src/jsr166x/Deque.java

/*
 * Written by Doug Lea and Josh Bloch with assistance from members of
 * JCP JSR-166 Expert Group and released to the public domain, as explained
 * at http://creativecommons.org/publicdomain/zero/1.0/
 */

package jsr166x;     // XXX This belongs in java.util!!! XXX

import java.util.*;    // XXX This import goes away        XXX

/**
 * A linear collection that supports element insertion and removal at
 * both ends.  The name <i>deque</i> is short for "double ended queue"
 * and is usually pronounced "deck".  Most {@code Deque}
 * implementations place no fixed limits on the number of elements
 * they may contain, but this interface supports capacity-restricted
 * deques as well as those with no fixed size limit.
 *
 * <p>This interface defines methods to access the elements at both
 * ends of the deque.  Methods are provided to insert, remove, and
 * examine the element.  Each of these methods exists in two forms:
 * one throws an exception if the operation fails, the other returns a
 * special value (either {@code null} or {@code false}, depending on
 * the operation).  The latter form of the insert operation is
 * designed specifically for use with capacity-restricted
 * {@code Deque} implementations; in most implementations, insert
 * operations cannot fail.
 *
 * <p>The twelve methods described above are summarized in the
 * following table:<p>
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td></td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
 *  </tr>
 *  <tr>
 *    <td></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Returns special value</em></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Returns special value</em></td>
 *  </tr>
 *  <tr>
 *    <td><b>Insert</b></td>
 *    <td>{@link #addFirst addFirst(e)}</td>
 *    <td>{@link #offerFirst offerFirst(e)}</td>
 *    <td>{@link #addLast addLast(e)}</td>
 *    <td>{@link #offerLast offerLast(e)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Remove</b></td>
 *    <td>{@link #removeFirst removeFirst()}</td>
 *    <td>{@link #pollFirst pollFirst()}</td>
 *    <td>{@link #removeLast removeLast()}</td>
 *    <td>{@link #pollLast pollLast()}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Examine</b></td>
 *    <td>{@link #getFirst getFirst()}</td>
 *    <td>{@link #peekFirst peekFirst()}</td>
 *    <td>{@link #getLast getLast()}</td>
 *    <td>{@link #peekLast peekLast()}</td>
 *  </tr>
 * </table>
 *
 * <p>This interface extends the {@link Queue} interface.  When a deque is
 * used as a queue, FIFO (First-In-First-Out) behavior results.  Elements are
 * added to the end of the deque and removed from the beginning.  The methods
 * inherited from the {@code Queue} interface are precisely equivalent to
 * {@code Deque} methods as indicated in the following table:<p>
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td ALIGN=CENTER> <b>{@code Queue} Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
 *  </tr>
 *  <tr>
 *   <tr>
 *    <td>{@link java.util.Queue#offer offer(e)}</td>
 *    <td>{@link #offerLast offerLast(e)}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#add add(e)}</td>
 *    <td>{@link #addLast addLast(e)}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#poll poll()}</td>
 *    <td>{@link #pollFirst pollFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#remove remove()}</td>
 *    <td>{@link #removeFirst removeFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#peek peek()}</td>
 *    <td>{@link #peek peekFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#element element()}</td>
 *    <td>{@link #getFirst getFirst()}</td>
 *   </tr>
 * </table>
 *
 * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks.  This
 * interface should be used in preference to the legacy {@link Stack} class.
 * When a dequeue is used as a stack, elements are pushed and popped from the
 * beginning of the deque.  Stack methods are precisely equivalent to
 * {@code Deque} methods as indicated in the table below:<p>
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td ALIGN=CENTER> <b>Stack Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
 *  </tr>
 *  <tr>
 *   <tr>
 *    <td>{@link #push push(e)}</td>
 *    <td>{@link #addFirst addFirst(e)}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link #pop pop()}</td>
 *    <td>{@link #removeFirst removeFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link #peek peek()}</td>
 *    <td>{@link #peekFirst peekFirst()}</td>
 *   </tr>
 * </table>
 *
 * <p>Note that the {@link #peek peek} method works equally well when
 * a deque is used as a queue or a stack; in either case, elements are
 * drawn from the beginning of the deque.
 *
 * <p>This interface provides two methods to remove interior
 * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
 * {@link #removeLastOccurrence removeLastOccurrence}.  Unlike the
 * {@link List} interface, this interface does not provide support for
 * indexed access to elements.
 *
 * <p>While {@code Deque} implementations are not strictly required
 * to prohibit the insertion of null elements, they are strongly
 * encouraged to do so.  Users of any {@code Deque} implementations
 * that do allow null elements are strongly encouraged <i>not</i> to
 * take advantage of the ability to insert nulls.  This is so because
 * {@code null} is used as a special return value by various methods
 * to indicated that the deque is empty.
 *
 * <p>{@code Deque} implementations generally do not define
 * element-based versions of the {@code equals} and {@code hashCode}
 * methods, but instead inherit the identity-based versions from class
 * {@code Object}.
 *
 * <p>This interface is a member of the <a
 * href="{@docRoot}/../guide/collections/index.html"> Java Collections
 * Framework</a>.
 *
 * @author Doug Lea
 * @author Josh Bloch
 * @since  1.6
 * @param <E> the type of elements held in this collection
 */
public interface Deque<E> extends Queue<E> {
    /**
     * Inserts the specified element to the front this deque unless it would
     * violate capacity restrictions.  When using a capacity-restricted deque,
     * this method is generally preferable to method {@code addFirst}, which
     * can fail to insert an element only by throwing an exception.
     *
     * @param e the element to insert
     * @return {@code true} if it was possible to insert the element,
     *     else {@code false}
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    boolean offerFirst(E e);

    /**
     * Inserts the specified element to the end of this deque unless it would
     * violate capacity restrictions.  When using a capacity-restricted deque,
     * this method is generally preferable to method {@code addLast} which
     * can fail to insert an element only by throwing an exception.
     *
     * @param e the element to insert
     * @return {@code true} if it was possible to insert the element,
     *     else {@code false}
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    boolean offerLast(E e);

    /**
     * Inserts the specified element to the front of this deque unless it
     * would violate capacity restrictions.
     *
     * @param e the element to insert
     * @throws IllegalStateException if it was not possible to insert
     *    the element due to capacity restrictions
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    void addFirst(E e);

    /**
     * Inserts the specified element to the end of this deque unless it would
     * violate capacity restrictions.
     *
     * @param e the element to insert
     * @throws IllegalStateException if it was not possible to insert
     *    the element due to capacity restrictions
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    void addLast(E e);

    /**
     * Retrieves and removes the first element of this deque, or
     * {@code null} if this deque is empty.
     *
     * @return the first element of this deque, or {@code null} if
     *     this deque is empty
     */
    E pollFirst();

    /**
     * Retrieves and removes the last element of this deque, or
     * {@code null} if this deque is empty.
     *
     * @return the last element of this deque, or {@code null} if
     *     this deque is empty
     */
    E pollLast();

    /**
     * Removes and returns the first element of this deque.  This method
     * differs from the {@code pollFirst} method only in that it throws an
     * exception if this deque is empty.
     *
     * @return the first element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E removeFirst();

    /**
     * Retrieves and removes the last element of this deque.  This method
     * differs from the {@code pollLast} method only in that it throws an
     * exception if this deque is empty.
     *
     * @return the last element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E removeLast();

    /**
     * Retrieves, but does not remove, the first element of this deque,
     * returning {@code null} if this deque is empty.
     *
     * @return the first element of this deque, or {@code null} if
     *     this deque is empty
     */
    E peekFirst();

    /**
     * Retrieves, but does not remove, the last element of this deque,
     * returning {@code null} if this deque is empty.
     *
     * @return the last element of this deque, or {@code null} if this deque
     *     is empty
     */
    E peekLast();

    /**
     * Retrieves, but does not remove, the first element of this
     * deque.  This method differs from the {@code peek} method only
     * in that it throws an exception if this deque is empty.
     *
     * @return the first element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E getFirst();

    /**
     * Retrieves, but does not remove, the last element of this
     * deque.  This method differs from the {@code peek} method only
     * in that it throws an exception if this deque is empty.
     *
     * @return the last element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E getLast();

    /**
     * Removes the first occurrence of the specified element in this
     * deque.  If the deque does not contain the element, it is
     * unchanged.  More formally, removes the first element {@code e}
     * such that {@code (o==null ? e==null : o.equals(e))} (if
     * such an element exists).
     *
     * @param e element to be removed from this deque, if present
     * @return {@code true} if the deque contained the specified element
     * @throws NullPointerException if the specified element is {@code null}
     */
    boolean removeFirstOccurrence(Object e);

    /**
     * Removes the last occurrence of the specified element in this
     * deque.  If the deque does not contain the element, it is
     * unchanged.  More formally, removes the last element {@code e}
     * such that {@code (o==null ? e==null : o.equals(e))} (if
     * such an element exists).
     *
     * @param e element to be removed from this deque, if present
     * @return {@code true} if the deque contained the specified element
     * @throws NullPointerException if the specified element is {@code null}
     */
    boolean removeLastOccurrence(Object e);


    // *** Queue methods ***

    /**
     * Inserts the specified element into the queue represented by this deque
     * unless it would violate capacity restrictions.  In other words, inserts
     * the specified element to the end of this deque.  When using a
     * capacity-restricted deque, this method is generally preferable to the
     * {@link #add} method, which can fail to insert an element only by
     * throwing an exception.
     *
     * <p>This method is equivalent to {@link #offerLast}.
     *
     * @param e the element to insert
     * @return {@code true} if it was possible to insert the element,
     *     else {@code false}
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    boolean offer(E e);

    /**
     * Inserts the specified element into the queue represented by this
     * deque unless it would violate capacity restrictions.  In other words,
     * inserts the specified element as the last element of this deque.
     *
     * <p>This method is equivalent to {@link #addLast}.
     *
     * @param e the element to insert
     * @return {@code true} (as per the spec for {@link Collection#add})
     * @throws IllegalStateException if it was not possible to insert
     *    the element due to capacity restrictions
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    boolean add(E e);

    /**
     * Retrieves and removes the head of the queue represented by
     * this deque, or {@code null} if this deque is empty.  In other words,
     * retrieves and removes the first element of this deque, or {@code null}
     * if this deque is empty.
     *
     * <p>This method is equivalent to {@link #pollFirst()}.
     *
     * @return the first element of this deque, or {@code null} if
     *     this deque is empty
     */
    E poll();

    /**
     * Retrieves and removes the head of the queue represented by this deque.
     * This method differs from the {@code poll} method only in that it
     * throws an exception if this deque is empty.
     *
     * <p>This method is equivalent to {@link #removeFirst()}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E remove();

    /**
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque, returning {@code null} if this deque is empty.
     *
     * <p>This method is equivalent to {@link #peekFirst()}.
     *
     * @return the head of the queue represented by this deque, or
     *     {@code null} if this deque is empty
     */
    E peek();

    /**
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque.  This method differs from the {@code peek} method only in
     * that it throws an exception if this deque is empty.
     *
     * <p>This method is equivalent to {@link #getFirst()}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E element();


    // *** Stack methods ***

    /**
     * Pushes an element onto the stack represented by this deque.  In other
     * words, inserts the element to the front this deque unless it would
     * violate capacity restrictions.
     *
     * <p>This method is equivalent to {@link #addFirst}.
     *
     * @throws IllegalStateException if it was not possible to insert
     *    the element due to capacity restrictions
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    void push(E e);

    /**
     * Pops an element from the stack represented by this deque.  In other
     * words, removes and returns the first element of this deque.
     *
     * <p>This method is equivalent to {@link #removeFirst()}.
     *
     * @return the element at the front of this deque (which is the top
     *     of the stack represented by this deque)
     * @throws NoSuchElementException if this deque is empty
     */
    E pop();


    // *** Collection Method ***

    /**
     * Returns an iterator over the elements in this deque.  The elements
     * will be ordered from first (head) to last (tail).
     *
     * @return an {@code Iterator} over the elements in this deque
     */
    Iterator<E> iterator();
}
Revision:	1.13
Committed:	Sun Jan 18 20:17:33 2015 UTC (9 years, 3 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.12:	+1 -0 lines
Log Message:	exactly one blank line before and after package statements
#	Content
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/publicdomain/zero/1.0/
5	*/
6
7	package jsr166x; // XXX This belongs in java.util!!! XXX
8
9	import java.util.*; // XXX This import goes away XXX
10
11	/**
12	* A linear collection that supports element insertion and removal at
13	* both ends. The name <i>deque</i> is short for "double ended queue"
14	* and is usually pronounced "deck". Most {@code Deque}
15	* implementations place no fixed limits on the number of elements
16	* they may contain, but this interface supports capacity-restricted
17	* deques as well as those with no fixed size limit.
18	*
19	* <p>This interface defines methods to access the elements at both
20	* ends of the deque. Methods are provided to insert, remove, and
21	* examine the element. Each of these methods exists in two forms:
22	* one throws an exception if the operation fails, the other returns a
23	* special value (either {@code null} or {@code false}, depending on
24	* the operation). The latter form of the insert operation is
25	* designed specifically for use with capacity-restricted
26	* {@code Deque} implementations; in most implementations, insert
27	* operations cannot fail.
28	*
29	* <p>The twelve methods described above are summarized in the
30	* following table:<p>
31	*
32	* <table BORDER CELLPADDING=3 CELLSPACING=1>
33	* <tr>
34	* <td></td>
35	* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
36	* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
37	* </tr>
38	* <tr>
39	* <td></td>
40	* <td ALIGN=CENTER><em>Throws exception</em></td>
41	* <td ALIGN=CENTER><em>Returns special value</em></td>
42	* <td ALIGN=CENTER><em>Throws exception</em></td>
43	* <td ALIGN=CENTER><em>Returns special value</em></td>
44	* </tr>
45	* <tr>
46	* <td><b>Insert</b></td>
47	* <td>{@link #addFirst addFirst(e)}</td>
48	* <td>{@link #offerFirst offerFirst(e)}</td>
49	* <td>{@link #addLast addLast(e)}</td>
50	* <td>{@link #offerLast offerLast(e)}</td>
51	* </tr>
52	* <tr>
53	* <td><b>Remove</b></td>
54	* <td>{@link #removeFirst removeFirst()}</td>
55	* <td>{@link #pollFirst pollFirst()}</td>
56	* <td>{@link #removeLast removeLast()}</td>
57	* <td>{@link #pollLast pollLast()}</td>
58	* </tr>
59	* <tr>
60	* <td><b>Examine</b></td>
61	* <td>{@link #getFirst getFirst()}</td>
62	* <td>{@link #peekFirst peekFirst()}</td>
63	* <td>{@link #getLast getLast()}</td>
64	* <td>{@link #peekLast peekLast()}</td>
65	* </tr>
66	* </table>
67	*
68	* <p>This interface extends the {@link Queue} interface. When a deque is
69	* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
70	* added to the end of the deque and removed from the beginning. The methods
71	* inherited from the {@code Queue} interface are precisely equivalent to
72	* {@code Deque} methods as indicated in the following table:<p>
73	*
74	* <table BORDER CELLPADDING=3 CELLSPACING=1>
75	* <tr>
76	* <td ALIGN=CENTER> <b>{@code Queue} Method</b></td>
77	* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
78	* </tr>
79	* <tr>
80	* <tr>
81	* <td>{@link java.util.Queue#offer offer(e)}</td>
82	* <td>{@link #offerLast offerLast(e)}</td>
83	* </tr>
84	* <tr>
85	* <td>{@link java.util.Queue#add add(e)}</td>
86	* <td>{@link #addLast addLast(e)}</td>
87	* </tr>
88	* <tr>
89	* <td>{@link java.util.Queue#poll poll()}</td>
90	* <td>{@link #pollFirst pollFirst()}</td>
91	* </tr>
92	* <tr>
93	* <td>{@link java.util.Queue#remove remove()}</td>
94	* <td>{@link #removeFirst removeFirst()}</td>
95	* </tr>
96	* <tr>
97	* <td>{@link java.util.Queue#peek peek()}</td>
98	* <td>{@link #peek peekFirst()}</td>
99	* </tr>
100	* <tr>
101	* <td>{@link java.util.Queue#element element()}</td>
102	* <td>{@link #getFirst getFirst()}</td>
103	* </tr>
104	* </table>
105	*
106	* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
107	* interface should be used in preference to the legacy {@link Stack} class.
108	* When a dequeue is used as a stack, elements are pushed and popped from the
109	* beginning of the deque. Stack methods are precisely equivalent to
110	* {@code Deque} methods as indicated in the table below:<p>
111	*
112	* <table BORDER CELLPADDING=3 CELLSPACING=1>
113	* <tr>
114	* <td ALIGN=CENTER> <b>Stack Method</b></td>
115	* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
116	* </tr>
117	* <tr>
118	* <tr>
119	* <td>{@link #push push(e)}</td>
120	* <td>{@link #addFirst addFirst(e)}</td>
121	* </tr>
122	* <tr>
123	* <td>{@link #pop pop()}</td>
124	* <td>{@link #removeFirst removeFirst()}</td>
125	* </tr>
126	* <tr>
127	* <td>{@link #peek peek()}</td>
128	* <td>{@link #peekFirst peekFirst()}</td>
129	* </tr>
130	* </table>
131	*
132	* <p>Note that the {@link #peek peek} method works equally well when
133	* a deque is used as a queue or a stack; in either case, elements are
134	* drawn from the beginning of the deque.
135	*
136	* <p>This interface provides two methods to remove interior
137	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
138	* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
139	* {@link List} interface, this interface does not provide support for
140	* indexed access to elements.
141	*
142	* <p>While {@code Deque} implementations are not strictly required
143	* to prohibit the insertion of null elements, they are strongly
144	* encouraged to do so. Users of any {@code Deque} 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	* {@code null} is used as a special return value by various methods
148	* to indicated that the deque is empty.
149	*
150	* <p>{@code Deque} implementations generally do not define
151	* element-based versions of the {@code equals} and {@code hashCode}
152	* methods, but instead inherit the identity-based versions from class
153	* {@code Object}.
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	public interface Deque<E> extends Queue<E> {
165	/**
166	* Inserts the specified element to the front this deque unless it would
167	* violate capacity restrictions. When using a capacity-restricted deque,
168	* this method is generally preferable to method {@code addFirst}, which
169	* can fail to insert an element only by throwing an exception.
170	*
171	* @param e the element to insert
172	* @return {@code true} if it was possible to insert the element,
173	* else {@code false}
174	* @throws NullPointerException if {@code e} is null and this
175	* deque does not permit null elements
176	*/
177	boolean offerFirst(E e);
178
179	/**
180	* Inserts the specified element to the end of this deque unless it would
181	* violate capacity restrictions. When using a capacity-restricted deque,
182	* this method is generally preferable to method {@code addLast} which
183	* can fail to insert an element only by throwing an exception.
184	*
185	* @param e the element to insert
186	* @return {@code true} if it was possible to insert the element,
187	* else {@code false}
188	* @throws NullPointerException if {@code e} is null and this
189	* deque does not permit null elements
190	*/
191	boolean offerLast(E e);
192
193	/**
194	* Inserts the specified element to the front of this deque unless it
195	* would violate capacity restrictions.
196	*
197	* @param e the element to insert
198	* @throws IllegalStateException if it was not possible to insert
199	* the element due to capacity restrictions
200	* @throws NullPointerException if {@code e} is null and this
201	* deque does not permit null elements
202	*/
203	void addFirst(E e);
204
205	/**
206	* Inserts the specified element to the end of this deque unless it would
207	* violate capacity restrictions.
208	*
209	* @param e the element to insert
210	* @throws IllegalStateException if it was not possible to insert
211	* the element due to capacity restrictions
212	* @throws NullPointerException if {@code e} is null and this
213	* deque does not permit null elements
214	*/
215	void addLast(E e);
216
217	/**
218	* Retrieves and removes the first element of this deque, or
219	* {@code null} if this deque is empty.
220	*
221	* @return the first element of this deque, or {@code null} if
222	* this deque is empty
223	*/
224	E pollFirst();
225
226	/**
227	* Retrieves and removes the last element of this deque, or
228	* {@code null} if this deque is empty.
229	*
230	* @return the last element of this deque, or {@code null} if
231	* this deque is empty
232	*/
233	E pollLast();
234
235	/**
236	* Removes and returns the first element of this deque. This method
237	* differs from the {@code pollFirst} method only in that it throws an
238	* exception if this deque is empty.
239	*
240	* @return the first element of this deque
241	* @throws NoSuchElementException if this deque is empty
242	*/
243	E removeFirst();
244
245	/**
246	* Retrieves and removes the last element of this deque. This method
247	* differs from the {@code pollLast} method only in that it throws an
248	* exception if this deque is empty.
249	*
250	* @return the last element of this deque
251	* @throws NoSuchElementException if this deque is empty
252	*/
253	E removeLast();
254
255	/**
256	* Retrieves, but does not remove, the first element of this deque,
257	* returning {@code null} if this deque is empty.
258	*
259	* @return the first element of this deque, or {@code null} if
260	* this deque is empty
261	*/
262	E peekFirst();
263
264	/**
265	* Retrieves, but does not remove, the last element of this deque,
266	* returning {@code null} if this deque is empty.
267	*
268	* @return the last element of this deque, or {@code null} if this deque
269	* is empty
270	*/
271	E peekLast();
272
273	/**
274	* Retrieves, but does not remove, the first element of this
275	* deque. This method differs from the {@code peek} method only
276	* in that it throws an exception if this deque is empty.
277	*
278	* @return the first element of this deque
279	* @throws NoSuchElementException if this deque is empty
280	*/
281	E getFirst();
282
283	/**
284	* Retrieves, but does not remove, the last element of this
285	* deque. This method differs from the {@code peek} method only
286	* in that it throws an exception if this deque is empty.
287	*
288	* @return the last element of this deque
289	* @throws NoSuchElementException if this deque is empty
290	*/
291	E getLast();
292
293	/**
294	* Removes the first occurrence of the specified element in this
295	* deque. If the deque does not contain the element, it is
296	* unchanged. More formally, removes the first element {@code e}
297	* such that {@code (o==null ? e==null : o.equals(e))} (if
298	* such an element exists).
299	*
300	* @param e element to be removed from this deque, if present
301	* @return {@code true} if the deque contained the specified element
302	* @throws NullPointerException if the specified element is {@code null}
303	*/
304	boolean removeFirstOccurrence(Object e);
305
306	/**
307	* Removes the last occurrence of the specified element in this
308	* deque. If the deque does not contain the element, it is
309	* unchanged. More formally, removes the last element {@code e}
310	* such that {@code (o==null ? e==null : o.equals(e))} (if
311	* such an element exists).
312	*
313	* @param e element to be removed from this deque, if present
314	* @return {@code true} if the deque contained the specified element
315	* @throws NullPointerException if the specified element is {@code null}
316	*/
317	boolean removeLastOccurrence(Object e);
318
319
320	// * Queue methods *
321
322	/**
323	* Inserts the specified element into the queue represented by this deque
324	* unless it would violate capacity restrictions. In other words, inserts
325	* the specified element to the end of this deque. When using a
326	* capacity-restricted deque, this method is generally preferable to the
327	* {@link #add} method, which can fail to insert an element only by
328	* throwing an exception.
329	*
330	* <p>This method is equivalent to {@link #offerLast}.
331	*
332	* @param e the element to insert
333	* @return {@code true} if it was possible to insert the element,
334	* else {@code false}
335	* @throws NullPointerException if {@code e} is null and this
336	* deque does not permit null elements
337	*/
338	boolean offer(E e);
339
340	/**
341	* Inserts the specified element into the queue represented by this
342	* deque unless it would violate capacity restrictions. In other words,
343	* inserts the specified element as the last element of this deque.
344	*
345	* <p>This method is equivalent to {@link #addLast}.
346	*
347	* @param e the element to insert
348	* @return {@code true} (as per the spec for {@link Collection#add})
349	* @throws IllegalStateException if it was not possible to insert
350	* the element due to capacity restrictions
351	* @throws NullPointerException if {@code e} is null and this
352	* deque does not permit null elements
353	*/
354	boolean add(E e);
355
356	/**
357	* Retrieves and removes the head of the queue represented by
358	* this deque, or {@code null} if this deque is empty. In other words,
359	* retrieves and removes the first element of this deque, or {@code null}
360	* if this deque is empty.
361	*
362	* <p>This method is equivalent to {@link #pollFirst()}.
363	*
364	* @return the first element of this deque, or {@code null} if
365	* this deque is empty
366	*/
367	E poll();
368
369	/**
370	* Retrieves and removes the head of the queue represented by this deque.
371	* This method differs from the {@code poll} method only in that it
372	* throws an exception if this deque is empty.
373	*
374	* <p>This method is equivalent to {@link #removeFirst()}.
375	*
376	* @return the head of the queue represented by this deque
377	* @throws NoSuchElementException if this deque is empty
378	*/
379	E remove();
380
381	/**
382	* Retrieves, but does not remove, the head of the queue represented by
383	* this deque, returning {@code null} if this deque is empty.
384	*
385	* <p>This method is equivalent to {@link #peekFirst()}.
386	*
387	* @return the head of the queue represented by this deque, or
388	* {@code null} if this deque is empty
389	*/
390	E peek();
391
392	/**
393	* Retrieves, but does not remove, the head of the queue represented by
394	* this deque. This method differs from the {@code peek} method only in
395	* that it throws an exception if this deque is empty.
396	*
397	* <p>This method is equivalent to {@link #getFirst()}.
398	*
399	* @return the head of the queue represented by this deque
400	* @throws NoSuchElementException if this deque is empty
401	*/
402	E element();
403
404
405	// * Stack methods *
406
407	/**
408	* Pushes an element onto the stack represented by this deque. In other
409	* words, inserts the element to the front this deque unless it would
410	* violate capacity restrictions.
411	*
412	* <p>This method is equivalent to {@link #addFirst}.
413	*
414	* @throws IllegalStateException if it was not possible to insert
415	* the element due to capacity restrictions
416	* @throws NullPointerException if {@code e} is null and this
417	* deque does not permit null elements
418	*/
419	void push(E e);
420
421	/**
422	* Pops an element from the stack represented by this deque. In other
423	* words, removes and returns the first element of this deque.
424	*
425	* <p>This method is equivalent to {@link #removeFirst()}.
426	*
427	* @return the element at the front of this deque (which is the top
428	* of the stack represented by this deque)
429	* @throws NoSuchElementException if this deque is empty
430	*/
431	E pop();
432
433
434	// * Collection Method *
435
436	/**
437	* Returns an iterator over the elements in this deque. The elements
438	* will be ordered from first (head) to last (tail).
439	*
440	* @return an {@code Iterator} over the elements in this deque
441	*/
442	Iterator<E> iterator();
443	}