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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 :     * at http://creativecommons.org/licenses/publicdomain
5 :     */
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 :     * and is usually pronounced "deck". Most <tt>Deque</tt>
13 :     * 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 :     * special value (either <tt>null</tt> or <tt>false</tt>, depending on
22 :     * the operation). The latter form of the insert operation is
23 :     * designed specifically for use with capacity-restricted
24 :     * <tt>Deque</tt> implementations; in most implementations, insert
25 :     * 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 * <p>
31 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
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 :     * <td>{@link #addFirst addFirst(e)}</td>
47 :     * <td>{@link #offerFirst offerFirst(e)}</td>
48 :     * <td>{@link #addLast addLast(e)}</td>
49 :     * <td>{@link #offerLast offerLast(e)}</td>
50 :     * </tr>
51 :     * <tr>
52 :     * <td><b>Remove</b></td>
53 :     * <td>{@link #removeFirst removeFirst()}</td>
54 :     * <td>{@link #pollFirst pollFirst()}</td>
55 :     * <td>{@link #removeLast removeLast()}</td>
56 :     * <td>{@link #pollLast pollLast()}</td>
57 :     * </tr>
58 :     * <tr>
59 :     * <td><b>Examine</b></td>
60 :     * <td>{@link #getFirst getFirst()}</td>
61 :     * <td>{@link #peekFirst peekFirst()}</td>
62 :     * <td>{@link #getLast getLast()}</td>
63 :     * <td>{@link #peekLast peekLast()}</td>
64 :     * </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 : dl 1.1 * inherited from the <tt>Queue</tt> interface are precisely equivalent to
71 : jsr166 1.5 * <tt>Deque</tt> methods as indicated in the following table:
72 : dl 1.1 *
73 : jsr166 1.7 * <p>
74 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
75 : dl 1.1 * <tr>
76 :     * <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
77 :     * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
78 :     * </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 1.5 * <tt>Deque</tt> methods as indicated in the table below:
110 : dl 1.1 *
111 : jsr166 1.7 * <p>
112 :     * <table BORDER CELLPADDING=3 CELLSPACING=1>
113 : dl 1.1 * <tr>
114 :     * <td ALIGN=CENTER> <b>Stack Method</b></td>
115 :     * <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
116 :     * </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 :     * <p>While <tt>Deque</tt> implementations are not strictly required
143 :     * to prohibit the insertion of null elements, they are strongly
144 :     * encouraged to do so. Users of any <tt>Deque</tt> implementations
145 :     * 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 :     * <tt>null</tt> is used as a special return value by various methods
148 :     * to indicated that the deque is empty.
149 : dl 1.3 *
150 : dl 1.1 * <p><tt>Deque</tt> implementations generally do not define
151 :     * element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
152 :     * methods, but instead inherit the identity-based versions from class
153 :     * <tt>Object</tt>.
154 :     *
155 :     * <p>This interface is a member of the <a
156 :     * href="{@docRoot}/../guide/collections/index.html"> Java Collections
157 :     * 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 :    
165 :     public interface Deque<E> extends Queue<E> {
166 :     /**
167 : jsr166 1.8 * Inserts the specified element at the front of this deque if it is
168 :     * possible to do so immediately without violating capacity restrictions.
169 :     * When using a capacity-restricted deque, it is generally preferable to
170 :     * use method {@link #offerFirst}.
171 :     *
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 :     * @throws NullPointerException if the specified element is null and this
176 :     * deque does not permit null elements
177 :     * @throws ClassCastException if the class of the specified element
178 :     * prevents it from being added to this deque
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 :     * Inserts the specified element at the end of this deque if it is
186 :     * possible to do so immediately without violating capacity restrictions.
187 :     * When using a capacity-restricted deque, it is generally preferable to
188 :     * use method {@link #offerLast}.
189 :     *
190 :     * @param e the element to add
191 :     * @throws IllegalStateException if the element cannot be added at this
192 :     * time due to capacity restrictions
193 :     * @throws NullPointerException if the specified element is null and this
194 :     * deque does not permit null elements
195 :     * @throws ClassCastException if the class of the specified element
196 :     * prevents it from being added to this deque
197 :     * @throws IllegalArgumentException if some property of the specified
198 :     * element prevents it from being added to this deque
199 :     */
200 :     void addLast(E e);
201 :    
202 :     /**
203 : dl 1.3 * Inserts the specified element at the front of this deque unless it would
204 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
205 : jsr166 1.8 * this method is generally preferable to the {@link #addFirst} method,
206 :     * which can fail to insert an element only by throwing an exception.
207 : dl 1.1 *
208 : jsr166 1.8 * @param e the element to add
209 : dl 1.1 * @return <tt>true</tt> if it was possible to insert the element,
210 : jsr166 1.8 * else <tt>false</tt>
211 : dl 1.3 * @throws NullPointerException if the specified element is null and this
212 : jsr166 1.8 * deque does not permit null elements
213 :     * @throws ClassCastException if the class of the specified element
214 :     * prevents it from being added to this deque
215 :     * @throws IllegalArgumentException if some property of the specified
216 :     * element prevents it from being added to this deque
217 : dl 1.1 */
218 :     boolean offerFirst(E e);
219 :    
220 :     /**
221 : dl 1.4 * Inserts the specified element at the end of this deque unless it would
222 : dl 1.1 * violate capacity restrictions. When using a capacity-restricted deque,
223 : jsr166 1.8 * this method is generally preferable to the {@link #addLast} method,
224 :     * which can fail to insert an element only by throwing an exception.
225 : dl 1.1 *
226 : jsr166 1.8 * @param e the element to add
227 : dl 1.1 * @return <tt>true</tt> if it was possible to insert the element,
228 : jsr166 1.8 * else <tt>false</tt>
229 : dl 1.3 * @throws NullPointerException if the specified element is null and this
230 : jsr166 1.8 * deque does not permit null elements
231 :     * @throws ClassCastException if the class of the specified element
232 :     * prevents it from being added to this deque
233 :     * @throws IllegalArgumentException if some property of the specified
234 :     * element prevents it from being added to this deque
235 : dl 1.1 */
236 :     boolean offerLast(E e);
237 :    
238 :     /**
239 : jsr166 1.8 * Retrieves and removes the first element of this deque. This method
240 :     * differs from {@link #pollFirst} only in that it throws an exception
241 :     * if this deque is empty.
242 : dl 1.1 *
243 : jsr166 1.8 * @return the head of this deque
244 :     * @throws NoSuchElementException if this deque is empty
245 : dl 1.1 */
246 : jsr166 1.8 E removeFirst();
247 : dl 1.1
248 :     /**
249 : jsr166 1.8 * Retrieves and removes the last element of this deque. This method
250 :     * differs from {@link #pollLast} only in that it throws an exception if
251 :     * this deque is empty.
252 : dl 1.1 *
253 : jsr166 1.8 * @return the tail of this deque
254 :     * @throws NoSuchElementException if this deque is empty
255 : dl 1.1 */
256 : jsr166 1.8 E removeLast();
257 : dl 1.1
258 :     /**
259 : jsr166 1.8 * Retrieves and removes the first element of this deque,
260 :     * or returns <tt>null</tt> if this deque is empty.
261 : dl 1.1 *
262 : jsr166 1.8 * @return the head of this deque, or <tt>null</tt> if this deque is empty
263 : dl 1.1 */
264 :     E pollFirst();
265 :    
266 :     /**
267 : jsr166 1.8 * Retrieves and removes the last element of this deque,
268 :     * or returns <tt>null</tt> if this deque is empty.
269 : dl 1.1 *
270 : jsr166 1.8 * @return the tail of this deque, or <tt>null</tt> if this deque is empty
271 : dl 1.1 */
272 :     E pollLast();
273 :    
274 :     /**
275 : jsr166 1.8 * Retrieves, but does not remove, the first element of this deque.
276 :     * This method differs from {@link #peekFirst} only in that it throws an
277 : dl 1.1 * exception if this deque is empty.
278 :     *
279 : jsr166 1.8 * @return the head of this deque
280 : dl 1.1 * @throws NoSuchElementException if this deque is empty
281 :     */
282 : jsr166 1.8 E getFirst();
283 : dl 1.1
284 :     /**
285 : jsr166 1.8 * Retrieves, but does not remove, the last element of this deque.
286 :     * This method differs from {@link #peekLast} only in that it throws an
287 : dl 1.1 * exception if this deque is empty.
288 :     *
289 : jsr166 1.8 * @return the tail of this deque
290 : dl 1.1 * @throws NoSuchElementException if this deque is empty
291 :     */
292 : jsr166 1.8 E getLast();
293 : dl 1.1
294 :     /**
295 :     * Retrieves, but does not remove, the first element of this deque,
296 : jsr166 1.8 * or returns <tt>null</tt> if this deque is empty.
297 : dl 1.1 *
298 : jsr166 1.8 * @return the head of this deque, or <tt>null</tt> if this deque is empty
299 : dl 1.1 */
300 :     E peekFirst();
301 :    
302 :     /**
303 :     * Retrieves, but does not remove, the last element of this deque,
304 : jsr166 1.8 * or returns <tt>null</tt> if this deque is empty.
305 : dl 1.1 *
306 : jsr166 1.8 * @return the tail of this deque, or <tt>null</tt> if this deque is empty
307 : dl 1.1 */
308 :     E peekLast();
309 :    
310 :     /**
311 : jsr166 1.8 * Removes the first occurrence of the specified element from this deque.
312 :     * If the deque does not contain the element, it is unchanged.
313 :     * More formally, removes the first element <tt>e</tt> such that
314 :     * <tt>(o==null ? e==null : o.equals(e))</tt> (if such an element exists).
315 :     * Returns true if this deque contained the specified element (or
316 :     * equivalently, if this deque changed as a result of the call).
317 : dl 1.1 *
318 : dl 1.3 * @param o element to be removed from this deque, if present
319 : jsr166 1.8 * @return <tt>true</tt> if an element was removed as a result of this call
320 : dl 1.4 * @throws NullPointerException if the specified element is null and this
321 : jsr166 1.8 * deque does not permit null elements (optional)
322 :     * @throws ClassCastException if the class of the specified element
323 :     * is incompatible with this collection (optional)
324 : dl 1.1 */
325 : dl 1.3 boolean removeFirstOccurrence(Object o);
326 : dl 1.1
327 :     /**
328 : jsr166 1.8 * Removes the last occurrence of the specified element from this deque.
329 :     * If the deque does not contain the element, it is unchanged.
330 :     * More formally, removes the last element <tt>e</tt> such that
331 :     * <tt>(o==null ? e==null : o.equals(e))</tt> (if such an element exists).
332 :     * Returns true if this deque contained the specified element (or
333 :     * equivalently, if this deque changed as a result of the call).
334 : dl 1.1 *
335 : dl 1.3 * @param o element to be removed from this deque, if present
336 : jsr166 1.8 * @return <tt>true</tt> if an element was removed as a result of this call
337 : dl 1.4 * @throws NullPointerException if the specified element is null and this
338 : jsr166 1.8 * deque does not permit null elements (optional)
339 :     * @throws ClassCastException if the class of the specified element
340 :     * is incompatible with this collection (optional)
341 : dl 1.1 */
342 : dl 1.3 boolean removeLastOccurrence(Object o);
343 : dl 1.1
344 : jsr166 1.8 // *** Queue methods ***
345 : dl 1.1
346 : jsr166 1.8 /**
347 :     * Inserts the specified element into the queue represented by this deque
348 :     * (in other words, at the tail of this deque) if it is possible to do so
349 :     * immediately without violating capacity restrictions, returning
350 :     * <tt>true</tt> upon success and throwing an
351 :     * <tt>IllegalStateException</tt> if no space is currently available.
352 :     * When using a capacity-restricted deque, it is generally preferable to
353 :     * use {@link #offer(Object) offer}.
354 :     *
355 :     * <p>This method is equivalent to {@link #addLast(Object) addLast}.
356 :     *
357 :     * @param e the element to add
358 :     * @return <tt>true</tt> (as per the spec for {@link Collection#add})
359 :     * @throws IllegalStateException if the element cannot be added at this
360 :     * time due to capacity restrictions
361 :     * @throws NullPointerException if the specified element is null and this
362 :     * deque does not permit null elements
363 :     * @throws ClassCastException if the class of the specified element
364 :     * prevents it from being added to this deque
365 :     * @throws IllegalArgumentException if some property of the specified
366 :     * element prevents it from being added to this deque
367 :     */
368 :     boolean add(E e);
369 : dl 1.1
370 :     /**
371 :     * Inserts the specified element into the queue represented by this deque
372 : jsr166 1.8 * (in other words, at the tail of this deque) if it is possible to do so
373 :     * immediately without violating capacity restrictions, returning
374 :     * <tt>true</tt> upon success and <tt>false</tt> if no space is currently
375 :     * available. When using a capacity-restricted deque, this method is
376 :     * generally preferable to the {@link #add} method, which can fail to
377 :     * insert an element only by throwing an exception.
378 : dl 1.1 *
379 :     * <p>This method is equivalent to {@link #offerLast}.
380 :     *
381 : jsr166 1.8 * @param e the element to add
382 :     * @return <tt>true</tt> if the element was added to this deque, else
383 :     * <tt>false</tt>
384 : dl 1.3 * @throws NullPointerException if the specified element is null and this
385 : jsr166 1.8 * deque does not permit null elements
386 :     * @throws ClassCastException if the class of the specified element
387 :     * prevents it from being added to this deque
388 :     * @throws IllegalArgumentException if some property of the specified
389 :     * element prevents it from being added to this deque
390 : dl 1.1 */
391 :     boolean offer(E e);
392 :    
393 :     /**
394 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
395 :     * (in other words, the first element of this deque).
396 :     * This method differs from {@link #poll} only in that it throws an
397 :     * exception if this deque is empty.
398 : dl 1.1 *
399 : jsr166 1.8 * <p>This method is equivalent to {@link #removeFirst()}.
400 : dl 1.1 *
401 : jsr166 1.8 * @return the head of the queue represented by this deque
402 :     * @throws NoSuchElementException if this deque is empty
403 : dl 1.1 */
404 : jsr166 1.8 E remove();
405 : dl 1.1
406 :     /**
407 : jsr166 1.8 * Retrieves and removes the head of the queue represented by this deque
408 :     * (in other words, the first element of this deque), or returns
409 :     * <tt>null</tt> if this deque is empty.
410 : dl 1.1 *
411 :     * <p>This method is equivalent to {@link #pollFirst()}.
412 :     *
413 :     * @return the first element of this deque, or <tt>null</tt> if
414 : jsr166 1.8 * this deque is empty
415 : dl 1.1 */
416 :     E poll();
417 :    
418 :     /**
419 : jsr166 1.8 * Retrieves, but does not remove, the head of the queue represented by
420 :     * this deque (in other words, the first element of this deque).
421 :     * This method differs from {@link #peek} only in that it throws an
422 :     * exception if this deque is empty.
423 : dl 1.1 *
424 : jsr166 1.8 * <p>This method is equivalent to {@link #getFirst()}.
425 : dl 1.1 *
426 :     * @return the head of the queue represented by this deque
427 :     * @throws NoSuchElementException if this deque is empty
428 :     */
429 : jsr166 1.8 E element();
430 : dl 1.1
431 :     /**
432 :     * Retrieves, but does not remove, the head of the queue represented by
433 : jsr166 1.8 * this deque (in other words, the first element of this deque), or
434 :     * returns <tt>null</tt> if this deque is empty.
435 : dl 1.1 *
436 : dl 1.3 * <p>This method is equivalent to {@link #peekFirst()}.
437 : dl 1.1 *
438 :     * @return the head of the queue represented by this deque, or
439 : jsr166 1.8 * <tt>null</tt> if this deque is empty
440 : dl 1.1 */
441 :     E peek();
442 :    
443 :    
444 :     // *** Stack methods ***
445 :    
446 :     /**
447 : jsr166 1.8 * Pushes an element onto the stack represented by this deque (in other
448 :     * words, at the head of this deque) if it is possible to do so
449 :     * immediately without violating capacity restrictions, returning
450 :     * <tt>true</tt> upon success and throwing an
451 :     * <tt>IllegalStateException</tt> if no space is currently available.
452 : dl 1.1 *
453 :     * <p>This method is equivalent to {@link #addFirst}.
454 :     *
455 : dl 1.3 * @param e the element to push
456 : jsr166 1.8 * @throws IllegalStateException if the element cannot be added at this
457 :     * time due to capacity restrictions
458 : dl 1.3 * @throws NullPointerException if the specified element is null and this
459 : jsr166 1.8 * deque does not permit null elements
460 :     * @throws ClassCastException if the class of the specified element
461 :     * prevents it from being added to this deque
462 :     * @throws IllegalArgumentException if some property of the specified
463 :     * element prevents it from being added to this deque
464 : dl 1.1 */
465 :     void push(E e);
466 :    
467 :     /**
468 :     * Pops an element from the stack represented by this deque. In other
469 : dl 1.2 * words, removes and returns the first element of this deque.
470 : dl 1.1 *
471 :     * <p>This method is equivalent to {@link #removeFirst()}.
472 :     *
473 :     * @return the element at the front of this deque (which is the top
474 : jsr166 1.8 * of the stack represented by this deque)
475 : dl 1.1 * @throws NoSuchElementException if this deque is empty
476 :     */
477 :     E pop();
478 :    
479 :    
480 : jsr166 1.8 // *** Collection methods ***
481 :    
482 :     /**
483 :     * Removes the first occurrence of the specified element from this deque.
484 :     * If the deque does not contain the element, it is unchanged.
485 :     * More formally, removes the first element <tt>e</tt> such that
486 :     * <tt>(o==null ? e==null : o.equals(e))</tt> (if such an element exists).
487 :     * Returns true if this deque contained the specified element (or
488 :     * equivalently, if this deque changed as a result of the call).
489 :     *
490 :     * <p>This method is equivalent to {@link #removeFirstOccurrence}.
491 :     *
492 :     * @param o element to be removed from this deque, if present
493 :     * @return <tt>true</tt> if an element was removed as a result of this call
494 :     * @throws NullPointerException if the specified element is null and this
495 :     * deque does not permit null elements (optional)
496 :     * @throws ClassCastException if the class of the specified element
497 :     * is incompatible with this collection (optional)
498 :     */
499 :     boolean remove(Object o);
500 :    
501 :     /**
502 :     * Returns <tt>true</tt> if this deque contains the specified element.
503 :     * More formally, returns <tt>true</tt> if and only if this deque
504 :     * contains at least one element <tt>e</tt> such that <tt>(o==null ?
505 :     * e==null : o.equals(e))</tt>.
506 :     *
507 :     * @param o element whose presence in this deque is to be tested
508 :     * @return <tt>true</tt> if this deque contains the specified element
509 :     * @throws ClassCastException if the type of the specified element
510 :     * is incompatible with this deque (optional)
511 :     * @throws NullPointerException if the specified element is null and this
512 :     * deque does not permit null elements (optional)
513 :     */
514 :     boolean contains(Object o);
515 :    
516 :     /**
517 :     * Returns the number of elements in this deque.
518 :     *
519 :     * @return the number of elements in this deque
520 :     */
521 :     public int size();
522 : dl 1.1
523 :     /**
524 :     * Returns an iterator over the elements in this deque. The elements
525 :     * will be ordered from first (head) to last (tail).
526 : dl 1.3 *
527 : dl 1.1 * @return an <tt>Iterator</tt> over the elements in this deque
528 :     */
529 :     Iterator<E> iterator();
530 :     }

Doug Lea
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