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1 : dl 1.1 /*
2 :     * Written by Doug Lea and Josh Bloch with assistance from members of
3 :     * JCP JSR-166 Expert Group and released to the public domain, as explained
4 : jsr166 1.20 * at http://creativecommons.org/publicdomain/zero/1.0/
5 : dl 1.1 */
6 :    
7 :     package java.util;
8 :    
9 :     /**
10 :     * A linear collection that supports element insertion and removal at
11 :     * both ends. The name <i>deque</i> is short for "double ended queue"
12 : jsr166 1.22 * and is usually pronounced "deck". Most {@code Deque}
13 : dl 1.1 * implementations place no fixed limits on the number of elements
14 :     * they may contain, but this interface supports capacity-restricted
15 :     * deques as well as those with no fixed size limit.
16 :     *
17 :     * <p>This interface defines methods to access the elements at both
18 :     * ends of the deque. Methods are provided to insert, remove, and
19 :     * examine the element. Each of these methods exists in two forms:
20 :     * one throws an exception if the operation fails, the other returns a
21 : jsr166 1.22 * special value (either {@code null} or {@code false}, depending on
22 : dl 1.1 * the operation). The latter form of the insert operation is
23 :     * designed specifically for use with capacity-restricted
24 : jsr166 1.22 * {@code Deque} implementations; in most implementations, insert
25 : dl 1.1 * operations cannot fail.
26 :     *
27 : dl 1.3 * <p>The twelve methods described above are summarized in the
28 : jsr166 1.5 * following table:
29 : dl 1.3 *
30 : jsr166 1.7 * <table BORDER CELLPADDING=3 CELLSPACING=1>
31 : jsr166 1.24 * <caption>Summary of Deque methods</caption>
32 : dl 1.1 * <tr>
33 :     * <td></td>
34 :     * <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
35 :     * <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
36 :     * </tr>
37 :     * <tr>
38 :     * <td></td>
39 :     * <td ALIGN=CENTER><em>Throws exception</em></td>
40 : jsr166 1.8 * <td ALIGN=CENTER><em>Special value</em></td>
41 : dl 1.1 * <td ALIGN=CENTER><em>Throws exception</em></td>
42 : jsr166 1.8 * <td ALIGN=CENTER><em>Special value</em></td>
43 : dl 1.1 * </tr>
44 :     * <tr>
45 :     * <td><b>Insert</b></td>
46 : dl 1.26 * <td>{@link Deque#addFirst addFirst(e)}</td>
47 :     * <td>{@link Deque#offerFirst offerFirst(e)}</td>
48 :     * <td>{@link Deque#addLast addLast(e)}</td>
49 :     * <td>{@link Deque#offerLast offerLast(e)}</td>
50 : dl 1.1 * </tr>
51 :     * <tr>
52 :     * <td><b>Remove</b></td>
53 : dl 1.26 * <td>{@link Deque#removeFirst removeFirst()}</td>
54 :     * <td>{@link Deque#pollFirst pollFirst()}</td>
55 :     * <td>{@link Deque#removeLast removeLast()}</td>
56 :     * <td>{@link Deque#pollLast pollLast()}</td>
57 : dl 1.1 * </tr>
58 :     * <tr>
59 :     * <td><b>Examine</b></td>
60 : dl 1.26 * <td>{@link Deque#getFirst getFirst()}</td>
61 :     * <td>{@link Deque#peekFirst peekFirst()}</td>
62 :     * <td>{@link Deque#getLast getLast()}</td>
63 :     * <td>{@link Deque#peekLast peekLast()}</td>
64 : dl 1.1 * </tr>
65 :     * </table>
66 :     *
67 :     * <p>This interface extends the {@link Queue} interface. When a deque is
68 :     * used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
69 : dl 1.4 * added at the end of the deque and removed from the beginning. The methods
70 : jsr166 1.22 * inherited from the {@code Queue} interface are precisely equivalent to
71 :     * {@code Deque} methods as indicated in the following table:
72 : dl 1.1 *
73 : jsr166 1.7 * <table BORDER CELLPADDING=3 CELLSPACING=1>
74 : jsr166 1.24 * <caption>Comparison of Queue and Deque methods</caption>
75 : dl 1.1 * <tr>
76 : jsr166 1.22 * <td ALIGN=CENTER> <b>{@code Queue} Method</b></td>
77 :     * <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
78 : dl 1.1 * </tr>
79 :     * <tr>
80 : jsr166 1.8 * <td>{@link java.util.Queue#add add(e)}</td>
81 :     * <td>{@link #addLast addLast(e)}</td>
82 :     * </tr>
83 :     * <tr>
84 : dl 1.1 * <td>{@link java.util.Queue#offer offer(e)}</td>
85 :     * <td>{@link #offerLast offerLast(e)}</td>
86 : jsr166 1.5 * </tr>
87 :     * <tr>
88 : jsr166 1.8 * <td>{@link java.util.Queue#remove remove()}</td>
89 :     * <td>{@link #removeFirst removeFirst()}</td>
90 : jsr166 1.5 * </tr>
91 :     * <tr>
92 : dl 1.1 * <td>{@link java.util.Queue#poll poll()}</td>
93 :     * <td>{@link #pollFirst pollFirst()}</td>
94 : jsr166 1.5 * </tr>
95 :     * <tr>
96 : jsr166 1.8 * <td>{@link java.util.Queue#element element()}</td>
97 :     * <td>{@link #getFirst getFirst()}</td>
98 : jsr166 1.5 * </tr>
99 :     * <tr>
100 : dl 1.1 * <td>{@link java.util.Queue#peek peek()}</td>
101 :     * <td>{@link #peek peekFirst()}</td>
102 : jsr166 1.5 * </tr>
103 : dl 1.1 * </table>
104 :     *
105 :     * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
106 :     * interface should be used in preference to the legacy {@link Stack} class.
107 : dl 1.3 * When a deque is used as a stack, elements are pushed and popped from the
108 : dl 1.1 * beginning of the deque. Stack methods are precisely equivalent to
109 : jsr166 1.22 * {@code Deque} methods as indicated in the table below:
110 : dl 1.1 *
111 : jsr166 1.7 * <table BORDER CELLPADDING=3 CELLSPACING=1>
112 : jsr166 1.24 * <caption>Comparison of Stack and Deque methods</caption>
113 : dl 1.1 * <tr>
114 :     * <td ALIGN=CENTER> <b>Stack Method</b></td>
115 : jsr166 1.22 * <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
116 : dl 1.1 * </tr>
117 :     * <tr>
118 :     * <td>{@link #push push(e)}</td>
119 :     * <td>{@link #addFirst addFirst(e)}</td>
120 : jsr166 1.5 * </tr>
121 :     * <tr>
122 : dl 1.1 * <td>{@link #pop pop()}</td>
123 :     * <td>{@link #removeFirst removeFirst()}</td>
124 : jsr166 1.5 * </tr>
125 :     * <tr>
126 : dl 1.1 * <td>{@link #peek peek()}</td>
127 :     * <td>{@link #peekFirst peekFirst()}</td>
128 : jsr166 1.5 * </tr>
129 : dl 1.1 * </table>
130 :     *
131 :     * <p>Note that the {@link #peek peek} method works equally well when
132 :     * a deque is used as a queue or a stack; in either case, elements are
133 :     * drawn from the beginning of the deque.
134 :     *
135 : dl 1.2 * <p>This interface provides two methods to remove interior
136 : dl 1.1 * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
137 : jsr166 1.8 * {@link #removeLastOccurrence removeLastOccurrence}.
138 :     *
139 :     * <p>Unlike the {@link List} interface, this interface does not
140 :     * provide support for indexed access to elements.
141 : dl 1.1 *
142 : jsr166 1.22 * <p>While {@code Deque} implementations are not strictly required
143 : dl 1.1 * to prohibit the insertion of null elements, they are strongly
144 : jsr166 1.22 * encouraged to do so. Users of any {@code Deque} implementations
145 : dl 1.1 * that do allow null elements are strongly encouraged <i>not</i> to
146 :     * take advantage of the ability to insert nulls. This is so because
147 : jsr166 1.22 * {@code null} is used as a special return value by various methods
148 : dl 1.1 * to indicated that the deque is empty.
149 : dl 1.3 *
150 : jsr166 1.22 * <p>{@code Deque} implementations generally do not define
151 :     * element-based versions of the {@code equals} and {@code hashCode}
152 : dl 1.1 * methods, but instead inherit the identity-based versions from class
153 : jsr166 1.22 * {@code Object}.
154 : dl 1.1 *
155 :     * <p>This interface is a member of the <a
156 : jsr166 1.19 * href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
157 : dl 1.1 * Framework</a>.
158 :     *
159 :     * @author Doug Lea
160 :     * @author Josh Bloch
161 :     * @since 1.6
162 :     * @param <E> the type of elements held in this collection
163 :     */
164 :     public interface Deque<E> extends Queue<E> {
165 :     /**
166 : jsr166 1.8 * Inserts the specified element at the front of this deque if it is
167 : jsr166 1.25 * possible to do so immediately without violating capacity restrictions,
168 :     * throwing an {@code IllegalStateException} if no space is currently
169 :     * available. When using a capacity-restricted deque, it is generally
170 :     * preferable to use method {@link #offerFirst}.
171 : jsr166 1.8 *
172 :     * @param e the element to add
173 :     * @throws IllegalStateException if the element cannot be added at this
174 :     * time due to capacity restrictions
175 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
176 :     * prevents it from being added to this deque
177 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
178 :     * deque does not permit null elements
179 :     * @throws IllegalArgumentException if some property of the specified
180 :     * element prevents it from being added to this deque
181 :     */
182 :     void addFirst(E e);
183 :    
184 :     /**
185 : jsr166 1.13 * Inserts the specified element at the end of this deque if it is
186 : jsr166 1.25 * possible to do so immediately without violating capacity restrictions,
187 :     * throwing an {@code IllegalStateException} if no space is currently
188 :     * available. When using a capacity-restricted deque, it is generally
189 :     * preferable to use method {@link #offerLast}.
190 : jsr166 1.8 *
191 : jsr166 1.14 * <p>This method is equivalent to {@link #add}.
192 :     *
193 : jsr166 1.8 * @param e the element to add
194 :     * @throws IllegalStateException if the element cannot be added at this
195 :     * time due to capacity restrictions
196 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
197 :     * prevents it from being added to this deque
198 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
199 :     * deque does not permit null elements
200 :     * @throws IllegalArgumentException if some property of the specified
201 :     * element prevents it from being added to this deque
202 :     */
203 :     void addLast(E e);
204 :    
205 :     /**
206 : dl 1.3 * Inserts the specified element at the front of this deque unless it would
207 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
208 : jsr166 1.8 * this method is generally preferable to the {@link #addFirst} method,
209 :     * which can fail to insert an element only by throwing an exception.
210 : dl 1.1 *
211 : jsr166 1.8 * @param e the element to add
212 : jsr166 1.22 * @return {@code true} if the element was added to this deque, else
213 :     * {@code false}
214 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
215 :     * prevents it from being added to this deque
216 : dl 1.3 * @throws NullPointerException if the specified element is null and this
217 : jsr166 1.8 * deque does not permit null elements
218 :     * @throws IllegalArgumentException if some property of the specified
219 :     * element prevents it from being added to this deque
220 : dl 1.1 */
221 :     boolean offerFirst(E e);
222 :    
223 :     /**
224 : dl 1.4 * Inserts the specified element at the end of this deque unless it would
225 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
226 : jsr166 1.8 * this method is generally preferable to the {@link #addLast} method,
227 :     * which can fail to insert an element only by throwing an exception.
228 : dl 1.1 *
229 : jsr166 1.8 * @param e the element to add
230 : jsr166 1.22 * @return {@code true} if the element was added to this deque, else
231 :     * {@code false}
232 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
233 :     * prevents it from being added to this deque
234 : dl 1.3 * @throws NullPointerException if the specified element is null and this
235 : jsr166 1.8 * deque does not permit null elements
236 :     * @throws IllegalArgumentException if some property of the specified
237 :     * element prevents it from being added to this deque
238 : dl 1.1 */
239 :     boolean offerLast(E e);
240 :    
241 :     /**
242 : jsr166 1.8 * Retrieves and removes the first element of this deque. This method
243 : jsr166 1.15 * differs from {@link #pollFirst pollFirst} only in that it throws an
244 :     * exception if this deque is empty.
245 : dl 1.1 *
246 : jsr166 1.8 * @return the head of this deque
247 :     * @throws NoSuchElementException if this deque is empty
248 : dl 1.1 */
249 : jsr166 1.8 E removeFirst();
250 : dl 1.1
251 :     /**
252 : jsr166 1.8 * Retrieves and removes the last element of this deque. This method
253 : jsr166 1.15 * differs from {@link #pollLast pollLast} only in that it throws an
254 :     * exception if this deque is empty.
255 : dl 1.1 *
256 : jsr166 1.8 * @return the tail of this deque
257 :     * @throws NoSuchElementException if this deque is empty
258 : dl 1.1 */
259 : jsr166 1.8 E removeLast();
260 : dl 1.1
261 :     /**
262 : jsr166 1.8 * Retrieves and removes the first element of this deque,
263 : jsr166 1.22 * or returns {@code null} if this deque is empty.
264 : dl 1.1 *
265 : jsr166 1.22 * @return the head of this deque, or {@code null} if this deque is empty
266 : dl 1.1 */
267 :     E pollFirst();
268 :    
269 :     /**
270 : jsr166 1.8 * Retrieves and removes the last element of this deque,
271 : jsr166 1.22 * or returns {@code null} if this deque is empty.
272 : dl 1.1 *
273 : jsr166 1.22 * @return the tail of this deque, or {@code null} if this deque is empty
274 : dl 1.1 */
275 :     E pollLast();
276 :    
277 :     /**
278 : jsr166 1.8 * Retrieves, but does not remove, the first element of this deque.
279 : jsr166 1.16 *
280 : jsr166 1.15 * This method differs from {@link #peekFirst peekFirst} only in that it
281 :     * throws an exception if this deque is empty.
282 : dl 1.1 *
283 : jsr166 1.8 * @return the head of this deque
284 : dl 1.1 * @throws NoSuchElementException if this deque is empty
285 :     */
286 : jsr166 1.8 E getFirst();
287 : dl 1.1
288 :     /**
289 : jsr166 1.8 * Retrieves, but does not remove, the last element of this deque.
290 : jsr166 1.15 * This method differs from {@link #peekLast peekLast} only in that it
291 :     * throws an exception if this deque is empty.
292 : dl 1.1 *
293 : jsr166 1.8 * @return the tail of this deque
294 : dl 1.1 * @throws NoSuchElementException if this deque is empty
295 :     */
296 : jsr166 1.8 E getLast();
297 : dl 1.1
298 :     /**
299 :     * Retrieves, but does not remove, the first element of this deque,
300 : jsr166 1.22 * or returns {@code null} if this deque is empty.
301 : dl 1.1 *
302 : jsr166 1.22 * @return the head of this deque, or {@code null} if this deque is empty
303 : dl 1.1 */
304 :     E peekFirst();
305 :    
306 :     /**
307 :     * Retrieves, but does not remove, the last element of this deque,
308 : jsr166 1.22 * or returns {@code null} if this deque is empty.
309 : dl 1.1 *
310 : jsr166 1.22 * @return the tail of this deque, or {@code null} if this deque is empty
311 : dl 1.1 */
312 :     E peekLast();
313 :    
314 :     /**
315 : jsr166 1.8 * Removes the first occurrence of the specified element from this deque.
316 :     * If the deque does not contain the element, it is unchanged.
317 : jsr166 1.22 * More formally, removes the first element {@code e} such that
318 : jsr166 1.29 * {@code Objects.equals(o, e)} (if such an element exists).
319 : jsr166 1.22 * Returns {@code true} if this deque contained the specified element
320 : jsr166 1.12 * (or equivalently, if this deque changed as a result of the call).
321 : dl 1.1 *
322 : dl 1.3 * @param o element to be removed from this deque, if present
323 : jsr166 1.22 * @return {@code true} if an element was removed as a result of this call
324 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
325 : jsr166 1.27 * is incompatible with this deque
326 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
327 :     * @throws NullPointerException if the specified element is null
328 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
329 : dl 1.1 */
330 : dl 1.3 boolean removeFirstOccurrence(Object o);
331 : dl 1.1
332 :     /**
333 : jsr166 1.8 * Removes the last occurrence of the specified element from this deque.
334 :     * If the deque does not contain the element, it is unchanged.
335 : jsr166 1.22 * More formally, removes the last element {@code e} such that
336 : jsr166 1.29 * {@code Objects.equals(o, e)} (if such an element exists).
337 : jsr166 1.22 * Returns {@code true} if this deque contained the specified element
338 : jsr166 1.12 * (or equivalently, if this deque changed as a result of the call).
339 : dl 1.1 *
340 : dl 1.3 * @param o element to be removed from this deque, if present
341 : jsr166 1.22 * @return {@code true} if an element was removed as a result of this call
342 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
343 : jsr166 1.27 * is incompatible with this deque
344 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
345 :     * @throws NullPointerException if the specified element is null
346 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
347 : dl 1.1 */
348 : dl 1.3 boolean removeLastOccurrence(Object o);
349 : dl 1.1
350 : jsr166 1.8 // *** Queue methods ***
351 : dl 1.1
352 : jsr166 1.8 /**
353 :     * Inserts the specified element into the queue represented by this deque
354 :     * (in other words, at the tail of this deque) if it is possible to do so
355 :     * immediately without violating capacity restrictions, returning
356 : jsr166 1.22 * {@code true} upon success and throwing an
357 :     * {@code IllegalStateException} if no space is currently available.
358 : jsr166 1.8 * When using a capacity-restricted deque, it is generally preferable to
359 :     * use {@link #offer(Object) offer}.
360 :     *
361 : jsr166 1.14 * <p>This method is equivalent to {@link #addLast}.
362 : jsr166 1.8 *
363 :     * @param e the element to add
364 : jsr166 1.22 * @return {@code true} (as specified by {@link Collection#add})
365 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
366 :     * time due to capacity restrictions
367 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
368 :     * prevents it from being added to this deque
369 : jsr166 1.8 * @throws NullPointerException if the specified element is null and this
370 :     * deque does not permit null elements
371 :     * @throws IllegalArgumentException if some property of the specified
372 :     * element prevents it from being added to this deque
373 :     */
374 :     boolean add(E e);
375 : dl 1.1
376 :     /**
377 :     * Inserts the specified element into the queue represented by this deque
378 : jsr166 1.8 * (in other words, at the tail of this deque) if it is possible to do so
379 :     * immediately without violating capacity restrictions, returning
380 : jsr166 1.22 * {@code true} upon success and {@code false} if no space is currently
381 : jsr166 1.8 * available. When using a capacity-restricted deque, this method is
382 :     * generally preferable to the {@link #add} method, which can fail to
383 :     * insert an element only by throwing an exception.
384 : dl 1.1 *
385 :     * <p>This method is equivalent to {@link #offerLast}.
386 :     *
387 : jsr166 1.8 * @param e the element to add
388 : jsr166 1.22 * @return {@code true} if the element was added to this deque, else
389 :     * {@code false}
390 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
391 :     * prevents it from being added to this deque
392 : dl 1.3 * @throws NullPointerException if the specified element is null and this
393 : jsr166 1.8 * deque does not permit null elements
394 :     * @throws IllegalArgumentException if some property of the specified
395 :     * element prevents it from being added to this deque
396 : dl 1.1 */
397 :     boolean offer(E e);
398 :    
399 :     /**
400 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
401 :     * (in other words, the first element of this deque).
402 : jsr166 1.15 * This method differs from {@link #poll poll} only in that it throws an
403 : jsr166 1.8 * exception if this deque is empty.
404 : dl 1.1 *
405 : jsr166 1.8 * <p>This method is equivalent to {@link #removeFirst()}.
406 : dl 1.1 *
407 : jsr166 1.8 * @return the head of the queue represented by this deque
408 :     * @throws NoSuchElementException if this deque is empty
409 : dl 1.1 */
410 : jsr166 1.8 E remove();
411 : dl 1.1
412 :     /**
413 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
414 :     * (in other words, the first element of this deque), or returns
415 : jsr166 1.22 * {@code null} if this deque is empty.
416 : dl 1.1 *
417 :     * <p>This method is equivalent to {@link #pollFirst()}.
418 :     *
419 : jsr166 1.22 * @return the first element of this deque, or {@code null} if
420 : jsr166 1.8 * this deque is empty
421 : dl 1.1 */
422 :     E poll();
423 :    
424 :     /**
425 : jsr166 1.8 * Retrieves, but does not remove, the head of the queue represented by
426 :     * this deque (in other words, the first element of this deque).
427 : jsr166 1.15 * This method differs from {@link #peek peek} only in that it throws an
428 : jsr166 1.8 * exception if this deque is empty.
429 : dl 1.1 *
430 : jsr166 1.8 * <p>This method is equivalent to {@link #getFirst()}.
431 : dl 1.1 *
432 :     * @return the head of the queue represented by this deque
433 :     * @throws NoSuchElementException if this deque is empty
434 :     */
435 : jsr166 1.8 E element();
436 : dl 1.1
437 :     /**
438 :     * Retrieves, but does not remove, the head of the queue represented by
439 : jsr166 1.8 * this deque (in other words, the first element of this deque), or
440 : jsr166 1.22 * returns {@code null} if this deque is empty.
441 : dl 1.1 *
442 : dl 1.3 * <p>This method is equivalent to {@link #peekFirst()}.
443 : dl 1.1 *
444 :     * @return the head of the queue represented by this deque, or
445 : jsr166 1.22 * {@code null} if this deque is empty
446 : dl 1.1 */
447 :     E peek();
448 :    
449 :    
450 :     // *** Stack methods ***
451 :    
452 :     /**
453 : jsr166 1.8 * Pushes an element onto the stack represented by this deque (in other
454 :     * words, at the head of this deque) if it is possible to do so
455 : jsr166 1.25 * immediately without violating capacity restrictions, throwing an
456 : jsr166 1.22 * {@code IllegalStateException} if no space is currently available.
457 : dl 1.1 *
458 :     * <p>This method is equivalent to {@link #addFirst}.
459 :     *
460 : dl 1.3 * @param e the element to push
461 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
462 :     * time due to capacity restrictions
463 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
464 :     * prevents it from being added to this deque
465 : dl 1.3 * @throws NullPointerException if the specified element is null and this
466 : jsr166 1.8 * deque does not permit null elements
467 :     * @throws IllegalArgumentException if some property of the specified
468 :     * element prevents it from being added to this deque
469 : dl 1.1 */
470 :     void push(E e);
471 :    
472 :     /**
473 :     * Pops an element from the stack represented by this deque. In other
474 : dl 1.2 * words, removes and returns the first element of this deque.
475 : dl 1.1 *
476 :     * <p>This method is equivalent to {@link #removeFirst()}.
477 :     *
478 :     * @return the element at the front of this deque (which is the top
479 : jsr166 1.8 * of the stack represented by this deque)
480 : dl 1.1 * @throws NoSuchElementException if this deque is empty
481 :     */
482 :     E pop();
483 :    
484 :    
485 : jsr166 1.8 // *** Collection methods ***
486 :    
487 :     /**
488 :     * Removes the first occurrence of the specified element from this deque.
489 :     * If the deque does not contain the element, it is unchanged.
490 : jsr166 1.22 * More formally, removes the first element {@code e} such that
491 : jsr166 1.29 * {@code Objects.equals(o, e)} (if such an element exists).
492 : jsr166 1.22 * Returns {@code true} if this deque contained the specified element
493 : jsr166 1.12 * (or equivalently, if this deque changed as a result of the call).
494 : jsr166 1.8 *
495 : jsr166 1.23 * <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
496 : jsr166 1.8 *
497 :     * @param o element to be removed from this deque, if present
498 : jsr166 1.22 * @return {@code true} if an element was removed as a result of this call
499 : jsr166 1.9 * @throws ClassCastException if the class of the specified element
500 : jsr166 1.27 * is incompatible with this deque
501 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
502 :     * @throws NullPointerException if the specified element is null
503 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
504 : jsr166 1.8 */
505 :     boolean remove(Object o);
506 :    
507 :     /**
508 : jsr166 1.22 * Returns {@code true} if this deque contains the specified element.
509 :     * More formally, returns {@code true} if and only if this deque contains
510 : jsr166 1.29 * at least one element {@code e} such that {@code Objects.equals(o, e)}.
511 : jsr166 1.8 *
512 :     * @param o element whose presence in this deque is to be tested
513 : jsr166 1.22 * @return {@code true} if this deque contains the specified element
514 : jsr166 1.27 * @throws ClassCastException if the class of the specified element
515 :     * is incompatible with this deque
516 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
517 :     * @throws NullPointerException if the specified element is null
518 :     * (<a href="../Collection.html#optional-restrictions">optional</a>)
519 : jsr166 1.8 */
520 :     boolean contains(Object o);
521 :    
522 :     /**
523 :     * Returns the number of elements in this deque.
524 :     *
525 :     * @return the number of elements in this deque
526 :     */
527 :     public int size();
528 : dl 1.1
529 :     /**
530 : jsr166 1.10 * Returns an iterator over the elements in this deque in proper sequence.
531 :     * The elements will be returned in order from first (head) to last (tail).
532 : dl 1.3 *
533 : jsr166 1.10 * @return an iterator over the elements in this deque in proper sequence
534 : dl 1.1 */
535 :     Iterator<E> iterator();
536 : dl 1.17
537 :     /**
538 :     * Returns an iterator over the elements in this deque in reverse
539 :     * sequential order. The elements will be returned in order from
540 :     * last (tail) to first (head).
541 :     *
542 :     * @return an iterator over the elements in this deque in reverse
543 :     * sequence
544 :     */
545 :     Iterator<E> descendingIterator();
546 :    
547 : dl 1.1 }

Doug Lea
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