1 *java.util.AbstractCollection* *AbstractCollection* This class provides a skelet
3 public abstract class AbstractCollection
4 extends |java.lang.Object|
5 implements |java.util.Collection|
7 |java.util.AbstractCollection_Description|
8 |java.util.AbstractCollection_Fields|
9 |java.util.AbstractCollection_Constructors|
10 |java.util.AbstractCollection_Methods|
12 ================================================================================
14 *java.util.AbstractCollection_Constructors*
15 |java.util.AbstractCollection()|Sole constructor.
17 *java.util.AbstractCollection_Methods*
18 |java.util.AbstractCollection.add(E)|Ensures that this collection contains the
19 |java.util.AbstractCollection.addAll(Collection)|Adds all of the elements in th
20 |java.util.AbstractCollection.clear()|Removes all of the elements from this col
21 |java.util.AbstractCollection.contains(Object)|Returns true if this collection
22 |java.util.AbstractCollection.containsAll(Collection)|Returns true if this coll
23 |java.util.AbstractCollection.isEmpty()|Returns true if this collection contain
24 |java.util.AbstractCollection.iterator()|Returns an iterator over the elements
25 |java.util.AbstractCollection.remove(Object)|Removes a single instance of the s
26 |java.util.AbstractCollection.removeAll(Collection)|Removes from this collectio
27 |java.util.AbstractCollection.retainAll(Collection)|Retains only the elements i
28 |java.util.AbstractCollection.size()|Returns the number of elements in this col
29 |java.util.AbstractCollection.toArray()|Returns an array containing all of the
30 |java.util.AbstractCollection.toArray(T[])|Returns an array containing all of t
31 |java.util.AbstractCollection.toString()|Returns a string representation of thi
33 *java.util.AbstractCollection_Description*
35 This class provides a skeletal implementation of the Collection interface, to
36 minimize the effort required to implement this interface.
38 To implement an unmodifiable collection, the programmer needs only to extend
39 this class and provide implementations for the iterator and size methods. (The
40 iterator returned by the iterator method must implement hasNext and next.)
42 To implement a modifiable collection, the programmer must additionally override
43 this class's add method (which otherwise throws an
44 UnsupportedOperationException), and the iterator returned by the iterator
45 method must additionally implement its remove method.
47 The programmer should generally provide a void (no argument) and Collection
48 constructor, as per the recommendation in the Collection interface
51 The documentation for each non-abstract methods in this class describes its
52 implementation in detail. Each of these methods may be overridden if the
53 collection being implemented admits a more efficient implementation.
55 This class is a member of the <a href="/../guide/collections/index.html"> Java
56 Collections Framework.
59 *java.util.AbstractCollection()*
61 protected AbstractCollection()
63 Sole constructor. (For invocation by subclass constructors, typically
67 *java.util.AbstractCollection.add(E)*
69 public boolean add(java.lang.Object o)
71 Ensures that this collection contains the specified element (optional
72 operation). Returns true if the collection changed as a result of the call.
73 (Returns false if this collection does not permit duplicates and already
74 contains the specified element.) Collections that support this operation may
75 place limitations on what elements may be added to the collection. In
76 particular, some collections will refuse to add null elements, and others will
77 impose restrictions on the type of elements that may be added. Collection
78 classes should clearly specify in their documentation any restrictions on what
79 elements may be added.
81 This implementation always throws an UnsupportedOperationException.
83 o - element whose presence in this collection is to be ensured.
85 Returns: true if the collection changed as a result of the call.
86 *java.util.AbstractCollection.addAll(Collection)*
88 public boolean addAll(java.util.Collection c)
90 Adds all of the elements in the specified collection to this collection
91 (optional operation). The behavior of this operation is undefined if the
92 specified collection is modified while the operation is in progress. (This
93 implies that the behavior of this call is undefined if the specified collection
94 is this collection, and this collection is nonempty.)
96 This implementation iterates over the specified collection, and adds each
97 object returned by the iterator to this collection, in turn.
99 Note that this implementation will throw an UnsupportedOperationException
100 unless add is overridden (assuming the specified collection is non-empty).
102 c - collection whose elements are to be added to this collection.
104 Returns: true if this collection changed as a result of the call.
105 *java.util.AbstractCollection.clear()*
109 Removes all of the elements from this collection (optional operation). The
110 collection will be empty after this call returns (unless it throws an
113 This implementation iterates over this collection, removing each element using
114 the Iterator.remove operation. Most implementations will probably choose to
115 override this method for efficiency.
117 Note that this implementation will throw an UnsupportedOperationException if
118 the iterator returned by this collection's iterator method does not implement
119 the remove method and this collection is non-empty.
122 *java.util.AbstractCollection.contains(Object)*
124 public boolean contains(java.lang.Object o)
126 Returns true if this collection contains the specified element. More formally,
127 returns true if and only if this collection contains at least one element e
128 such that (o==null ? e==null : o.equals(e)).
130 This implementation iterates over the elements in the collection, checking each
131 element in turn for equality with the specified element.
133 o - object to be checked for containment in this collection.
135 Returns: true if this collection contains the specified element.
136 *java.util.AbstractCollection.containsAll(Collection)*
138 public boolean containsAll(java.util.Collection c)
140 Returns true if this collection contains all of the elements in the specified
143 This implementation iterates over the specified collection, checking each
144 element returned by the iterator in turn to see if it's contained in this
145 collection. If all elements are so contained true is returned, otherwise false.
147 c - collection to be checked for containment in this collection.
149 Returns: true if this collection contains all of the elements in the specified
151 *java.util.AbstractCollection.isEmpty()*
153 public boolean isEmpty()
155 Returns true if this collection contains no elements.
157 This implementation returns size() == 0.
160 Returns: true if this collection contains no elements.
161 *java.util.AbstractCollection.iterator()*
163 public abstract |java.util.Iterator| iterator()
165 Returns an iterator over the elements contained in this collection.
168 Returns: an iterator over the elements contained in this collection.
169 *java.util.AbstractCollection.remove(Object)*
171 public boolean remove(java.lang.Object o)
173 Removes a single instance of the specified element from this collection, if it
174 is present (optional operation). More formally, removes an element e such that
175 (o==null ? e==null : o.equals(e)), if the collection contains one or more such
176 elements. Returns true if the collection contained the specified element (or
177 equivalently, if the collection changed as a result of the call).
179 This implementation iterates over the collection looking for the specified
180 element. If it finds the element, it removes the element from the collection
181 using the iterator's remove method.
183 Note that this implementation throws an UnsupportedOperationException if the
184 iterator returned by this collection's iterator method does not implement the
185 remove method and this collection contains the specified object.
187 o - element to be removed from this collection, if present.
189 Returns: true if the collection contained the specified element.
190 *java.util.AbstractCollection.removeAll(Collection)*
192 public boolean removeAll(java.util.Collection c)
194 Removes from this collection all of its elements that are contained in the
195 specified collection (optional operation).
197 This implementation iterates over this collection, checking each element
198 returned by the iterator in turn to see if it's contained in the specified
199 collection. If it's so contained, it's removed from this collection with the
200 iterator's remove method.
202 Note that this implementation will throw an UnsupportedOperationException if
203 the iterator returned by the iterator method does not implement the remove
204 method and this collection contains one or more elements in common with the
205 specified collection.
207 c - elements to be removed from this collection.
209 Returns: true if this collection changed as a result of the call.
210 *java.util.AbstractCollection.retainAll(Collection)*
212 public boolean retainAll(java.util.Collection c)
214 Retains only the elements in this collection that are contained in the
215 specified collection (optional operation). In other words, removes from this
216 collection all of its elements that are not contained in the specified
219 This implementation iterates over this collection, checking each element
220 returned by the iterator in turn to see if it's contained in the specified
221 collection. If it's not so contained, it's removed from this collection with
222 the iterator's remove method.
224 Note that this implementation will throw an UnsupportedOperationException if
225 the iterator returned by the iterator method does not implement the remove
226 method and this collection contains one or more elements not present in the
227 specified collection.
229 c - elements to be retained in this collection.
231 Returns: true if this collection changed as a result of the call.
232 *java.util.AbstractCollection.size()*
234 public abstract int size()
236 Returns the number of elements in this collection. If the collection contains
237 more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
240 Returns: the number of elements in this collection.
241 *java.util.AbstractCollection.toArray()*
243 public |java.lang.Object| toArray()
245 Returns an array containing all of the elements in this collection. If the
246 collection makes any guarantees as to what order its elements are returned by
247 its iterator, this method must return the elements in the same order. The
248 returned array will be "safe" in that no references to it are maintained by the
249 collection. (In other words, this method must allocate a new array even if the
250 collection is backed by an Array). The caller is thus free to modify the
253 This implementation allocates the array to be returned, and iterates over the
254 elements in the collection, storing each object reference in the next
255 consecutive element of the array, starting with element 0.
258 Returns: an array containing all of the elements in this collection.
259 *java.util.AbstractCollection.toArray(T[])*
261 public |java.lang.Object| toArray(java.lang.Object[] a)
263 Returns an array containing all of the elements in this collection; the runtime
264 type of the returned array is that of the specified array. If the collection
265 fits in the specified array, it is returned therein. Otherwise, a new array is
266 allocated with the runtime type of the specified array and the size of this
269 If the collection fits in the specified array with room to spare (i.e., the
270 array has more elements than the collection), the element in the array
271 immediately following the end of the collection is set to null. This is useful
272 in determining the length of the collection only if the caller knows that the
273 collection does not contain any null elements.)
275 If this collection makes any guarantees as to what order its elements are
276 returned by its iterator, this method must return the elements in the same
279 This implementation checks if the array is large enough to contain the
280 collection; if not, it allocates a new array of the correct size and type
281 (using reflection). Then, it iterates over the collection, storing each object
282 reference in the next consecutive element of the array, starting with element
283 0. If the array is larger than the collection, a null is stored in the first
284 location after the end of the collection.
286 a - the array into which the elements of the collection are to be stored, if it is
287 big enough; otherwise, a new array of the same runtime type is allocated
290 Returns: an array containing the elements of the collection.
291 *java.util.AbstractCollection.toString()*
293 public |java.lang.String| toString()
295 Returns a string representation of this collection. The string representation
296 consists of a list of the collection's elements in the order they are returned
297 by its iterator, enclosed in square brackets ("[]"). Adjacent elements are
298 separated by the characters ", " (comma and space). Elements are converted to
299 strings as by String.valueOf(Object).
301 This implementation creates an empty string buffer, appends a left square
302 bracket, and iterates over the collection appending the string representation
303 of each element in turn. After appending each element except the last, the
304 string ", " is appended. Finally a right bracket is appended. A string is
305 obtained from the string buffer, and returned.
308 Returns: a string representation of this collection.