src/jsr166x/Deque.java

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

package jsr166x;     // XXX This belongs in java.util!!! XXX
import java.util.*;    // XXX This import goes away        XXX

/**
 * A linear collection that supports element insertion and removal
 * at both ends.  The name <i>deque</i> is short for "double ended
 * queue" and is usually pronounced "deck".  Most <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 are summarized in the 
 * follwoing 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 #firstElement firstElement()}</td>
 *    <td>{@link #peekFirst peekFirst()}</td>
 *    <td>{@link #lastElement lastElement()}</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 #firstElement firstElement()}</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 inteface provides two methods to 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 firstElement();

    /**
     * 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 lastElement();

    /**
     * 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 #firstElement()}
     *
     * @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 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:	1.3
Committed:	Sun Dec 5 21:15:31 2004 UTC (19 years, 5 months ago) by dl
Branch:	MAIN
Changes since 1.2:	+323 -116 lines
Log Message:	Revised Deque interface; new BlockingDeque interface and implementations
#	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 jsr166x; // XXX This belongs in java.util!!! XXX
8	import java.util.*; // XXX This import goes away XXX
9
10	/**
11	* A linear collection that supports element insertion and removal
12	* at both ends. The name <i>deque</i> is short for "double ended
13	* queue" and is usually pronounced "deck". Most <tt>Deque</tt>
14	* implementations place no fixed limits on the number of elements
15	* they may contain, but this interface supports capacity-restricted
16	* deques as well as those with no fixed size limit.
17	*
18	* <p>This interface defines methods to access the elements at both ends of
19	* the deque. Methods are provided to insert, remove, and examine the
20	* element. Each of these methods exists in two forms: one throws an
21	* exception if the operation fails, the other returns a special value (either
22	* <tt>null</tt> or <tt>false</tt>, depending on the operation). The latter
23	* form of the insert operation is designed specifically for use with
24	* capacity-restricted <tt>Deque</tt> implementations; in most implementations,
25	* insert operations cannot fail.
26	*
27	* <p>The twelve methods described above are are summarized in the
28	* follwoing 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 #firstElement firstElement()}</td>
60	* <td>{@link #peekFirst peekFirst()}</td>
61	* <td>{@link #lastElement lastElement()}</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 #firstElement firstElement()}</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	* <p>Note that the {@link #peek peek} method works equally well when a deque
130	* is used as a queue or a stack; in either case, elements are drawn from the
131	* beginning of the deque.
132	*
133	* <p>This inteface provides two methods to to remove interior elements,
134	* {@link #removeFirstOccurrence removeFirstOccurrence} and {@link
135	* #removeLastOccurrence removeLastOccurrence}. Unlike the {@link List}
136	* interface, this interface does not provide support for indexed access to
137	* elements.
138	*
139	* <p>While <tt>Deque</tt> implementations are not strictly required to
140	* prohibit the insertion of null elements, they are strongly encouraged to do
141	* so. Users of any <tt>Deque</tt> implementations that do allow null
142	* elements are strongly encouraged <i>not</i> to take advantage of the
143	* ability to insert nulls. This is so because <tt>null</tt> is used as a
144	* special return value by various methods to indicated that the deque is
145	* empty.
146	*
147	* <p><tt>Deque</tt> implementations generally do not define
148	* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
149	* methods, but instead inherit the identity-based versions from class
150	* <tt>Object</tt>.
151	*
152	* <p>This interface is a member of the <a
153	* href="{@docRoot}/../guide/collections/index.html"> Java Collections
154	* Framework</a>.
155	*
156	* @author Doug Lea
157	* @author Josh Bloch
158	* @since 1.6
159	* @param <E> the type of elements held in this collection
160	*/
161	public interface Deque<E> extends Queue<E> {
162	/**
163	* Inserts the specified element to the front 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 <tt>e</tt> is null and this
172	* deque does not permit null elements
173	*/
174	boolean offerFirst(E e);
175
176	/**
177	* Inserts the specified element to 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 <tt>e</tt> is null and this
186	* deque does not permit null elements
187	*/
188	boolean offerLast(E e);
189
190	/**
191	* Inserts the specified element to 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 <tt>e</tt> is null and this
198	* deque does not permit null elements
199	*/
200	void addFirst(E e);
201
202	/**
203	* Inserts the specified element to 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 <tt>e</tt> 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	* Removes and returns the first element of this deque. This method
234	* differs from the <tt>pollFirst</tt> 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 <tt>pollLast</tt> 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 <tt>peek</tt> 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 firstElement();
279
280	/**
281	* Retrieves, but does not remove, the last element of this
282	* deque. This method differs from the <tt>peek</tt> 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 lastElement();
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 e 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 <tt>null</tt>
300	*/
301	boolean removeFirstOccurrence(Object e);
302
303	/**
304	* Removes the last occurrence of the specified element in this
305	* deque. If the deque does not contain the element, it is
306	* unchanged. More formally, removes the last element <tt>e</tt>
307	* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
308	* such an element exists).
309	*
310	* @param e element to be removed from this deque, if present
311	* @return <tt>true</tt> if the deque contained the specified element
312	* @throws NullPointerException if the specified element is <tt>null</tt>
313	*/
314	boolean removeLastOccurrence(Object e);
315
316
317	// * Queue methods *
318
319	/**
320	* Inserts the specified element into the queue represented by this deque
321	* unless it would violate capacity restrictions. In other words, inserts
322	* the specified element to the end of this deque. When using a
323	* capacity-restricted deque, this method is generally preferable to the
324	* {@link #add} method, which can fail to insert an element only by
325	* throwing an exception.
326	*
327	* <p>This method is equivalent to {@link #offerLast}.
328	*
329	* @param e the element to insert
330	* @return <tt>true</tt> if it was possible to insert the element,
331	* else <tt>false</tt>
332	* @throws NullPointerException if <tt>e</tt> is null and this
333	* deque does not permit null elements
334	*/
335	boolean offer(E e);
336
337	/**
338	* Inserts the specified element into the queue represented by this
339	* deque unless it would violate capacity restrictions. In other words,
340	* inserts the specified element as the last element of this deque.
341	*
342	* <p>This method is equivalent to {@link #addLast}.
343	*
344	* @param e the element to insert
345	* @return <tt>true</tt> (as per the spec for {@link Collection#add})
346	* @throws IllegalStateException if it was not possible to insert
347	* the element due to capacity restrictions
348	* @throws NullPointerException if <tt>e</tt> is null and this
349	* deque does not permit null elements
350	*/
351	boolean add(E e);
352
353	/**
354	* Retrieves and removes the head of the queue represented by
355	* this deque, or <tt>null</tt> if this deque is empty. In other words,
356	* retrieves and removes the first element of this deque, or <tt>null</tt>
357	* if this deque is empty.
358	*
359	* <p>This method is equivalent to {@link #pollFirst()}.
360	*
361	* @return the first element of this deque, or <tt>null</tt> if
362	* this deque is empty
363	*/
364	E poll();
365
366	/**
367	* Retrieves and removes the head of the queue represented by this deque.
368	* This method differs from the <tt>poll</tt> method only in that it
369	* throws an exception if this deque is empty.
370	*
371	* <p>This method is equivalent to {@link #removeFirst()}.
372	*
373	* @return the head of the queue represented by this deque
374	* @throws NoSuchElementException if this deque is empty
375	*/
376	E remove();
377
378	/**
379	* Retrieves, but does not remove, the head of the queue represented by
380	* this deque, returning <tt>null</tt> if this deque is empty.
381	*
382	* <p>This method is equivalent to {@link #peekFirst()}
383	*
384	* @return the head of the queue represented by this deque, or
385	* <tt>null</tt> if this deque is empty
386	*/
387	E peek();
388
389	/**
390	* Retrieves, but does not remove, the head of the queue represented by
391	* this deque. This method differs from the <tt>peek</tt> method only in
392	* that it throws an exception if this deque is empty.
393	*
394	* <p>This method is equivalent to {@link #firstElement()}
395	*
396	* @return the head of the queue represented by this deque
397	* @throws NoSuchElementException if this deque is empty
398	*/
399	E element();
400
401
402	// * Stack methods *
403
404	/**
405	* Pushes an element onto the stack represented by this deque. In other
406	* words, inserts the element to the front this deque unless it would
407	* violate capacity restrictions.
408	*
409	* <p>This method is equivalent to {@link #addFirst}.
410	*
411	* @throws IllegalStateException if it was not possible to insert
412	* the element due to capacity restrictions
413	* @throws NullPointerException if <tt>e</tt> is null and this
414	* deque does not permit null elements
415	*/
416	void push(E e);
417
418	/**
419	* Pops an element from the stack represented by this deque. In other
420	* words, removes and returns the the first element of this deque.
421	*
422	* <p>This method is equivalent to {@link #removeFirst()}.
423	*
424	* @return the element at the front of this deque (which is the top
425	* of the stack represented by this deque)
426	* @throws NoSuchElementException if this deque is empty
427	*/
428	E pop();
429
430
431	// * Collection Method *
432
433	/**
434	* Returns an iterator over the elements in this deque. The elements
435	* will be ordered from first (head) to last (tail).
436	*
437	* @return an <tt>Iterator</tt> over the elements in this deque
438	*/
439	Iterator<E> iterator();
440	}