1 /*
2 * Copyright (c) 1997, 2006, 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 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 * The maximum size of array to allocate.
195 * Some VMs reserve some header words in an array.
196 * Attempts to allocate larger arrays may result in
197 * OutOfMemoryError: Requested array size exceeds VM limit
198 */
199 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
200
201 /**
202 * Reallocates the array being used within toArray when the iterator
203 * returned more elements than expected, and finishes filling it from
204 * the iterator.
205 *
206 * @param r the array, replete with previously stored elements
207 * @param it the in-progress iterator over this collection
208 * @return array containing the elements in the given array, plus any
209 * further elements returned by the iterator, trimmed to size
210 */
211 private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
212 int i = r.length;
213 while (it.hasNext()) {
214 int cap = r.length;
215 if (i == cap) {
216 int newCap = cap + (cap >> 1) + 1;
217 // overflow-conscious code
218 if (newCap - MAX_ARRAY_SIZE > 0)
219 newCap = hugeCapacity(cap + 1);
220 r = Arrays.copyOf(r, newCap);
221 }
222 r[i++] = (T)it.next();
223 }
224 // trim if overallocated
225 return (i == r.length) ? r : Arrays.copyOf(r, i);
226 }
227
228 private static int hugeCapacity(int minCapacity) {
229 if (minCapacity < 0) // overflow
230 throw new OutOfMemoryError
231 ("Required array size too large");
232 return (minCapacity > MAX_ARRAY_SIZE) ?
233 Integer.MAX_VALUE :
234 MAX_ARRAY_SIZE;
235 }
236
237 // Modification Operations
238
239 /**
240 * {@inheritDoc}
241 *
242 * <p>This implementation always throws an
243 * <tt>UnsupportedOperationException</tt>.
244 *
245 * @throws UnsupportedOperationException {@inheritDoc}
246 * @throws ClassCastException {@inheritDoc}
247 * @throws NullPointerException {@inheritDoc}
248 * @throws IllegalArgumentException {@inheritDoc}
249 * @throws IllegalStateException {@inheritDoc}
250 */
251 public boolean add(E e) {
252 throw new UnsupportedOperationException();
253 }
254
255 /**
256 * {@inheritDoc}
257 *
258 * <p>This implementation iterates over the collection looking for the
259 * specified element. If it finds the element, it removes the element
260 * from the collection using the iterator's remove method.
261 *
262 * <p>Note that this implementation throws an
263 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
264 * collection's iterator method does not implement the <tt>remove</tt>
265 * method and this collection contains the specified object.
266 *
267 * @throws UnsupportedOperationException {@inheritDoc}
268 * @throws ClassCastException {@inheritDoc}
269 * @throws NullPointerException {@inheritDoc}
270 */
271 public boolean remove(Object o) {
272 Iterator<E> it = iterator();
273 if (o==null) {
274 while (it.hasNext()) {
275 if (it.next()==null) {
276 it.remove();
277 return true;
278 }
279 }
280 } else {
281 while (it.hasNext()) {
282 if (o.equals(it.next())) {
283 it.remove();
284 return true;
285 }
286 }
287 }
288 return false;
289 }
290
291
292 // Bulk Operations
293
294 /**
295 * {@inheritDoc}
296 *
297 * <p>This implementation iterates over the specified collection,
298 * checking each element returned by the iterator in turn to see
299 * if it's contained in this collection. If all elements are so
300 * contained <tt>true</tt> is returned, otherwise <tt>false</tt>.
301 *
302 * @throws ClassCastException {@inheritDoc}
303 * @throws NullPointerException {@inheritDoc}
304 * @see #contains(Object)
305 */
306 public boolean containsAll(Collection<?> c) {
307 for (Object e : c)
308 if (!contains(e))
309 return false;
310 return true;
311 }
312
313 /**
314 * {@inheritDoc}
315 *
316 * <p>This implementation iterates over the specified collection, and adds
317 * each object returned by the iterator to this collection, in turn.
318 *
319 * <p>Note that this implementation will throw an
320 * <tt>UnsupportedOperationException</tt> unless <tt>add</tt> is
321 * overridden (assuming the specified collection is non-empty).
322 *
323 * @throws UnsupportedOperationException {@inheritDoc}
324 * @throws ClassCastException {@inheritDoc}
325 * @throws NullPointerException {@inheritDoc}
326 * @throws IllegalArgumentException {@inheritDoc}
327 * @throws IllegalStateException {@inheritDoc}
328 *
329 * @see #add(Object)
330 */
331 public boolean addAll(Collection<? extends E> c) {
332 boolean modified = false;
333 for (E e : c)
334 if (add(e))
335 modified = true;
336 return modified;
337 }
338
339 /**
340 * {@inheritDoc}
341 *
342 * <p>This implementation iterates over this collection, checking each
343 * element returned by the iterator in turn to see if it's contained
344 * in the specified collection. If it's so contained, it's removed from
345 * this collection with the iterator's <tt>remove</tt> method.
346 *
347 * <p>Note that this implementation will throw an
348 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
349 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
350 * and this collection contains one or more elements in common with the
351 * specified collection.
352 *
353 * @throws UnsupportedOperationException {@inheritDoc}
354 * @throws ClassCastException {@inheritDoc}
355 * @throws NullPointerException {@inheritDoc}
356 *
357 * @see #remove(Object)
358 * @see #contains(Object)
359 */
360 public boolean removeAll(Collection<?> c) {
361 boolean modified = false;
362 Iterator<?> it = iterator();
363 while (it.hasNext()) {
364 if (c.contains(it.next())) {
365 it.remove();
366 modified = true;
367 }
368 }
369 return modified;
370 }
371
372 /**
373 * {@inheritDoc}
374 *
375 * <p>This implementation iterates over this collection, checking each
376 * element returned by the iterator in turn to see if it's contained
377 * in the specified collection. If it's not so contained, it's removed
378 * from this collection with the iterator's <tt>remove</tt> method.
379 *
380 * <p>Note that this implementation will throw an
381 * <tt>UnsupportedOperationException</tt> if the iterator returned by the
382 * <tt>iterator</tt> method does not implement the <tt>remove</tt> method
383 * and this collection contains one or more elements not present in the
384 * specified collection.
385 *
386 * @throws UnsupportedOperationException {@inheritDoc}
387 * @throws ClassCastException {@inheritDoc}
388 * @throws NullPointerException {@inheritDoc}
389 *
390 * @see #remove(Object)
391 * @see #contains(Object)
392 */
393 public boolean retainAll(Collection<?> c) {
394 boolean modified = false;
395 Iterator<E> it = iterator();
396 while (it.hasNext()) {
397 if (!c.contains(it.next())) {
398 it.remove();
399 modified = true;
400 }
401 }
402 return modified;
403 }
404
405 /**
406 * {@inheritDoc}
407 *
408 * <p>This implementation iterates over this collection, removing each
409 * element using the <tt>Iterator.remove</tt> operation. Most
410 * implementations will probably choose to override this method for
411 * efficiency.
412 *
413 * <p>Note that this implementation will throw an
414 * <tt>UnsupportedOperationException</tt> if the iterator returned by this
415 * collection's <tt>iterator</tt> method does not implement the
416 * <tt>remove</tt> method and this collection is non-empty.
417 *
418 * @throws UnsupportedOperationException {@inheritDoc}
419 */
420 public void clear() {
421 Iterator<E> it = iterator();
422 while (it.hasNext()) {
423 it.next();
424 it.remove();
425 }
426 }
427
428
429 // String conversion
430
431 /**
432 * Returns a string representation of this collection. The string
433 * representation consists of a list of the collection's elements in the
434 * order they are returned by its iterator, enclosed in square brackets
435 * (<tt>"[]"</tt>). Adjacent elements are separated by the characters
436 * <tt>", "</tt> (comma and space). Elements are converted to strings as
437 * by {@link String#valueOf(Object)}.
438 *
439 * @return a string representation of this collection
440 */
441 public String toString() {
442 Iterator<E> it = iterator();
443 if (! it.hasNext())
444 return "[]";
445
446 StringBuilder sb = new StringBuilder();
447 sb.append('[');
448 for (;;) {
449 E e = it.next();
450 sb.append(e == this ? "(this Collection)" : e);
451 if (! it.hasNext())
452 return sb.append(']').toString();
453 sb.append(',').append(' ');
454 }
455 }
456
457 }