1 /*
2 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle 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 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 */
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> it = iterator();
100 if (o==null) {
101 while (it.hasNext())
102 if (it.next()==null)
103 return true;
104 } else {
105 while (it.hasNext())
106 if (o.equals(it.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 @SuppressWarnings("unchecked")
174 public <T> T[] toArray(T[] a) {
175 // Estimate size of array; be prepared to see more or fewer elements
176 int size = size();
177 T[] r = a.length >= size ? a :
178 (T[])java.lang.reflect.Array
179 .newInstance(a.getClass().getComponentType(), size);
180 Iterator<E> it = iterator();
181
182 for (int i = 0; i < r.length; i++) {
183 if (! it.hasNext()) { // fewer elements than expected
184 if (a != r)
185 return Arrays.copyOf(r, i);
186 r[i] = null; // null-terminate
187 return r;
188 }
189 r[i] = (T)it.next();
190 }
191 return it.hasNext() ? finishToArray(r, it) : r;
192 }
193
194 /**
195 * The maximum size of array to allocate.
196 * Some VMs reserve some header words in an array.
197 * Attempts to allocate larger arrays may result in
198 * OutOfMemoryError: Requested array size exceeds VM limit
199 */
200 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
201
202 /**
203 * Reallocates the array being used within toArray when the iterator
204 * returned more elements than expected, and finishes filling it from
205 * the iterator.
206 *
207 * @param r the array, replete with previously stored elements
208 * @param it the in-progress iterator over this collection
209 * @return array containing the elements in the given array, plus any
210 * further elements returned by the iterator, trimmed to size
211 */
212 @SuppressWarnings("unchecked")
213 private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
214 int i = r.length;
215 while (it.hasNext()) {
216 int cap = r.length;
217 if (i == cap) {
218 int newCap = cap + (cap >> 1) + 1;
219 // overflow-conscious code
220 if (newCap - MAX_ARRAY_SIZE > 0)
221 newCap = hugeCapacity(cap + 1);
222 r = Arrays.copyOf(r, newCap);
223 }
224 r[i++] = (T)it.next();
225 }
226 // trim if overallocated
227 return (i == r.length) ? r : Arrays.copyOf(r, i);
228 }
229
230 private static int hugeCapacity(int minCapacity) {
231 if (minCapacity < 0) // overflow
232 throw new OutOfMemoryError
233 ("Required array size too large");
234 return (minCapacity > MAX_ARRAY_SIZE) ?
235 Integer.MAX_VALUE :
236 MAX_ARRAY_SIZE;
237 }
238
239 // Modification Operations
240
241 /**
242 * {@inheritDoc}
243 *
244 * <p>This implementation always throws an
245 * <tt>UnsupportedOperationException</tt>.
246 *
247 * @throws UnsupportedOperationException {@inheritDoc}
248 * @throws ClassCastException {@inheritDoc}
249 * @throws NullPointerException {@inheritDoc}
250 * @throws IllegalArgumentException {@inheritDoc}
251 * @throws IllegalStateException {@inheritDoc}
252 */
253 public boolean add(E e) {
254 throw new UnsupportedOperationException();
255 }
256
257 /**
258 * {@inheritDoc}
259 *
260 * <p>This implementation iterates over the collection looking for the
261 * specified element. If it finds the element, it removes the element
262 * from the collection using the iterator's remove method.
263 *
264 * <p>Note that this implementation throws an
265 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
266 * collection's iterator method does not implement the <tt>remove</tt>
267 * method and this collection contains the specified object.
268 *
269 * @throws UnsupportedOperationException {@inheritDoc}
270 * @throws ClassCastException {@inheritDoc}
271 * @throws NullPointerException {@inheritDoc}
272 */
273 public boolean remove(Object o) {
274 Iterator<E> it = iterator();
275 if (o==null) {
276 while (it.hasNext()) {
277 if (it.next()==null) {
278 it.remove();
279 return true;
280 }
281 }
282 } else {
283 while (it.hasNext()) {
284 if (o.equals(it.next())) {
285 it.remove();
286 return true;
287 }
288 }
289 }
290 return false;
291 }
292
293
294 // Bulk Operations
295
296 /**
297 * {@inheritDoc}
298 *
299 * <p>This implementation iterates over the specified collection,
300 * checking each element returned by the iterator in turn to see
301 * if it's contained in this collection. If all elements are so
302 * contained <tt>true</tt> is returned, otherwise <tt>false</tt>.
303 *
304 * @throws ClassCastException {@inheritDoc}
305 * @throws NullPointerException {@inheritDoc}
306 * @see #contains(Object)
307 */
308 public boolean containsAll(Collection<?> c) {
309 for (Object e : c)
310 if (!contains(e))
311 return false;
312 return true;
313 }
314
315 /**
316 * {@inheritDoc}
317 *
318 * <p>This implementation iterates over the specified collection, and adds
319 * each object returned by the iterator to this collection, in turn.
320 *
321 * <p>Note that this implementation will throw an
322 * <tt>UnsupportedOperationException</tt> unless <tt>add</tt> is
323 * overridden (assuming the specified collection is non-empty).
324 *
325 * @throws UnsupportedOperationException {@inheritDoc}
326 * @throws ClassCastException {@inheritDoc}
327 * @throws NullPointerException {@inheritDoc}
328 * @throws IllegalArgumentException {@inheritDoc}
329 * @throws IllegalStateException {@inheritDoc}
330 *
331 * @see #add(Object)
332 */
333 public boolean addAll(Collection<? extends E> c) {
334 boolean modified = false;
335 for (E e : c)
336 if (add(e))
337 modified = true;
338 return modified;
339 }
340
341 /**
342 * {@inheritDoc}
343 *
344 * <p>This implementation iterates over this collection, checking each
345 * element returned by the iterator in turn to see if it's contained
346 * in the specified collection. If it's so contained, it's removed from
347 * this collection with the iterator's <tt>remove</tt> method.
348 *
349 * <p>Note that this implementation will throw an
350 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
351 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
352 * and this collection contains one or more elements in common with the
353 * specified collection.
354 *
355 * @throws UnsupportedOperationException {@inheritDoc}
356 * @throws ClassCastException {@inheritDoc}
357 * @throws NullPointerException {@inheritDoc}
358 *
359 * @see #remove(Object)
360 * @see #contains(Object)
361 */
362 public boolean removeAll(Collection<?> c) {
363 boolean modified = false;
364 Iterator<?> it = iterator();
365 while (it.hasNext()) {
366 if (c.contains(it.next())) {
367 it.remove();
368 modified = true;
369 }
370 }
371 return modified;
372 }
373
374 /**
375 * {@inheritDoc}
376 *
377 * <p>This implementation iterates over this collection, checking each
378 * element returned by the iterator in turn to see if it's contained
379 * in the specified collection. If it's not so contained, it's removed
380 * from this collection with the iterator's <tt>remove</tt> method.
381 *
382 * <p>Note that this implementation will throw an
383 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
384 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
385 * and this collection contains one or more elements not present in the
386 * specified collection.
387 *
388 * @throws UnsupportedOperationException {@inheritDoc}
389 * @throws ClassCastException {@inheritDoc}
390 * @throws NullPointerException {@inheritDoc}
391 *
392 * @see #remove(Object)
393 * @see #contains(Object)
394 */
395 public boolean retainAll(Collection<?> c) {
396 boolean modified = false;
397 Iterator<E> it = iterator();
398 while (it.hasNext()) {
399 if (!c.contains(it.next())) {
400 it.remove();
401 modified = true;
402 }
403 }
404 return modified;
405 }
406
407 /**
408 * {@inheritDoc}
409 *
410 * <p>This implementation iterates over this collection, removing each
411 * element using the <tt>Iterator.remove</tt> operation. Most
412 * implementations will probably choose to override this method for
413 * efficiency.
414 *
415 * <p>Note that this implementation will throw an
416 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
417 * collection's <tt>iterator</tt> method does not implement the
418 * <tt>remove</tt> method and this collection is non-empty.
419 *
420 * @throws UnsupportedOperationException {@inheritDoc}
421 */
422 public void clear() {
423 Iterator<E> it = iterator();
424 while (it.hasNext()) {
425 it.next();
426 it.remove();
427 }
428 }
429
430
431 // String conversion
432
433 /**
434 * Returns a string representation of this collection. The string
435 * representation consists of a list of the collection's elements in the
436 * order they are returned by its iterator, enclosed in square brackets
437 * (<tt>"[]"</tt>). Adjacent elements are separated by the characters
438 * <tt>", "</tt> (comma and space). Elements are converted to strings as
439 * by {@link String#valueOf(Object)}.
440 *
441 * @return a string representation of this collection
442 */
443 public String toString() {
444 Iterator<E> it = iterator();
445 if (! it.hasNext())
446 return "[]";
447
448 StringBuilder sb = new StringBuilder();
449 sb.append('[');
450 for (;;) {
451 E e = it.next();
452 sb.append(e == this ? "(this Collection)" : e);
453 if (! it.hasNext())
454 return sb.append(']').toString();
455 sb.append(',').append(' ');
456 }
457 }
458
459 }