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:	1.7
Committed:	Mon May 2 17:34:02 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.6:	+6 -3 lines
Log Message:	<p> before <table>
#	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>
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 at 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:
72	*
73	* <p>
74	* <table BORDER CELLPADDING=3 CELLSPACING=1>
75	* <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	* <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 deque 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:
110	*
111	* <p>
112	* <table BORDER CELLPADDING=3 CELLSPACING=1>
113	* <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	* </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 interface provides two methods 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 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
164	public interface Deque<E> extends Queue<E> {
165	/**
166	* Inserts the specified element at the front of this deque unless it would
167	* violate capacity restrictions. When using a capacity-restricted deque,
168	* this method is generally preferable to method <tt>addFirst</tt>, which
169	* can fail to insert an element only by throwing an exception.
170	*
171	* @param e the element to insert
172	* @return <tt>true</tt> if it was possible to insert the element,
173	* else <tt>false</tt>
174	* @throws NullPointerException if the specified element is null and this
175	* deque does not permit null elements
176	*/
177	boolean offerFirst(E e);
178
179	/**
180	* Inserts the specified element at 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 <tt>addLast</tt> which
183	* can fail to insert an element only by throwing an exception.
184	*
185	* @param e the element to insert
186	* @return <tt>true</tt> if it was possible to insert the element,
187	* else <tt>false</tt>
188	* @throws NullPointerException if the specified element is null and this
189	* deque does not permit null elements
190	*/
191	boolean offerLast(E e);
192
193	/**
194	* Inserts the specified element at 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 the specified element is null and this
201	* deque does not permit null elements
202	*/
203	void addFirst(E e);
204
205	/**
206	* Inserts the specified element at 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 the specified element 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	* <tt>null</tt> if this deque is empty.
220	*
221	* @return the first element of this deque, or <tt>null</tt> if
222	* this deque is empty
223	*/
224	E pollFirst();
225
226	/**
227	* Retrieves and removes the last element of this deque, or
228	* <tt>null</tt> if this deque is empty.
229	*
230	* @return the last element of this deque, or <tt>null</tt> if
231	* this deque is empty
232	*/
233	E pollLast();
234
235	/**
236	* Retrieves and removes the first element of this deque. This method
237	* differs from the {@link #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 {@link #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 <tt>null</tt> if this deque is empty.
258	*
259	* @return the first element of this deque, or <tt>null</tt> 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 <tt>null</tt> if this deque is empty.
267	*
268	* @return the last element of this deque, or <tt>null</tt> 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 {@link #peekFirst} 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 {@link #peekLast} 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 <tt>e</tt>
297	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
298	* such an element exists).
299	*
300	* @param o element to be removed from this deque, if present
301	* @return <tt>true</tt> if the deque contained the specified element
302	* @throws NullPointerException if the specified element is null and this
303	* deque does not permit null elements
304	*/
305	boolean removeFirstOccurrence(Object o);
306
307	/**
308	* Removes the last occurrence of the specified element in this
309	* deque. If the deque does not contain the element, it is
310	* unchanged. More formally, removes the last element <tt>e</tt>
311	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
312	* such an element exists).
313	*
314	* @param o element to be removed from this deque, if present
315	* @return <tt>true</tt> if the deque contained the specified element
316	* @throws NullPointerException if the specified element is null and this
317	* deque does not permit null elements
318	*/
319	boolean removeLastOccurrence(Object o);
320
321
322	// * Queue methods *
323
324	/**
325	* Inserts the specified element into the queue represented by this deque
326	* unless it would violate capacity restrictions. In other words, inserts
327	* the specified element at the end of this deque. When using a
328	* capacity-restricted deque, this method is generally preferable to the
329	* {@link #add} method, which can fail to insert an element only by
330	* throwing an exception.
331	*
332	* <p>This method is equivalent to {@link #offerLast}.
333	*
334	* @param e the element to insert
335	* @return <tt>true</tt> if it was possible to insert the element,
336	* else <tt>false</tt>
337	* @throws NullPointerException if the specified element is null and this
338	* deque does not permit null elements
339	*/
340	boolean offer(E e);
341
342	/**
343	* Inserts the specified element into the queue represented by this
344	* deque unless it would violate capacity restrictions. In other words,
345	* inserts the specified element as the last element of this deque.
346	*
347	* <p>This method is equivalent to {@link #addLast}.
348	*
349	* @param e the element to insert
350	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
351	* @throws IllegalStateException if it was not possible to insert
352	* the element due to capacity restrictions
353	* @throws NullPointerException if the specified element is null and this
354	* deque does not permit null elements
355	*/
356	boolean add(E e);
357
358	/**
359	* Retrieves and removes the head of the queue represented by
360	* this deque, or <tt>null</tt> if this deque is empty. In other words,
361	* retrieves and removes the first element of this deque, or <tt>null</tt>
362	* if this deque is empty.
363	*
364	* <p>This method is equivalent to {@link #pollFirst()}.
365	*
366	* @return the first element of this deque, or <tt>null</tt> if
367	* this deque is empty
368	*/
369	E poll();
370
371	/**
372	* Retrieves and removes the head of the queue represented by this deque.
373	* This method differs from the {@link #poll} method only in that it
374	* throws an exception if this deque is empty.
375	*
376	* <p>This method is equivalent to {@link #removeFirst()}.
377	*
378	* @return the head of the queue represented by this deque
379	* @throws NoSuchElementException if this deque is empty
380	*/
381	E remove();
382
383	/**
384	* Retrieves, but does not remove, the head of the queue represented by
385	* this deque, returning <tt>null</tt> if this deque is empty.
386	*
387	* <p>This method is equivalent to {@link #peekFirst()}.
388	*
389	* @return the head of the queue represented by this deque, or
390	* <tt>null</tt> if this deque is empty
391	*/
392	E peek();
393
394	/**
395	* Retrieves, but does not remove, the head of the queue represented by
396	* this deque. This method differs from the {@link #peek} method only in
397	* that it throws an exception if this deque is empty.
398	*
399	* <p>This method is equivalent to {@link #getFirst()}.
400	*
401	* @return the head of the queue represented by this deque
402	* @throws NoSuchElementException if this deque is empty
403	*/
404	E element();
405
406
407	// * Stack methods *
408
409	/**
410	* Pushes an element onto the stack represented by this deque. In other
411	* words, inserts the element at the front of this deque unless it would
412	* violate capacity restrictions.
413	*
414	* <p>This method is equivalent to {@link #addFirst}.
415	*
416	* @param e the element to push
417	* @throws IllegalStateException if it was not possible to insert
418	* the element due to capacity restrictions
419	* @throws NullPointerException if the specified element is null and this
420	* deque does not permit null elements
421	*/
422	void push(E e);
423
424	/**
425	* Pops an element from the stack represented by this deque. In other
426	* words, removes and returns the first element of this deque.
427	*
428	* <p>This method is equivalent to {@link #removeFirst()}.
429	*
430	* @return the element at the front of this deque (which is the top
431	* of the stack represented by this deque)
432	* @throws NoSuchElementException if this deque is empty
433	*/
434	E pop();
435
436
437	// * Collection Method *
438
439	/**
440	* Returns an iterator over the elements in this deque. The elements
441	* will be ordered from first (head) to last (tail).
442	*
443	* @return an <tt>Iterator</tt> over the elements in this deque
444	*/
445	Iterator<E> iterator();
446	}