1 /*
2 * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * 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 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package java.util;
27
28 /**
29 * This class provides a skeletal implementation of the <tt>Collection</tt>
30 * interface, to minimize the effort required to implement this interface. <p>
31 *
32 * To implement an unmodifiable collection, the programmer needs only to
33 * extend this class and provide implementations for the <tt>iterator</tt> and
34 * <tt>size</tt> methods. (The iterator returned by the <tt>iterator</tt>
35 * method must implement <tt>hasNext</tt> and <tt>next</tt>.)<p>
36 *
37 * To implement a modifiable collection, the programmer must additionally
38 * override this class's <tt>add</tt> method (which otherwise throws an
39 * <tt>UnsupportedOperationException</tt>), and the iterator returned by the
40 * <tt>iterator</tt> method must additionally implement its <tt>remove</tt>
41 * method.<p>
42 *
43 * The programmer should generally provide a void (no argument) and
44 * <tt>Collection</tt> constructor, as per the recommendation in the
45 * <tt>Collection</tt> interface specification.<p>
46 *
47 * The documentation for each non-abstract method in this class describes its
48 * implementation in detail. Each of these methods may be overridden if
49 * the collection being implemented admits a more efficient implementation.<p>
50 *
51 * This class is a member of the
52 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
53 * Java Collections Framework</a>.
54 *
55 * @author Josh Bloch
56 * @author Neal Gafter
57 * @see Collection
58 * @since 1.2
59 */
60
61 public abstract class AbstractCollection<E> implements Collection<E> {
62 /**
63 * Sole constructor. (For invocation by subclass constructors, typically
64 * implicit.)
65 */
66 protected AbstractCollection() {
67 }
68
69 // Query Operations
70
71 /**
72 * Returns an iterator over the elements contained in this collection.
73 *
74 * @return an iterator over the elements contained in this collection
75 */
76 public abstract Iterator<E> iterator();
77
78 public abstract int size();
79
80 /**
81 * {@inheritDoc}
82 *
83 * <p>This implementation returns <tt>size() == 0</tt>.
84 */
85 public boolean isEmpty() {
86 return size() == 0;
87 }
88
89 /**
90 * {@inheritDoc}
91 *
92 * <p>This implementation iterates over the elements in the collection,
93 * checking each element in turn for equality with the specified element.
94 *
95 * @throws ClassCastException {@inheritDoc}
96 * @throws NullPointerException {@inheritDoc}
97 */
98 public boolean contains(Object o) {
99 Iterator<E> e = iterator();
100 if (o==null) {
101 while (e.hasNext())
102 if (e.next()==null)
103 return true;
104 } else {
105 while (e.hasNext())
106 if (o.equals(e.next()))
107 return true;
108 }
109 return false;
110 }
111
112 /**
113 * {@inheritDoc}
114 *
115 * <p>This implementation returns an array containing all the elements
116 * returned by this collection's iterator, in the same order, stored in
117 * consecutive elements of the array, starting with index {@code 0}.
118 * The length of the returned array is equal to the number of elements
119 * returned by the iterator, even if the size of this collection changes
120 * during iteration, as might happen if the collection permits
121 * concurrent modification during iteration. The {@code size} method is
122 * called only as an optimization hint; the correct result is returned
123 * even if the iterator returns a different number of elements.
124 *
125 * <p>This method is equivalent to:
126 *
127 * <pre> {@code
128 * List<E> list = new ArrayList<E>(size());
129 * for (E e : this)
130 * list.add(e);
131 * return list.toArray();
132 * }</pre>
133 */
134 public Object[] toArray() {
135 // Estimate size of array; be prepared to see more or fewer elements
136 Object[] r = new Object[size()];
137 Iterator<E> it = iterator();
138 for (int i = 0; i < r.length; i++) {
139 if (! it.hasNext()) // fewer elements than expected
140 return Arrays.copyOf(r, i);
141 r[i] = it.next();
142 }
143 return it.hasNext() ? finishToArray(r, it) : r;
144 }
145
146 /**
147 * {@inheritDoc}
148 *
149 * <p>This implementation returns an array containing all the elements
150 * returned by this collection's iterator in the same order, stored in
151 * consecutive elements of the array, starting with index {@code 0}.
152 * If the number of elements returned by the iterator is too large to
153 * fit into the specified array, then the elements are returned in a
154 * newly allocated array with length equal to the number of elements
155 * returned by the iterator, even if the size of this collection
156 * changes during iteration, as might happen if the collection permits
157 * concurrent modification during iteration. The {@code size} method is
158 * called only as an optimization hint; the correct result is returned
159 * even if the iterator returns a different number of elements.
160 *
161 * <p>This method is equivalent to:
162 *
163 * <pre> {@code
164 * List<E> list = new ArrayList<E>(size());
165 * for (E e : this)
166 * list.add(e);
167 * return list.toArray(a);
168 * }</pre>
169 *
170 * @throws ArrayStoreException {@inheritDoc}
171 * @throws NullPointerException {@inheritDoc}
172 */
173 public <T> T[] toArray(T[] a) {
174 // Estimate size of array; be prepared to see more or fewer elements
175 int size = size();
176 T[] r = a.length >= size ? a :
177 (T[])java.lang.reflect.Array
178 .newInstance(a.getClass().getComponentType(), size);
179 Iterator<E> it = iterator();
180
181 for (int i = 0; i < r.length; i++) {
182 if (! it.hasNext()) { // fewer elements than expected
183 if (a != r)
184 return Arrays.copyOf(r, i);
185 r[i] = null; // null-terminate
186 return r;
187 }
188 r[i] = (T)it.next();
189 }
190 return it.hasNext() ? finishToArray(r, it) : r;
191 }
192
193 /**
194 * Reallocates the array being used within toArray when the iterator
195 * returned more elements than expected, and finishes filling it from
196 * the iterator.
197 *
198 * @param r the array, replete with previously stored elements
199 * @param it the in-progress iterator over this collection
200 * @return array containing the elements in the given array, plus any
201 * further elements returned by the iterator, trimmed to size
202 */
203 private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
204 int i = r.length;
205 while (it.hasNext()) {
206 int cap = r.length;
207 if (i == cap) {
208 int newCap = ((cap / 2) + 1) * 3;
209 if (newCap <= cap) { // integer overflow
210 if (cap == Integer.MAX_VALUE)
211 throw new OutOfMemoryError
212 ("Required array size too large");
213 newCap = Integer.MAX_VALUE;
214 }
215 r = Arrays.copyOf(r, newCap);
216 }
217 r[i++] = (T)it.next();
218 }
219 // trim if overallocated
220 return (i == r.length) ? r : Arrays.copyOf(r, i);
221 }
222
223 // Modification Operations
224
225 /**
226 * {@inheritDoc}
227 *
228 * <p>This implementation always throws an
229 * <tt>UnsupportedOperationException</tt>.
230 *
231 * @throws UnsupportedOperationException {@inheritDoc}
232 * @throws ClassCastException {@inheritDoc}
233 * @throws NullPointerException {@inheritDoc}
234 * @throws IllegalArgumentException {@inheritDoc}
235 * @throws IllegalStateException {@inheritDoc}
236 */
237 public boolean add(E e) {
238 throw new UnsupportedOperationException();
239 }
240
241 /**
242 * {@inheritDoc}
243 *
244 * <p>This implementation iterates over the collection looking for the
245 * specified element. If it finds the element, it removes the element
246 * from the collection using the iterator's remove method.
247 *
248 * <p>Note that this implementation throws an
249 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
250 * collection's iterator method does not implement the <tt>remove</tt>
251 * method and this collection contains the specified object.
252 *
253 * @throws UnsupportedOperationException {@inheritDoc}
254 * @throws ClassCastException {@inheritDoc}
255 * @throws NullPointerException {@inheritDoc}
256 */
257 public boolean remove(Object o) {
258 Iterator<E> e = iterator();
259 if (o==null) {
260 while (e.hasNext()) {
261 if (e.next()==null) {
262 e.remove();
263 return true;
264 }
265 }
266 } else {
267 while (e.hasNext()) {
268 if (o.equals(e.next())) {
269 e.remove();
270 return true;
271 }
272 }
273 }
274 return false;
275 }
276
277
278 // Bulk Operations
279
280 /**
281 * {@inheritDoc}
282 *
283 * <p>This implementation iterates over the specified collection,
284 * checking each element returned by the iterator in turn to see
285 * if it's contained in this collection. If all elements are so
286 * contained <tt>true</tt> is returned, otherwise <tt>false</tt>.
287 *
288 * @throws ClassCastException {@inheritDoc}
289 * @throws NullPointerException {@inheritDoc}
290 * @see #contains(Object)
291 */
292 public boolean containsAll(Collection<?> c) {
293 Iterator<?> e = c.iterator();
294 while (e.hasNext())
295 if (!contains(e.next()))
296 return false;
297 return true;
298 }
299
300 /**
301 * {@inheritDoc}
302 *
303 * <p>This implementation iterates over the specified collection, and adds
304 * each object returned by the iterator to this collection, in turn.
305 *
306 * <p>Note that this implementation will throw an
307 * <tt>UnsupportedOperationException</tt> unless <tt>add</tt> is
308 * overridden (assuming the specified collection is non-empty).
309 *
310 * @throws UnsupportedOperationException {@inheritDoc}
311 * @throws ClassCastException {@inheritDoc}
312 * @throws NullPointerException {@inheritDoc}
313 * @throws IllegalArgumentException {@inheritDoc}
314 * @throws IllegalStateException {@inheritDoc}
315 *
316 * @see #add(Object)
317 */
318 public boolean addAll(Collection<? extends E> c) {
319 boolean modified = false;
320 Iterator<? extends E> e = c.iterator();
321 while (e.hasNext()) {
322 if (add(e.next()))
323 modified = true;
324 }
325 return modified;
326 }
327
328 /**
329 * {@inheritDoc}
330 *
331 * <p>This implementation iterates over this collection, checking each
332 * element returned by the iterator in turn to see if it's contained
333 * in the specified collection. If it's so contained, it's removed from
334 * this collection with the iterator's <tt>remove</tt> method.
335 *
336 * <p>Note that this implementation will throw an
337 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
338 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
339 * and this collection contains one or more elements in common with the
340 * specified collection.
341 *
342 * @throws UnsupportedOperationException {@inheritDoc}
343 * @throws ClassCastException {@inheritDoc}
344 * @throws NullPointerException {@inheritDoc}
345 *
346 * @see #remove(Object)
347 * @see #contains(Object)
348 */
349 public boolean removeAll(Collection<?> c) {
350 boolean modified = false;
351 Iterator<?> e = iterator();
352 while (e.hasNext()) {
353 if (c.contains(e.next())) {
354 e.remove();
355 modified = true;
356 }
357 }
358 return modified;
359 }
360
361 /**
362 * {@inheritDoc}
363 *
364 * <p>This implementation iterates over this collection, checking each
365 * element returned by the iterator in turn to see if it's contained
366 * in the specified collection. If it's not so contained, it's removed
367 * from this collection with the iterator's <tt>remove</tt> method.
368 *
369 * <p>Note that this implementation will throw an
370 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
371 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
372 * and this collection contains one or more elements not present in the
373 * specified collection.
374 *
375 * @throws UnsupportedOperationException {@inheritDoc}
376 * @throws ClassCastException {@inheritDoc}
377 * @throws NullPointerException {@inheritDoc}
378 *
379 * @see #remove(Object)
380 * @see #contains(Object)
381 */
382 public boolean retainAll(Collection<?> c) {
383 boolean modified = false;
384 Iterator<E> e = iterator();
385 while (e.hasNext()) {
386 if (!c.contains(e.next())) {
387 e.remove();
388 modified = true;
389 }
390 }
391 return modified;
392 }
393
394 /**
395 * {@inheritDoc}
396 *
397 * <p>This implementation iterates over this collection, removing each
398 * element using the <tt>Iterator.remove</tt> operation. Most
399 * implementations will probably choose to override this method for
400 * efficiency.
401 *
402 * <p>Note that this implementation will throw an
403 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
404 * collection's <tt>iterator</tt> method does not implement the
405 * <tt>remove</tt> method and this collection is non-empty.
406 *
407 * @throws UnsupportedOperationException {@inheritDoc}
408 */
409 public void clear() {
410 Iterator<E> e = iterator();
411 while (e.hasNext()) {
412 e.next();
413 e.remove();
414 }
415 }
416
417
418 // String conversion
419
420 /**
421 * Returns a string representation of this collection. The string
422 * representation consists of a list of the collection's elements in the
423 * order they are returned by its iterator, enclosed in square brackets
424 * (<tt>"[]"</tt>). Adjacent elements are separated by the characters
425 * <tt>", "</tt> (comma and space). Elements are converted to strings as
426 * by {@link String#valueOf(Object)}.
427 *
428 * @return a string representation of this collection
429 */
430 public String toString() {
431 Iterator<E> i = iterator();
432 if (! i.hasNext())
433 return "[]";
434
435 StringBuilder sb = new StringBuilder();
436 sb.append('[');
437 for (;;) {
438 E e = i.next();
439 sb.append(e == this ? "(this Collection)" : e);
440 if (! i.hasNext())
441 return sb.append(']').toString();
442 sb.append(", ");
443 }
444 }
445
446 }
Save This Page