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 to 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>
 *   <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
 * <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>
 *   <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 to the front 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 <tt>e</tt> 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 <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 <tt>e</tt> 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 <tt>e</tt> 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 <tt>e</tt> 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();

    /**
     * Removes and returns the first element of this deque.  This method
     * differs from the <tt>pollFirst</tt> 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 <tt>pollLast</tt> 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 <tt>peek</tt> 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 <tt>peek</tt> 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 e 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 <tt>null</tt>
     */
    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 <tt>e</tt>
     * such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
     * such an element exists).
     *
     * @param e 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 <tt>null</tt>
     */
    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 <tt>true</tt> if it was possible to insert the element,
     *     else <tt>false</tt>
     * @throws NullPointerException if <tt>e</tt> 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 <tt>e</tt> 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 <tt>poll</tt> 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 <tt>peek</tt> 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 <tt>e</tt> 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:	1.2
Committed:	Tue Mar 8 12:27:06 2005 UTC (19 years, 2 months ago) by dl
Branch:	MAIN
Changes since 1.1:	+4 -4 lines
Log Message:	Copyedit pass
#	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:<p>
29	*
30	* <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 to 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:<p>
71	*
72	* <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	* <tr>
79	* <td>{@link java.util.Queue#offer offer(e)}</td>
80	* <td>{@link #offerLast offerLast(e)}</td>
81	* </tr>
82	* <tr>
83	* <td>{@link java.util.Queue#add add(e)}</td>
84	* <td>{@link #addLast addLast(e)}</td>
85	* </tr>
86	* <tr>
87	* <td>{@link java.util.Queue#poll poll()}</td>
88	* <td>{@link #pollFirst pollFirst()}</td>
89	* </tr>
90	* <tr>
91	* <td>{@link java.util.Queue#remove remove()}</td>
92	* <td>{@link #removeFirst removeFirst()}</td>
93	* </tr>
94	* <tr>
95	* <td>{@link java.util.Queue#peek peek()}</td>
96	* <td>{@link #peek peekFirst()}</td>
97	* </tr>
98	* <tr>
99	* <td>{@link java.util.Queue#element element()}</td>
100	* <td>{@link #getFirst getFirst()}</td>
101	* </tr>
102	* </table>
103	*
104	* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
105	* interface should be used in preference to the legacy {@link Stack} class.
106	* When a dequeue is used as a stack, elements are pushed and popped from the
107	* beginning of the deque. Stack methods are precisely equivalent to
108	* <tt>Deque</tt> methods as indicated in the table below:<p>
109	*
110	* <table BORDER CELLPADDING=3 CELLSPACING=1>
111	* <tr>
112	* <td ALIGN=CENTER> <b>Stack Method</b></td>
113	* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
114	* </tr>
115	* <tr>
116	* <tr>
117	* <td>{@link #push push(e)}</td>
118	* <td>{@link #addFirst addFirst(e)}</td>
119	* </tr>
120	* <tr>
121	* <td>{@link #pop pop()}</td>
122	* <td>{@link #removeFirst removeFirst()}</td>
123	* </tr>
124	* <tr>
125	* <td>{@link #peek peek()}</td>
126	* <td>{@link #peekFirst peekFirst()}</td>
127	* </tr>
128	* </table>
129	*
130	* <p>Note that the {@link #peek peek} method works equally well when
131	* a deque is used as a queue or a stack; in either case, elements are
132	* drawn from the beginning of the deque.
133	*
134	* <p>This interface provides two methods to remove interior
135	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
136	* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
137	* {@link List} interface, this interface does not provide support for
138	* indexed access to elements.
139	*
140	* <p>While <tt>Deque</tt> implementations are not strictly required
141	* to prohibit the insertion of null elements, they are strongly
142	* encouraged to do so. Users of any <tt>Deque</tt> implementations
143	* that do allow null elements are strongly encouraged <i>not</i> to
144	* take advantage of the ability to insert nulls. This is so because
145	* <tt>null</tt> is used as a special return value by various methods
146	* to indicated that the deque is empty.
147	*
148	* <p><tt>Deque</tt> implementations generally do not define
149	* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
150	* methods, but instead inherit the identity-based versions from class
151	* <tt>Object</tt>.
152	*
153	* <p>This interface is a member of the <a
154	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
155	* Framework</a>.
156	*
157	* @author Doug Lea
158	* @author Josh Bloch
159	* @since 1.6
160	* @param <E> the type of elements held in this collection
161	*/
162
163	public interface Deque<E> extends Queue<E> {
164	/**
165	* Inserts the specified element to the front this deque unless it would
166	* violate capacity restrictions. When using a capacity-restricted deque,
167	* this method is generally preferable to method <tt>addFirst</tt>, which
168	* can fail to insert an element only by throwing an exception.
169	*
170	* @param e the element to insert
171	* @return <tt>true</tt> if it was possible to insert the element,
172	* else <tt>false</tt>
173	* @throws NullPointerException if <tt>e</tt> is null and this
174	* deque does not permit null elements
175	*/
176	boolean offerFirst(E e);
177
178	/**
179	* Inserts the specified element to the end of this deque unless it would
180	* violate capacity restrictions. When using a capacity-restricted deque,
181	* this method is generally preferable to method <tt>addLast</tt> which
182	* can fail to insert an element only by throwing an exception.
183	*
184	* @param e the element to insert
185	* @return <tt>true</tt> if it was possible to insert the element,
186	* else <tt>false</tt>
187	* @throws NullPointerException if <tt>e</tt> is null and this
188	* deque does not permit null elements
189	*/
190	boolean offerLast(E e);
191
192	/**
193	* Inserts the specified element to the front of this deque unless it
194	* would violate capacity restrictions.
195	*
196	* @param e the element to insert
197	* @throws IllegalStateException if it was not possible to insert
198	* the element due to capacity restrictions
199	* @throws NullPointerException if <tt>e</tt> is null and this
200	* deque does not permit null elements
201	*/
202	void addFirst(E e);
203
204	/**
205	* Inserts the specified element to the end of this deque unless it would
206	* violate capacity restrictions.
207	*
208	* @param e the element to insert
209	* @throws IllegalStateException if it was not possible to insert
210	* the element due to capacity restrictions
211	* @throws NullPointerException if <tt>e</tt> is null and this
212	* deque does not permit null elements
213	*/
214	void addLast(E e);
215
216	/**
217	* Retrieves and removes the first element of this deque, or
218	* <tt>null</tt> if this deque is empty.
219	*
220	* @return the first element of this deque, or <tt>null</tt> if
221	* this deque is empty
222	*/
223	E pollFirst();
224
225	/**
226	* Retrieves and removes the last element of this deque, or
227	* <tt>null</tt> if this deque is empty.
228	*
229	* @return the last element of this deque, or <tt>null</tt> if
230	* this deque is empty
231	*/
232	E pollLast();
233
234	/**
235	* Removes and returns the first element of this deque. This method
236	* differs from the <tt>pollFirst</tt> method only in that it throws an
237	* exception if this deque is empty.
238	*
239	* @return the first element of this deque
240	* @throws NoSuchElementException if this deque is empty
241	*/
242	E removeFirst();
243
244	/**
245	* Retrieves and removes the last element of this deque. This method
246	* differs from the <tt>pollLast</tt> method only in that it throws an
247	* exception if this deque is empty.
248	*
249	* @return the last element of this deque
250	* @throws NoSuchElementException if this deque is empty
251	*/
252	E removeLast();
253
254	/**
255	* Retrieves, but does not remove, the first element of this deque,
256	* returning <tt>null</tt> if this deque is empty.
257	*
258	* @return the first element of this deque, or <tt>null</tt> if
259	* this deque is empty
260	*/
261	E peekFirst();
262
263	/**
264	* Retrieves, but does not remove, the last element of this deque,
265	* returning <tt>null</tt> if this deque is empty.
266	*
267	* @return the last element of this deque, or <tt>null</tt> if this deque
268	* is empty
269	*/
270	E peekLast();
271
272	/**
273	* Retrieves, but does not remove, the first element of this
274	* deque. This method differs from the <tt>peek</tt> method only
275	* in that it throws an exception if this deque is empty.
276	*
277	* @return the first element of this deque
278	* @throws NoSuchElementException if this deque is empty
279	*/
280	E getFirst();
281
282	/**
283	* Retrieves, but does not remove, the last element of this
284	* deque. This method differs from the <tt>peek</tt> method only
285	* in that it throws an exception if this deque is empty.
286	*
287	* @return the last element of this deque
288	* @throws NoSuchElementException if this deque is empty
289	*/
290	E getLast();
291
292	/**
293	* Removes the first occurrence of the specified element in this
294	* deque. If the deque does not contain the element, it is
295	* unchanged. More formally, removes the first element <tt>e</tt>
296	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
297	* such an element exists).
298	*
299	* @param e element to be removed from this deque, if present
300	* @return <tt>true</tt> if the deque contained the specified element
301	* @throws NullPointerException if the specified element is <tt>null</tt>
302	*/
303	boolean removeFirstOccurrence(Object e);
304
305	/**
306	* Removes the last occurrence of the specified element in this
307	* deque. If the deque does not contain the element, it is
308	* unchanged. More formally, removes the last element <tt>e</tt>
309	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
310	* such an element exists).
311	*
312	* @param e element to be removed from this deque, if present
313	* @return <tt>true</tt> if the deque contained the specified element
314	* @throws NullPointerException if the specified element is <tt>null</tt>
315	*/
316	boolean removeLastOccurrence(Object e);
317
318
319	// * Queue methods *
320
321	/**
322	* Inserts the specified element into the queue represented by this deque
323	* unless it would violate capacity restrictions. In other words, inserts
324	* the specified element to the end of this deque. When using a
325	* capacity-restricted deque, this method is generally preferable to the
326	* {@link #add} method, which can fail to insert an element only by
327	* throwing an exception.
328	*
329	* <p>This method is equivalent to {@link #offerLast}.
330	*
331	* @param e the element to insert
332	* @return <tt>true</tt> if it was possible to insert the element,
333	* else <tt>false</tt>
334	* @throws NullPointerException if <tt>e</tt> is null and this
335	* deque does not permit null elements
336	*/
337	boolean offer(E e);
338
339	/**
340	* Inserts the specified element into the queue represented by this
341	* deque unless it would violate capacity restrictions. In other words,
342	* inserts the specified element as the last element of this deque.
343	*
344	* <p>This method is equivalent to {@link #addLast}.
345	*
346	* @param e the element to insert
347	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
348	* @throws IllegalStateException if it was not possible to insert
349	* the element due to capacity restrictions
350	* @throws NullPointerException if <tt>e</tt> is null and this
351	* deque does not permit null elements
352	*/
353	boolean add(E e);
354
355	/**
356	* Retrieves and removes the head of the queue represented by
357	* this deque, or <tt>null</tt> if this deque is empty. In other words,
358	* retrieves and removes the first element of this deque, or <tt>null</tt>
359	* if this deque is empty.
360	*
361	* <p>This method is equivalent to {@link #pollFirst()}.
362	*
363	* @return the first element of this deque, or <tt>null</tt> if
364	* this deque is empty
365	*/
366	E poll();
367
368	/**
369	* Retrieves and removes the head of the queue represented by this deque.
370	* This method differs from the <tt>poll</tt> method only in that it
371	* throws an exception if this deque is empty.
372	*
373	* <p>This method is equivalent to {@link #removeFirst()}.
374	*
375	* @return the head of the queue represented by this deque
376	* @throws NoSuchElementException if this deque is empty
377	*/
378	E remove();
379
380	/**
381	* 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 <tt>peek</tt> method only in
394	* that it throws an exception if this deque is empty.
395	*
396	* <p>This method is equivalent to {@link #getFirst()}
397	*
398	* @return the head of the queue represented by this deque
399	* @throws NoSuchElementException if this deque is empty
400	*/
401	E element();
402
403
404	// * Stack methods *
405
406	/**
407	* Pushes an element onto the stack represented by this deque. In other
408	* words, inserts the element to the front this deque unless it would
409	* violate capacity restrictions.
410	*
411	* <p>This method is equivalent to {@link #addFirst}.
412	*
413	* @throws IllegalStateException if it was not possible to insert
414	* the element due to capacity restrictions
415	* @throws NullPointerException if <tt>e</tt> is null and this
416	* deque does not permit null elements
417	*/
418	void push(E e);
419
420	/**
421	* Pops an element from the stack represented by this deque. In other
422	* words, removes and returns the first element of this deque.
423	*
424	* <p>This method is equivalent to {@link #removeFirst()}.
425	*
426	* @return the element at the front of this deque (which is the top
427	* of the stack represented by this deque)
428	* @throws NoSuchElementException if this deque is empty
429	*/
430	E pop();
431
432
433	// * Collection Method *
434
435	/**
436	* Returns an iterator over the elements in this deque. The elements
437	* will be ordered from first (head) to last (tail).
438	*
439	* @return an <tt>Iterator</tt> over the elements in this deque
440	*/
441	Iterator<E> iterator();
442	}