is incompatible with this collection (optional)
281 dl 1.1 * @throws NullPointerException if the specified element is null and this
282     * collection does not permit null elements (optional)
283     * @throws UnsupportedOperationException if the <tt>remove</tt> operation
284     * is not supported by this collection
285     */
286     boolean remove(Object o);
287    
288    
289     // Bulk Operations
290    
291     /**
292     * Returns <tt>true</tt> if this collection contains all of the elements
293     * in the specified collection.
294     *
295     * @param c collection to be checked for containment in this collection
296     * @return <tt>true</tt> if this collection contains all of the elements
297 jsr166 1.8 * in the specified collection
298 dl 1.1 * @throws ClassCastException if the types of one or more elements
299     * in the specified collection are incompatible with this
300     * collection (optional)
301     * @throws NullPointerException if the specified collection contains one
302     * or more null elements and this collection does not permit null
303     * elements (optional), or if the specified collection is null
304     * @see #contains(Object)
305     */
306     boolean containsAll(Collection<?> c);
307    
308     /**
309     * Adds all of the elements in the specified collection to this collection
310     * (optional operation). The behavior of this operation is undefined if
311     * the specified collection is modified while the operation is in progress.
312     * (This implies that the behavior of this call is undefined if the
313     * specified collection is this collection, and this collection is
314     * nonempty.)
315     *
316     * @param c collection containing elements to be added to this collection
317     * @return <tt>true</tt> if this collection changed as a result of the call
318     * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
319     * is not supported by this collection
320     * @throws ClassCastException if the class of an element of the specified
321     * collection prevents it from being added to this collection
322     * @throws NullPointerException if the specified collection contains a
323     * null element and this collection does not permit null elements,
324     * or if the specified collection is null
325     * @throws IllegalArgumentException if some property of an element of the
326     * specified collection prevents it from being added to this
327     * collection
328     * @throws IllegalStateException if not all the elements can be added at
329     * this time due to insertion restrictions
330     * @see #add(Object)
331     */
332     boolean addAll(Collection<? extends E> c);
333    
334     /**
335     * Removes all of this collection's elements that are also contained in the
336     * specified collection (optional operation). After this call returns,
337     * this collection will contain no elements in common with the specified
338     * collection.
339     *
340     * @param c collection containing elements to be removed from this collection
341     * @return <tt>true</tt> if this collection changed as a result of the
342     * call
343     * @throws UnsupportedOperationException if the <tt>removeAll</tt> method
344     * is not supported by this collection
345     * @throws ClassCastException if the types of one or more elements
346     * in this collection are incompatible with the specified
347     * collection (optional)
348     * @throws NullPointerException if this collection contains one or more
349     * null elements and the specified collection does not support
350     * null elements (optional), or if the specified collection is null
351     * @see #remove(Object)
352     * @see #contains(Object)
353     */
354     boolean removeAll(Collection<?> c);
355    
356     /**
357     * Retains only the elements in this collection that are contained in the
358     * specified collection (optional operation). In other words, removes from
359     * this collection all of its elements that are not contained in the
360     * specified collection.
361     *
362     * @param c collection containing elements to be retained in this collection
363     * @return <tt>true</tt> if this collection changed as a result of the call
364     * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
365     * is not supported by this collection
366     * @throws ClassCastException if the types of one or more elements
367     * in this collection are incompatible with the specified
368     * collection (optional)
369     * @throws NullPointerException if this collection contains one or more
370     * null elements and the specified collection does not permit null
371     * elements (optional), or if the specified collection is null
372     * @see #remove(Object)
373     * @see #contains(Object)
374     */
375     boolean retainAll(Collection<?> c);
376    
377     /**
378     * Removes all of the elements from this collection (optional operation).
379     * The collection will be empty after this method returns.
380     *
381     * @throws UnsupportedOperationException if the <tt>clear</tt> operation
382     * is not supported by this collection
383     */
384     void clear();
385    
386    
387     // Comparison and hashing
388    
389     /**
390     * Compares the specified object with this collection for equality. <p>
391     *
392     * While the <tt>Collection</tt> interface adds no stipulations to the
393     * general contract for the <tt>Object.equals</tt>, programmers who
394     * implement the <tt>Collection</tt> interface "directly" (in other words,
395     * create a class that is a <tt>Collection</tt> but is not a <tt>Set</tt>
396     * or a <tt>List</tt>) must exercise care if they choose to override the
397     * <tt>Object.equals</tt>. It is not necessary to do so, and the simplest
398     * course of action is to rely on <tt>Object</tt>'s implementation, but
399     * the implementor may wish to implement a "value comparison" in place of
400     * the default "reference comparison." (The <tt>List</tt> and
401     * <tt>Set</tt> interfaces mandate such value comparisons.)<p>
402     *
403     * The general contract for the <tt>Object.equals</tt> method states that
404     * equals must be symmetric (in other words, <tt>a.equals(b)</tt> if and
405     * only if <tt>b.equals(a)</tt>). The contracts for <tt>List.equals</tt>
406     * and <tt>Set.equals</tt> state that lists are only equal to other lists,
407     * and sets to other sets. Thus, a custom <tt>equals</tt> method for a
408     * collection class that implements neither the <tt>List</tt> nor
409     * <tt>Set</tt> interface must return <tt>false</tt> when this collection
410     * is compared to any list or set. (By the same logic, it is not possible
411     * to write a class that correctly implements both the <tt>Set</tt> and
412     * <tt>List</tt> interfaces.)
413     *
414     * @param o object to be compared for equality with this collection
415     * @return <tt>true</tt> if the specified object is equal to this
416     * collection
417     *
418     * @see Object#equals(Object)
419     * @see Set#equals(Object)
420     * @see List#equals(Object)
421     */
422     boolean equals(Object o);
423    
424     /**
425     * Returns the hash code value for this collection. While the
426     * <tt>Collection</tt> interface adds no stipulations to the general
427     * contract for the <tt>Object.hashCode</tt> method, programmers should
428     * take note that any class that overrides the <tt>Object.equals</tt>
429     * method must also override the <tt>Object.hashCode</tt> method in order
430 jsr166 1.10 * to satisfy the general contract for the <tt>Object.hashCode</tt> method.
431 dl 1.1 * In particular, <tt>c1.equals(c2)</tt> implies that
432     * <tt>c1.hashCode()==c2.hashCode()</tt>.
433     *
434     * @return the hash code value for this collection
435     *
436     * @see Object#hashCode()
437     * @see Object#equals(Object)
438     */
439     int hashCode();
440     }