1 |
|
/* |
2 |
< |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
< |
* Expert Group and released to the public domain, as explained at |
4 |
< |
* http://creativecommons.org/licenses/publicdomain |
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 jsr166x; |
8 |
< |
import java.util.*; |
7 |
> |
package jsr166x; // XXX This belongs in java.util!!! XXX |
8 |
> |
import java.util.*; // XXX This import goes away XXX |
9 |
|
|
10 |
|
/** |
11 |
< |
* A linear collection in which elements may be inserted and removed |
12 |
< |
* from both the beginning and end. A <tt>Deque</tt> (short for |
13 |
< |
* "double ended queue") provides uniformly named methods to |
14 |
< |
* <tt>get</tt>, <tt>peek</tt>, <tt>poll</tt>, <tt>remove</tt>, |
15 |
< |
* <tt>offer</tt>, and <tt>add</tt> the <tt>first</tt> and |
16 |
< |
* <tt>last</tt> element of the collection (for example, methods |
17 |
< |
* <tt>addFirst</tt>, <tt>pollLast</tt>). Unlike interface {@link |
18 |
< |
* List} the Deque interface does not define support for indexed |
19 |
< |
* operations or sublists. |
20 |
< |
* |
21 |
< |
* <p>A view of a subset of Deque operations can be obtained using |
22 |
< |
* method {@link #asFifoQueue} to support only Last-In-First-Out (LIFO) |
23 |
< |
* stack behavior, as well as method {@link #asFifoQueue} to support only |
24 |
< |
* First-in-First-Out (FIFO) queue behavior. More commonly, a Deque |
25 |
< |
* is used when various mixtures of LIFO and FIFO operations are |
26 |
< |
* required. |
27 |
< |
* |
28 |
< |
* <p>Deques additionally provide a few methods to remove elements |
29 |
< |
* embedded within a deque, proceding from either direction using |
30 |
< |
* <tt>removeFirstOccurrence</tt> and <tt>removeLastOccurrence</tt>. |
31 |
< |
* They also support {@link Collection} operations including |
32 |
< |
* <tt>contains</tt>, <tt>iterator</tt>, and so on. |
33 |
< |
* |
34 |
< |
* <p>The {@link #offerFirst} and {@link #offerLast} methods insert an |
35 |
< |
* element if possible, otherwise returning <tt>false</tt>. They |
36 |
< |
* differ from {@link java.util.Collection#add Collection.add}, as |
37 |
< |
* well as {@link #addFirst} and {@link #addLast} methods, which can |
38 |
< |
* fail to add an element only by throwing an unchecked exception. |
39 |
< |
* The <tt>offer</tt> methods are designed for use when failure is a |
40 |
< |
* normal, rather than exceptional occurrence, for example, in |
41 |
< |
* fixed-capacity (or "bounded") deques. |
42 |
< |
* |
43 |
< |
* <p><tt>Deque</tt> implementations generally do not allow insertion |
44 |
< |
* of <tt>null</tt> elements. Even in implementations that permit it, |
45 |
< |
* <tt>null</tt> should not be inserted into a <tt>Deque</tt>, as |
46 |
< |
* <tt>null</tt> is also used as a special return value by the poll |
47 |
< |
* methods to indicate that the deque contains no elements. |
11 |
> |
* A linear collection that supports element insertion and removal at |
12 |
> |
* both ends. The name <i>deque</i> is short for "double ended queue" |
13 |
> |
* and is usually pronounced "deck". Most <tt>Deque</tt> |
14 |
> |
* implementations place no fixed limits on the number of elements |
15 |
> |
* they may contain, but this interface supports capacity-restricted |
16 |
> |
* deques as well as those with no fixed size limit. |
17 |
> |
* |
18 |
> |
* <p>This interface defines methods to access the elements at both |
19 |
> |
* ends of the deque. Methods are provided to insert, remove, and |
20 |
> |
* examine the element. Each of these methods exists in two forms: |
21 |
> |
* one throws an exception if the operation fails, the other returns a |
22 |
> |
* special value (either <tt>null</tt> or <tt>false</tt>, depending on |
23 |
> |
* the operation). The latter form of the insert operation is |
24 |
> |
* designed specifically for use with capacity-restricted |
25 |
> |
* <tt>Deque</tt> implementations; in most implementations, insert |
26 |
> |
* operations cannot fail. |
27 |
> |
* |
28 |
> |
* <p>The twelve methods described above are are summarized in the |
29 |
> |
* follwoing table:<p> |
30 |
> |
* |
31 |
> |
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
32 |
> |
* <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 |
> |
* <td ALIGN=CENTER><em>Returns special value</em></td> |
41 |
> |
* <td ALIGN=CENTER><em>Throws exception</em></td> |
42 |
> |
* <td ALIGN=CENTER><em>Returns special value</em></td> |
43 |
> |
* </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 |
> |
* added to the end of the deque and removed from the beginning. The methods |
70 |
> |
* inherited from the <tt>Queue</tt> interface are precisely equivalent to |
71 |
> |
* <tt>Deque</tt> methods as indicated in the following table:<p> |
72 |
> |
* |
73 |
> |
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
74 |
> |
* <tr> |
75 |
> |
* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td> |
76 |
> |
* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> |
77 |
> |
* </tr> |
78 |
> |
* <tr> |
79 |
> |
* <tr> |
80 |
> |
* <td>{@link java.util.Queue#offer offer(e)}</td> |
81 |
> |
* <td>{@link #offerLast offerLast(e)}</td> |
82 |
> |
* </tr> |
83 |
> |
* <tr> |
84 |
> |
* <td>{@link java.util.Queue#add add(e)}</td> |
85 |
> |
* <td>{@link #addLast addLast(e)}</td> |
86 |
> |
* </tr> |
87 |
> |
* <tr> |
88 |
> |
* <td>{@link java.util.Queue#poll poll()}</td> |
89 |
> |
* <td>{@link #pollFirst pollFirst()}</td> |
90 |
> |
* </tr> |
91 |
> |
* <tr> |
92 |
> |
* <td>{@link java.util.Queue#remove remove()}</td> |
93 |
> |
* <td>{@link #removeFirst removeFirst()}</td> |
94 |
> |
* </tr> |
95 |
> |
* <tr> |
96 |
> |
* <td>{@link java.util.Queue#peek peek()}</td> |
97 |
> |
* <td>{@link #peek peekFirst()}</td> |
98 |
> |
* </tr> |
99 |
> |
* <tr> |
100 |
> |
* <td>{@link java.util.Queue#element element()}</td> |
101 |
> |
* <td>{@link #getFirst getFirst()}</td> |
102 |
> |
* </tr> |
103 |
> |
* </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 |
> |
* When a dequeue is used as a stack, elements are pushed and popped from the |
108 |
> |
* beginning of the deque. Stack methods are precisely equivalent to |
109 |
> |
* <tt>Deque</tt> methods as indicated in the table below:<p> |
110 |
> |
* |
111 |
> |
* <table BORDER CELLPADDING=3 CELLSPACING=1> |
112 |
> |
* <tr> |
113 |
> |
* <td ALIGN=CENTER> <b>Stack Method</b></td> |
114 |
> |
* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> |
115 |
> |
* </tr> |
116 |
> |
* <tr> |
117 |
> |
* <tr> |
118 |
> |
* <td>{@link #push push(e)}</td> |
119 |
> |
* <td>{@link #addFirst addFirst(e)}</td> |
120 |
> |
* </tr> |
121 |
> |
* <tr> |
122 |
> |
* <td>{@link #pop pop()}</td> |
123 |
> |
* <td>{@link #removeFirst removeFirst()}</td> |
124 |
> |
* </tr> |
125 |
> |
* <tr> |
126 |
> |
* <td>{@link #peek peek()}</td> |
127 |
> |
* <td>{@link #peekFirst peekFirst()}</td> |
128 |
> |
* </tr> |
129 |
> |
* </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 |
> |
* <p>This inteface provides two methods to to remove interior |
136 |
> |
* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and |
137 |
> |
* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the |
138 |
> |
* {@link List} interface, this interface does not provide support for |
139 |
> |
* indexed access to elements. |
140 |
> |
* |
141 |
> |
* <p>While <tt>Deque</tt> implementations are not strictly required |
142 |
> |
* to prohibit the insertion of null elements, they are strongly |
143 |
> |
* encouraged to do so. Users of any <tt>Deque</tt> implementations |
144 |
> |
* that do allow null elements are strongly encouraged <i>not</i> to |
145 |
> |
* take advantage of the ability to insert nulls. This is so because |
146 |
> |
* <tt>null</tt> is used as a special return value by various methods |
147 |
> |
* to indicated that the deque is empty. |
148 |
|
* |
149 |
|
* <p><tt>Deque</tt> implementations generally do not define |
150 |
< |
* element-based versions of methods <tt>equals</tt> and |
151 |
< |
* <tt>hashCode</tt> but instead inherit the identity based versions |
152 |
< |
* from class <tt>Object</tt>. |
150 |
> |
* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt> |
151 |
> |
* methods, but instead inherit the identity-based versions from class |
152 |
> |
* <tt>Object</tt>. |
153 |
|
* |
154 |
|
* <p>This interface is a member of the <a |
155 |
|
* href="{@docRoot}/../guide/collections/index.html"> Java Collections |
156 |
|
* Framework</a>. |
157 |
|
* |
158 |
|
* @author Doug Lea |
159 |
+ |
* @author Josh Bloch |
160 |
+ |
* @since 1.6 |
161 |
|
* @param <E> the type of elements held in this collection |
162 |
|
*/ |
163 |
< |
public interface Deque<E> extends Collection<E> { |
62 |
< |
|
163 |
> |
public interface Deque<E> extends Queue<E> { |
164 |
|
/** |
165 |
< |
* Inserts the specified element to the front this deque, if |
166 |
< |
* possible. When using deques that may impose insertion |
167 |
< |
* restrictions (for example capacity bounds), method |
168 |
< |
* <tt>offerFirst</tt> is generally preferable to method |
68 |
< |
* <tt>addFirst</tt> which can fail to insert a non-duplicate |
69 |
< |
* element only by throwing an exception. |
165 |
> |
* Inserts the specified element to the front this deque unless it would |
166 |
> |
* violate capacity restrictions. When using a capacity-restricted deque, |
167 |
> |
* this method is generally preferable to method <tt>addFirst</tt>, which |
168 |
> |
* can fail to insert an element only by throwing an exception. |
169 |
|
* |
170 |
< |
* @param o the element to insert. |
171 |
< |
* @return <tt>true</tt> if it was possible to add the element to |
172 |
< |
* this deque, else <tt>false</tt> |
170 |
> |
* @param e the element to insert |
171 |
> |
* @return <tt>true</tt> if it was possible to insert the element, |
172 |
> |
* else <tt>false</tt> |
173 |
> |
* @throws NullPointerException if <tt>e</tt> is null and this |
174 |
> |
* deque does not permit null elements |
175 |
|
*/ |
176 |
< |
boolean offerFirst(E o); |
176 |
> |
boolean offerFirst(E e); |
177 |
|
|
178 |
|
/** |
179 |
< |
* Inserts the specified element to the end this deque, if |
180 |
< |
* possible. When using deques that may impose insertion |
181 |
< |
* restrictions (for example capacity bounds), method |
182 |
< |
* <tt>offerFirst</tt> is generally preferable to method |
82 |
< |
* <tt>addLast</tt> which can fail to insert a non-duplicate |
83 |
< |
* element only by throwing an exception. |
179 |
> |
* Inserts the specified element to the end of this deque unless it would |
180 |
> |
* violate capacity restrictions. When using a capacity-restricted deque, |
181 |
> |
* this method is generally preferable to method <tt>addLast</tt> which |
182 |
> |
* can fail to insert an element only by throwing an exception. |
183 |
|
* |
184 |
< |
* @param o the element to insert. |
185 |
< |
* @return <tt>true</tt> if it was possible to add the element to |
186 |
< |
* this deque, else <tt>false</tt> |
184 |
> |
* @param e the element to insert |
185 |
> |
* @return <tt>true</tt> if it was possible to insert the element, |
186 |
> |
* else <tt>false</tt> |
187 |
> |
* @throws NullPointerException if <tt>e</tt> is null and this |
188 |
> |
* deque does not permit null elements |
189 |
|
*/ |
190 |
< |
boolean offerLast(E o); |
190 |
> |
boolean offerLast(E e); |
191 |
|
|
192 |
|
/** |
193 |
< |
* Inserts the specified element to the front this deque, if |
194 |
< |
* this deque permits insertion of the given element. This |
94 |
< |
* method has the same semantics as {@link Collection#add}. |
193 |
> |
* Inserts the specified element to the front of this deque unless it |
194 |
> |
* would violate capacity restrictions. |
195 |
|
* |
196 |
< |
* @param o the element to insert. |
197 |
< |
* @return <tt>true</tt> if this deque changed as a result of this |
198 |
< |
* call, else <tt>false</tt> |
196 |
> |
* @param e the element to insert |
197 |
> |
* @throws IllegalStateException if it was not possible to insert |
198 |
> |
* the element due to capacity restrictions |
199 |
> |
* @throws NullPointerException if <tt>e</tt> is null and this |
200 |
> |
* deque does not permit null elements |
201 |
|
*/ |
202 |
< |
boolean addFirst(E o); |
202 |
> |
void addFirst(E e); |
203 |
|
|
204 |
|
/** |
205 |
< |
* Inserts the specified element to the end this deque, if |
206 |
< |
* this deque permits insertion of the given element. This |
105 |
< |
* method has the same semantics as {@link Collection#add}. |
205 |
> |
* Inserts the specified element to the end of this deque unless it would |
206 |
> |
* violate capacity restrictions. |
207 |
|
* |
208 |
< |
* @param o the element to insert. |
209 |
< |
* @return <tt>true</tt> if this deque changed as a result of this |
210 |
< |
* call, else <tt>false</tt> |
208 |
> |
* @param e the element to insert |
209 |
> |
* @throws IllegalStateException if it was not possible to insert |
210 |
> |
* the element due to capacity restrictions |
211 |
> |
* @throws NullPointerException if <tt>e</tt> is null and this |
212 |
> |
* deque does not permit null elements |
213 |
|
*/ |
214 |
< |
boolean addLast(E o); |
214 |
> |
void addLast(E e); |
215 |
|
|
216 |
|
/** |
217 |
|
* Retrieves and removes the first element of this deque, or |
218 |
|
* <tt>null</tt> if this deque is empty. |
219 |
|
* |
220 |
|
* @return the first element of this deque, or <tt>null</tt> if |
221 |
< |
* this deque is empty. |
221 |
> |
* this deque is empty |
222 |
|
*/ |
223 |
|
E pollFirst(); |
224 |
|
|
227 |
|
* <tt>null</tt> if this deque is empty. |
228 |
|
* |
229 |
|
* @return the last element of this deque, or <tt>null</tt> if |
230 |
< |
* this deque is empty. |
230 |
> |
* this deque is empty |
231 |
|
*/ |
232 |
|
E pollLast(); |
233 |
|
|
234 |
|
/** |
235 |
< |
* Retrieves and removes the first element of this deque. This method |
236 |
< |
* differs from the <tt>pollFirst</tt> method in that it throws an |
235 |
> |
* Removes and returns the first element of this deque. This method |
236 |
> |
* differs from the <tt>pollFirst</tt> method only in that it throws an |
237 |
|
* exception if this deque is empty. |
238 |
|
* |
239 |
< |
* @return the first element of this deque. |
240 |
< |
* @throws NoSuchElementException if this deque is empty. |
239 |
> |
* @return the first element of this deque |
240 |
> |
* @throws NoSuchElementException if this deque is empty |
241 |
|
*/ |
242 |
|
E removeFirst(); |
243 |
|
|
244 |
|
/** |
245 |
|
* Retrieves and removes the last element of this deque. This method |
246 |
< |
* differs from the <tt>pollLast</tt> method in that it throws an |
246 |
> |
* differs from the <tt>pollLast</tt> method only in that it throws an |
247 |
|
* exception if this deque is empty. |
248 |
|
* |
249 |
< |
* @return the last element of this deque. |
250 |
< |
* @throws NoSuchElementException if this deque is empty. |
249 |
> |
* @return the last element of this deque |
250 |
> |
* @throws NoSuchElementException if this deque is empty |
251 |
|
*/ |
252 |
|
E removeLast(); |
253 |
|
|
256 |
|
* returning <tt>null</tt> if this deque is empty. |
257 |
|
* |
258 |
|
* @return the first element of this deque, or <tt>null</tt> if |
259 |
< |
* this deque is empty. |
259 |
> |
* this deque is empty |
260 |
|
*/ |
261 |
|
E peekFirst(); |
262 |
|
|
265 |
|
* returning <tt>null</tt> if this deque is empty. |
266 |
|
* |
267 |
|
* @return the last element of this deque, or <tt>null</tt> if this deque |
268 |
< |
* is empty. |
268 |
> |
* is empty |
269 |
|
*/ |
270 |
|
E peekLast(); |
271 |
|
|
274 |
|
* deque. This method differs from the <tt>peek</tt> method only |
275 |
|
* in that it throws an exception if this deque is empty. |
276 |
|
* |
277 |
< |
* @return the first element of this deque. |
278 |
< |
* @throws NoSuchElementException if this deque is empty. |
277 |
> |
* @return the first element of this deque |
278 |
> |
* @throws NoSuchElementException if this deque is empty |
279 |
|
*/ |
280 |
|
E getFirst(); |
281 |
|
|
284 |
|
* deque. This method differs from the <tt>peek</tt> method only |
285 |
|
* in that it throws an exception if this deque is empty. |
286 |
|
* |
287 |
< |
* @return the last element of this deque. |
288 |
< |
* @throws NoSuchElementException if this deque is empty. |
287 |
> |
* @return the last element of this deque |
288 |
> |
* @throws NoSuchElementException if this deque is empty |
289 |
|
*/ |
290 |
|
E getLast(); |
291 |
|
|
296 |
|
* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if |
297 |
|
* such an element exists). |
298 |
|
* |
299 |
< |
* @param o element to be removed from this deque, if present. |
300 |
< |
* @return <tt>true</tt> if the deque contained the specified element. |
299 |
> |
* @param e element to be removed from this deque, if present |
300 |
> |
* @return <tt>true</tt> if the deque contained the specified element |
301 |
|
* @throws NullPointerException if the specified element is <tt>null</tt> |
302 |
|
*/ |
303 |
< |
boolean removeFirstOccurrence(E o); |
303 |
> |
boolean removeFirstOccurrence(Object e); |
304 |
|
|
305 |
|
/** |
306 |
|
* Removes the last occurrence of the specified element in this |
309 |
|
* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if |
310 |
|
* such an element exists). |
311 |
|
* |
312 |
< |
* @param o element to be removed from this deque, if present. |
313 |
< |
* @return <tt>true</tt> if the deque contained the specified element. |
312 |
> |
* @param e element to be removed from this deque, if present |
313 |
> |
* @return <tt>true</tt> if the deque contained the specified element |
314 |
|
* @throws NullPointerException if the specified element is <tt>null</tt> |
315 |
|
*/ |
316 |
< |
boolean removeLastOccurrence(E o); |
316 |
> |
boolean removeLastOccurrence(Object e); |
317 |
> |
|
318 |
> |
|
319 |
> |
// *** Queue methods *** |
320 |
> |
|
321 |
> |
/** |
322 |
> |
* Inserts the specified element into the queue represented by this deque |
323 |
> |
* unless it would violate capacity restrictions. In other words, inserts |
324 |
> |
* the specified element to the end of this deque. When using a |
325 |
> |
* capacity-restricted deque, this method is generally preferable to the |
326 |
> |
* {@link #add} method, which can fail to insert an element only by |
327 |
> |
* throwing an exception. |
328 |
> |
* |
329 |
> |
* <p>This method is equivalent to {@link #offerLast}. |
330 |
> |
* |
331 |
> |
* @param e the element to insert |
332 |
> |
* @return <tt>true</tt> if it was possible to insert the element, |
333 |
> |
* else <tt>false</tt> |
334 |
> |
* @throws NullPointerException if <tt>e</tt> is null and this |
335 |
> |
* deque does not permit null elements |
336 |
> |
*/ |
337 |
> |
boolean offer(E e); |
338 |
> |
|
339 |
> |
/** |
340 |
> |
* Inserts the specified element into the queue represented by this |
341 |
> |
* deque unless it would violate capacity restrictions. In other words, |
342 |
> |
* inserts the specified element as the last element of this deque. |
343 |
> |
* |
344 |
> |
* <p>This method is equivalent to {@link #addLast}. |
345 |
> |
* |
346 |
> |
* @param e the element to insert |
347 |
> |
* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
348 |
> |
* @throws IllegalStateException if it was not possible to insert |
349 |
> |
* the element due to capacity restrictions |
350 |
> |
* @throws NullPointerException if <tt>e</tt> is null and this |
351 |
> |
* deque does not permit null elements |
352 |
> |
*/ |
353 |
> |
boolean add(E e); |
354 |
> |
|
355 |
> |
/** |
356 |
> |
* Retrieves and removes the head of the queue represented by |
357 |
> |
* this deque, or <tt>null</tt> if this deque is empty. In other words, |
358 |
> |
* retrieves and removes the first element of this deque, or <tt>null</tt> |
359 |
> |
* if this deque is empty. |
360 |
> |
* |
361 |
> |
* <p>This method is equivalent to {@link #pollFirst()}. |
362 |
> |
* |
363 |
> |
* @return the first element of this deque, or <tt>null</tt> if |
364 |
> |
* this deque is empty |
365 |
> |
*/ |
366 |
> |
E poll(); |
367 |
> |
|
368 |
> |
/** |
369 |
> |
* Retrieves and removes the head of the queue represented by this deque. |
370 |
> |
* This method differs from the <tt>poll</tt> method only in that it |
371 |
> |
* throws an exception if this deque is empty. |
372 |
> |
* |
373 |
> |
* <p>This method is equivalent to {@link #removeFirst()}. |
374 |
> |
* |
375 |
> |
* @return the head of the queue represented by this deque |
376 |
> |
* @throws NoSuchElementException if this deque is empty |
377 |
> |
*/ |
378 |
> |
E remove(); |
379 |
|
|
380 |
|
/** |
381 |
< |
* Returns a view of this deque as a first-in-first-out queue, |
382 |
< |
* mapping {@link Queue#offer} to <tt>offerLast</tt>, {@link |
383 |
< |
* Queue#poll} to <tt>pollFirst</tt>, and other operations |
384 |
< |
* accordingly. |
385 |
< |
* @return a first-in-first-out view of this deque. |
381 |
> |
* Retrieves, but does not remove, the head of the queue represented by |
382 |
> |
* this deque, returning <tt>null</tt> if this deque is empty. |
383 |
> |
* |
384 |
> |
* <p>This method is equivalent to {@link #peekFirst()} |
385 |
> |
* |
386 |
> |
* @return the head of the queue represented by this deque, or |
387 |
> |
* <tt>null</tt> if this deque is empty |
388 |
|
*/ |
389 |
< |
public Queue<E> asFifoQueue(); |
389 |
> |
E peek(); |
390 |
|
|
391 |
|
/** |
392 |
< |
* Returns a view of this deque as a last-in-first-out stack, |
393 |
< |
* mapping {@link Queue#offer} to <tt>offerFirst</tt>, {@link |
394 |
< |
* Queue#poll} to <tt>pollFirst</tt>, and other operations |
395 |
< |
* accordingly. |
396 |
< |
* @return a first-in-last-out view of this deque. |
392 |
> |
* Retrieves, but does not remove, the head of the queue represented by |
393 |
> |
* this deque. This method differs from the <tt>peek</tt> method only in |
394 |
> |
* that it throws an exception if this deque is empty. |
395 |
> |
* |
396 |
> |
* <p>This method is equivalent to {@link #getFirst()} |
397 |
> |
* |
398 |
> |
* @return the head of the queue represented by this deque |
399 |
> |
* @throws NoSuchElementException if this deque is empty |
400 |
|
*/ |
401 |
< |
public Queue<E> asLifoQueue(); |
401 |
> |
E element(); |
402 |
|
|
403 |
+ |
|
404 |
+ |
// *** Stack methods *** |
405 |
+ |
|
406 |
+ |
/** |
407 |
+ |
* Pushes an element onto the stack represented by this deque. In other |
408 |
+ |
* words, inserts the element to the front this deque unless it would |
409 |
+ |
* violate capacity restrictions. |
410 |
+ |
* |
411 |
+ |
* <p>This method is equivalent to {@link #addFirst}. |
412 |
+ |
* |
413 |
+ |
* @throws IllegalStateException if it was not possible to insert |
414 |
+ |
* the element due to capacity restrictions |
415 |
+ |
* @throws NullPointerException if <tt>e</tt> is null and this |
416 |
+ |
* deque does not permit null elements |
417 |
+ |
*/ |
418 |
+ |
void push(E e); |
419 |
+ |
|
420 |
+ |
/** |
421 |
+ |
* Pops an element from the stack represented by this deque. In other |
422 |
+ |
* words, removes and returns the the first element of this deque. |
423 |
+ |
* |
424 |
+ |
* <p>This method is equivalent to {@link #removeFirst()}. |
425 |
+ |
* |
426 |
+ |
* @return the element at the front of this deque (which is the top |
427 |
+ |
* of the stack represented by this deque) |
428 |
+ |
* @throws NoSuchElementException if this deque is empty |
429 |
+ |
*/ |
430 |
+ |
E pop(); |
431 |
+ |
|
432 |
+ |
|
433 |
+ |
// *** Collection Method *** |
434 |
+ |
|
435 |
+ |
/** |
436 |
+ |
* Returns an iterator over the elements in this deque. The elements |
437 |
+ |
* will be ordered from first (head) to last (tail). |
438 |
+ |
* |
439 |
+ |
* @return an <tt>Iterator</tt> over the elements in this deque |
440 |
+ |
*/ |
441 |
+ |
Iterator<E> iterator(); |
442 |
|
} |