java/util/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/licenses/publicdomain
 */

package java.util;

/**
 * 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 <tt>Deque</tt>
 * 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 <tt>null</tt> or <tt>false</tt>, depending on
 * the operation).  The latter form of the insert operation is
 * designed specifically for use with capacity-restricted
 * <tt>Deque</tt> 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 at the end of the deque and removed from the beginning.  The methods
 * inherited from the <tt>Queue</tt> interface are precisely equivalent to
 * <tt>Deque</tt> methods as indicated in the following table:
 *
 * <p><table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
 *  </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 deque is used as a stack, elements are pushed and popped from the
 * beginning of the deque.  Stack methods are precisely equivalent to
 * <tt>Deque</tt> 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 <tt>Deque</tt> Method</b></td>
 *  </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 <tt>Deque</tt> implementations are not strictly required
 * to prohibit the insertion of null elements, they are strongly
 * encouraged to do so.  Users of any <tt>Deque</tt> 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
 * <tt>null</tt> is used as a special return value by various methods
 * to indicated that the deque is empty.
 *
 * <p><tt>Deque</tt> implementations generally do not define
 * element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
 * methods, but instead inherit the identity-based versions from class
 * <tt>Object</tt>.
 *
 * <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 at the front of this deque unless it would
     * violate capacity restrictions.  When using a capacity-restricted deque,
     * this method is generally preferable to method <tt>addFirst</tt>, which
     * can fail to insert an element only by throwing an exception.
     *
     * @param e the element to insert
     * @return <tt>true</tt> if it was possible to insert the element,
     *     else <tt>false</tt>
     * @throws NullPointerException if the specified element is null and this
     *     deque does not permit null elements
     */
    boolean offerFirst(E e);

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

    /**
     * Inserts the specified element at 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 the specified element is null and this
     *     deque does not permit null elements
     */
    void addFirst(E e);

    /**
     * Inserts the specified element at 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 the specified element is null and this
     *     deque does not permit null elements
     */
    void addLast(E e);

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

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

    /**
     * Retrieves and removes the first element of this deque.  This method
     * differs from the {@link #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 {@link #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 <tt>null</tt> if this deque is empty.
     *
     * @return the first element of this deque, or <tt>null</tt> if
     *     this deque is empty
     */
    E peekFirst();

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

    /**
     * Retrieves, but does not remove, the first element of this
     * deque.  This method differs from the {@link #peekFirst} 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 {@link #peekLast} 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 <tt>e</tt>
     * such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
     * such an element exists).
     *
     * @param o element to be removed from this deque, if present
     * @return <tt>true</tt> if the deque contained the specified element
     * @throws NullPointerException if the specified element is null and this
     *     deque does not permit null elements
     */
    boolean removeFirstOccurrence(Object o);

    /**
     * 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 <tt>e</tt>
     * such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
     * such an element exists).
     *
     * @param o element to be removed from this deque, if present
     * @return <tt>true</tt> if the deque contained the specified element
     * @throws NullPointerException if the specified element is null and this
     *     deque does not permit null elements
     */
    boolean removeLastOccurrence(Object o);


    // *** 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 at 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 <tt>true</tt> if it was possible to insert the element,
     *     else <tt>false</tt>
     * @throws NullPointerException if the specified element 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 <tt>true</tt> (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 the specified element 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 <tt>null</tt> if this deque is empty.  In other words,
     * retrieves and removes the first element of this deque, or <tt>null</tt>
     * if this deque is empty.
     *
     * <p>This method is equivalent to {@link #pollFirst()}.
     *
     * @return the first element of this deque, or <tt>null</tt> if
     *     this deque is empty
     */
    E poll();

    /**
     * Retrieves and removes the head of the queue represented by this deque.
     * This method differs from the {@link #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 <tt>null</tt> if this deque is empty.
     *
     * <p>This method is equivalent to {@link #peekFirst()}.
     *
     * @return the head of the queue represented by this deque, or
     *     <tt>null</tt> 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 {@link #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 at the front of this deque unless it would
     * violate capacity restrictions.
     *
     * <p>This method is equivalent to {@link #addFirst}.
     *
     * @param e the element to push
     * @throws IllegalStateException if it was not possible to insert
     *    the element due to capacity restrictions
     * @throws NullPointerException if the specified element 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 <tt>Iterator</tt> over the elements in this deque
     */
    Iterator<E> iterator();
}
Revision:	1.6
Committed:	Mon May 2 04:19:58 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.5:	+6 -6 lines
Log Message:	doc fixes
#	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/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	* <p>The twelve methods described above are summarized in the
28	* following table:
29	*
30	* <p><table BORDER CELLPADDING=3 CELLSPACING=1>
31	* <tr>
32	* <td></td>
33	* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
34	* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
35	* </tr>
36	* <tr>
37	* <td></td>
38	* <td ALIGN=CENTER><em>Throws exception</em></td>
39	* <td ALIGN=CENTER><em>Returns special value</em></td>
40	* <td ALIGN=CENTER><em>Throws exception</em></td>
41	* <td ALIGN=CENTER><em>Returns special value</em></td>
42	* </tr>
43	* <tr>
44	* <td><b>Insert</b></td>
45	* <td>{@link #addFirst addFirst(e)}</td>
46	* <td>{@link #offerFirst offerFirst(e)}</td>
47	* <td>{@link #addLast addLast(e)}</td>
48	* <td>{@link #offerLast offerLast(e)}</td>
49	* </tr>
50	* <tr>
51	* <td><b>Remove</b></td>
52	* <td>{@link #removeFirst removeFirst()}</td>
53	* <td>{@link #pollFirst pollFirst()}</td>
54	* <td>{@link #removeLast removeLast()}</td>
55	* <td>{@link #pollLast pollLast()}</td>
56	* </tr>
57	* <tr>
58	* <td><b>Examine</b></td>
59	* <td>{@link #getFirst getFirst()}</td>
60	* <td>{@link #peekFirst peekFirst()}</td>
61	* <td>{@link #getLast getLast()}</td>
62	* <td>{@link #peekLast peekLast()}</td>
63	* </tr>
64	* </table>
65	*
66	* <p>This interface extends the {@link Queue} interface. When a deque is
67	* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
68	* added at the end of the deque and removed from the beginning. The methods
69	* inherited from the <tt>Queue</tt> interface are precisely equivalent to
70	* <tt>Deque</tt> methods as indicated in the following table:
71	*
72	* <p><table BORDER CELLPADDING=3 CELLSPACING=1>
73	* <tr>
74	* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
75	* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
76	* </tr>
77	* <tr>
78	* <td>{@link java.util.Queue#offer offer(e)}</td>
79	* <td>{@link #offerLast offerLast(e)}</td>
80	* </tr>
81	* <tr>
82	* <td>{@link java.util.Queue#add add(e)}</td>
83	* <td>{@link #addLast addLast(e)}</td>
84	* </tr>
85	* <tr>
86	* <td>{@link java.util.Queue#poll poll()}</td>
87	* <td>{@link #pollFirst pollFirst()}</td>
88	* </tr>
89	* <tr>
90	* <td>{@link java.util.Queue#remove remove()}</td>
91	* <td>{@link #removeFirst removeFirst()}</td>
92	* </tr>
93	* <tr>
94	* <td>{@link java.util.Queue#peek peek()}</td>
95	* <td>{@link #peek peekFirst()}</td>
96	* </tr>
97	* <tr>
98	* <td>{@link java.util.Queue#element element()}</td>
99	* <td>{@link #getFirst getFirst()}</td>
100	* </tr>
101	* </table>
102	*
103	* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
104	* interface should be used in preference to the legacy {@link Stack} class.
105	* When a deque is used as a stack, elements are pushed and popped from the
106	* beginning of the deque. Stack methods are precisely equivalent to
107	* <tt>Deque</tt> methods as indicated in the table below:
108	*
109	* <p><table BORDER CELLPADDING=3 CELLSPACING=1>
110	* <tr>
111	* <td ALIGN=CENTER> <b>Stack Method</b></td>
112	* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
113	* </tr>
114	* <tr>
115	* <td>{@link #push push(e)}</td>
116	* <td>{@link #addFirst addFirst(e)}</td>
117	* </tr>
118	* <tr>
119	* <td>{@link #pop pop()}</td>
120	* <td>{@link #removeFirst removeFirst()}</td>
121	* </tr>
122	* <tr>
123	* <td>{@link #peek peek()}</td>
124	* <td>{@link #peekFirst peekFirst()}</td>
125	* </tr>
126	* </table>
127	*
128	* <p>Note that the {@link #peek peek} method works equally well when
129	* a deque is used as a queue or a stack; in either case, elements are
130	* drawn from the beginning of the deque.
131	*
132	* <p>This interface provides two methods to remove interior
133	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
134	* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
135	* {@link List} interface, this interface does not provide support for
136	* indexed access to elements.
137	*
138	* <p>While <tt>Deque</tt> implementations are not strictly required
139	* to prohibit the insertion of null elements, they are strongly
140	* encouraged to do so. Users of any <tt>Deque</tt> implementations
141	* that do allow null elements are strongly encouraged <i>not</i> to
142	* take advantage of the ability to insert nulls. This is so because
143	* <tt>null</tt> is used as a special return value by various methods
144	* to indicated that the deque is empty.
145	*
146	* <p><tt>Deque</tt> implementations generally do not define
147	* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
148	* methods, but instead inherit the identity-based versions from class
149	* <tt>Object</tt>.
150	*
151	* <p>This interface is a member of the <a
152	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
153	* Framework</a>.
154	*
155	* @author Doug Lea
156	* @author Josh Bloch
157	* @since 1.6
158	* @param <E> the type of elements held in this collection
159	*/
160
161	public interface Deque<E> extends Queue<E> {
162	/**
163	* Inserts the specified element at the front of this deque unless it would
164	* violate capacity restrictions. When using a capacity-restricted deque,
165	* this method is generally preferable to method <tt>addFirst</tt>, which
166	* can fail to insert an element only by throwing an exception.
167	*
168	* @param e the element to insert
169	* @return <tt>true</tt> if it was possible to insert the element,
170	* else <tt>false</tt>
171	* @throws NullPointerException if the specified element is null and this
172	* deque does not permit null elements
173	*/
174	boolean offerFirst(E e);
175
176	/**
177	* Inserts the specified element at the end of this deque unless it would
178	* violate capacity restrictions. When using a capacity-restricted deque,
179	* this method is generally preferable to method <tt>addLast</tt> which
180	* can fail to insert an element only by throwing an exception.
181	*
182	* @param e the element to insert
183	* @return <tt>true</tt> if it was possible to insert the element,
184	* else <tt>false</tt>
185	* @throws NullPointerException if the specified element is null and this
186	* deque does not permit null elements
187	*/
188	boolean offerLast(E e);
189
190	/**
191	* Inserts the specified element at the front of this deque unless it
192	* would violate capacity restrictions.
193	*
194	* @param e the element to insert
195	* @throws IllegalStateException if it was not possible to insert
196	* the element due to capacity restrictions
197	* @throws NullPointerException if the specified element is null and this
198	* deque does not permit null elements
199	*/
200	void addFirst(E e);
201
202	/**
203	* Inserts the specified element at the end of this deque unless it would
204	* violate capacity restrictions.
205	*
206	* @param e the element to insert
207	* @throws IllegalStateException if it was not possible to insert
208	* the element due to capacity restrictions
209	* @throws NullPointerException if the specified element is null and this
210	* deque does not permit null elements
211	*/
212	void addLast(E e);
213
214	/**
215	* Retrieves and removes the first element of this deque, or
216	* <tt>null</tt> if this deque is empty.
217	*
218	* @return the first element of this deque, or <tt>null</tt> if
219	* this deque is empty
220	*/
221	E pollFirst();
222
223	/**
224	* Retrieves and removes the last element of this deque, or
225	* <tt>null</tt> if this deque is empty.
226	*
227	* @return the last element of this deque, or <tt>null</tt> if
228	* this deque is empty
229	*/
230	E pollLast();
231
232	/**
233	* Retrieves and removes the first element of this deque. This method
234	* differs from the {@link #pollFirst} method only in that it throws an
235	* exception if this deque is empty.
236	*
237	* @return the first element of this deque
238	* @throws NoSuchElementException if this deque is empty
239	*/
240	E removeFirst();
241
242	/**
243	* Retrieves and removes the last element of this deque. This method
244	* differs from the {@link #pollLast} method only in that it throws an
245	* exception if this deque is empty.
246	*
247	* @return the last element of this deque
248	* @throws NoSuchElementException if this deque is empty
249	*/
250	E removeLast();
251
252	/**
253	* Retrieves, but does not remove, the first element of this deque,
254	* returning <tt>null</tt> if this deque is empty.
255	*
256	* @return the first element of this deque, or <tt>null</tt> if
257	* this deque is empty
258	*/
259	E peekFirst();
260
261	/**
262	* Retrieves, but does not remove, the last element of this deque,
263	* returning <tt>null</tt> if this deque is empty.
264	*
265	* @return the last element of this deque, or <tt>null</tt> if this deque
266	* is empty
267	*/
268	E peekLast();
269
270	/**
271	* Retrieves, but does not remove, the first element of this
272	* deque. This method differs from the {@link #peekFirst} method only
273	* in that it throws an exception if this deque is empty.
274	*
275	* @return the first element of this deque
276	* @throws NoSuchElementException if this deque is empty
277	*/
278	E getFirst();
279
280	/**
281	* Retrieves, but does not remove, the last element of this
282	* deque. This method differs from the {@link #peekLast} method only
283	* in that it throws an exception if this deque is empty.
284	*
285	* @return the last element of this deque
286	* @throws NoSuchElementException if this deque is empty
287	*/
288	E getLast();
289
290	/**
291	* Removes the first occurrence of the specified element in this
292	* deque. If the deque does not contain the element, it is
293	* unchanged. More formally, removes the first element <tt>e</tt>
294	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
295	* such an element exists).
296	*
297	* @param o element to be removed from this deque, if present
298	* @return <tt>true</tt> if the deque contained the specified element
299	* @throws NullPointerException if the specified element is null and this
300	* deque does not permit null elements
301	*/
302	boolean removeFirstOccurrence(Object o);
303
304	/**
305	* Removes the last occurrence of the specified element in this
306	* deque. If the deque does not contain the element, it is
307	* unchanged. More formally, removes the last element <tt>e</tt>
308	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
309	* such an element exists).
310	*
311	* @param o element to be removed from this deque, if present
312	* @return <tt>true</tt> if the deque contained the specified element
313	* @throws NullPointerException if the specified element is null and this
314	* deque does not permit null elements
315	*/
316	boolean removeLastOccurrence(Object o);
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 at 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 the specified element 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 the specified element 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 {@link #poll} 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	* 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	E peek();
390
391	/**
392	* Retrieves, but does not remove, the head of the queue represented by
393	* this deque. This method differs from the {@link #peek} 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	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 at the front of this deque unless it would
409	* violate capacity restrictions.
410	*
411	* <p>This method is equivalent to {@link #addFirst}.
412	*
413	* @param e the element to push
414	* @throws IllegalStateException if it was not possible to insert
415	* the element due to capacity restrictions
416	* @throws NullPointerException if the specified element 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 <tt>Iterator</tt> over the elements in this deque
441	*/
442	Iterator<E> iterator();
443	}