java/util/Deque.java

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

package java.util;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


    // *** Queue methods ***

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

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

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

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

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

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


    // *** Stack methods ***

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

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


    // *** Collection Method ***

    /**
     * Returns an iterator over the elements in this deque.  The elements
     * will be ordered from first (head) to last (tail).
     *
     * @return an <tt>Iterator</tt> over the elements in this deque
     */
    Iterator<E> iterator();
}
Revision:	1.6
Committed:	Mon May 2 04:19:58 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.5:	+6 -6 lines
Log Message:	doc fixes
#	User	Rev	Content
1	dl	1.1	/*
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	dl	1.3	* <p>The twelve methods described above are summarized in the
28	jsr166	1.5	* following table:
29	dl	1.3	*
30	jsr166	1.5	* <p><table BORDER CELLPADDING=3 CELLSPACING=1>
31	dl	1.1	* <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	dl	1.4	* added at the end of the deque and removed from the beginning. The methods
69	dl	1.1	* inherited from the <tt>Queue</tt> interface are precisely equivalent to
70	jsr166	1.5	* <tt>Deque</tt> methods as indicated in the following table:
71	dl	1.1	*
72	jsr166	1.5	* <p><table BORDER CELLPADDING=3 CELLSPACING=1>
73	dl	1.1	* <tr>
74			* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
75			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
76			* </tr>
77			* <tr>
78			* <td>{@link java.util.Queue#offer offer(e)}</td>
79			* <td>{@link #offerLast offerLast(e)}</td>
80	jsr166	1.5	* </tr>
81			* <tr>
82	dl	1.1	* <td>{@link java.util.Queue#add add(e)}</td>
83			* <td>{@link #addLast addLast(e)}</td>
84	jsr166	1.5	* </tr>
85			* <tr>
86	dl	1.1	* <td>{@link java.util.Queue#poll poll()}</td>
87			* <td>{@link #pollFirst pollFirst()}</td>
88	jsr166	1.5	* </tr>
89			* <tr>
90	dl	1.1	* <td>{@link java.util.Queue#remove remove()}</td>
91			* <td>{@link #removeFirst removeFirst()}</td>
92	jsr166	1.5	* </tr>
93			* <tr>
94	dl	1.1	* <td>{@link java.util.Queue#peek peek()}</td>
95			* <td>{@link #peek peekFirst()}</td>
96	jsr166	1.5	* </tr>
97			* <tr>
98	dl	1.1	* <td>{@link java.util.Queue#element element()}</td>
99			* <td>{@link #getFirst getFirst()}</td>
100	jsr166	1.5	* </tr>
101	dl	1.1	* </table>
102			*
103			* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
104			* interface should be used in preference to the legacy {@link Stack} class.
105	dl	1.3	* When a deque is used as a stack, elements are pushed and popped from the
106	dl	1.1	* beginning of the deque. Stack methods are precisely equivalent to
107	jsr166	1.5	* <tt>Deque</tt> methods as indicated in the table below:
108	dl	1.1	*
109	jsr166	1.5	* <p><table BORDER CELLPADDING=3 CELLSPACING=1>
110	dl	1.1	* <tr>
111			* <td ALIGN=CENTER> <b>Stack Method</b></td>
112			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
113			* </tr>
114			* <tr>
115			* <td>{@link #push push(e)}</td>
116			* <td>{@link #addFirst addFirst(e)}</td>
117	jsr166	1.5	* </tr>
118			* <tr>
119	dl	1.1	* <td>{@link #pop pop()}</td>
120			* <td>{@link #removeFirst removeFirst()}</td>
121	jsr166	1.5	* </tr>
122			* <tr>
123	dl	1.1	* <td>{@link #peek peek()}</td>
124			* <td>{@link #peekFirst peekFirst()}</td>
125	jsr166	1.5	* </tr>
126	dl	1.1	* </table>
127			*
128			* <p>Note that the {@link #peek peek} method works equally well when
129			* a deque is used as a queue or a stack; in either case, elements are
130			* drawn from the beginning of the deque.
131			*
132	dl	1.2	* <p>This interface provides two methods to remove interior
133	dl	1.1	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
134			* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
135			* {@link List} interface, this interface does not provide support for
136			* indexed access to elements.
137			*
138			* <p>While <tt>Deque</tt> implementations are not strictly required
139			* to prohibit the insertion of null elements, they are strongly
140			* encouraged to do so. Users of any <tt>Deque</tt> implementations
141			* that do allow null elements are strongly encouraged <i>not</i> to
142			* take advantage of the ability to insert nulls. This is so because
143			* <tt>null</tt> is used as a special return value by various methods
144			* to indicated that the deque is empty.
145	dl	1.3	*
146	dl	1.1	* <p><tt>Deque</tt> implementations generally do not define
147			* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
148			* methods, but instead inherit the identity-based versions from class
149			* <tt>Object</tt>.
150			*
151			* <p>This interface is a member of the <a
152			* href="{@docRoot}/../guide/collections/index.html"> Java Collections
153			* Framework</a>.
154			*
155			* @author Doug Lea
156			* @author Josh Bloch
157			* @since 1.6
158			* @param <E> the type of elements held in this collection
159			*/
160
161			public interface Deque<E> extends Queue<E> {
162			/**
163	dl	1.3	* Inserts the specified element at the front of this deque unless it would
164	dl	1.1	* 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	dl	1.3	* @throws NullPointerException if the specified element is null and this
172	dl	1.1	* deque does not permit null elements
173			*/
174			boolean offerFirst(E e);
175
176			/**
177	dl	1.4	* Inserts the specified element at the end of this deque unless it would
178	dl	1.1	* 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	dl	1.3	* @throws NullPointerException if the specified element is null and this
186	dl	1.1	* deque does not permit null elements
187			*/
188			boolean offerLast(E e);
189
190			/**
191	dl	1.3	* Inserts the specified element at the front of this deque unless it
192	dl	1.1	* 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	dl	1.3	* @throws NullPointerException if the specified element is null and this
198	dl	1.1	* deque does not permit null elements
199			*/
200			void addFirst(E e);
201
202			/**
203	dl	1.4	* Inserts the specified element at the end of this deque unless it would
204	dl	1.1	* 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	dl	1.3	* @throws NullPointerException if the specified element is null and this
210	dl	1.1	* 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	jsr166	1.5	* Retrieves and removes the first element of this deque. This method
234	jsr166	1.6	* differs from the {@link #pollFirst} method only in that it throws an
235	dl	1.1	* 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	jsr166	1.6	* differs from the {@link #pollLast} method only in that it throws an
245	dl	1.1	* 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	jsr166	1.6	* deque. This method differs from the {@link #peekFirst} method only
273	dl	1.1	* in that it throws an exception if this deque is empty.
274			*
275			* @return the first element of this deque
276			* @throws NoSuchElementException if this deque is empty
277			*/
278			E getFirst();
279
280			/**
281			* Retrieves, but does not remove, the last element of this
282	jsr166	1.6	* deque. This method differs from the {@link #peekLast} method only
283	dl	1.1	* in that it throws an exception if this deque is empty.
284			*
285			* @return the last element of this deque
286			* @throws NoSuchElementException if this deque is empty
287			*/
288			E getLast();
289
290			/**
291			* Removes the first occurrence of the specified element in this
292			* deque. If the deque does not contain the element, it is
293			* unchanged. More formally, removes the first element <tt>e</tt>
294			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
295			* such an element exists).
296			*
297	dl	1.3	* @param o element to be removed from this deque, if present
298	dl	1.1	* @return <tt>true</tt> if the deque contained the specified element
299	dl	1.4	* @throws NullPointerException if the specified element is null and this
300			* deque does not permit null elements
301	dl	1.1	*/
302	dl	1.3	boolean removeFirstOccurrence(Object o);
303	dl	1.1
304			/**
305			* Removes the last occurrence of the specified element in this
306			* deque. If the deque does not contain the element, it is
307			* unchanged. More formally, removes the last element <tt>e</tt>
308			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
309			* such an element exists).
310			*
311	dl	1.3	* @param o element to be removed from this deque, if present
312	dl	1.1	* @return <tt>true</tt> if the deque contained the specified element
313	dl	1.4	* @throws NullPointerException if the specified element is null and this
314			* deque does not permit null elements
315	dl	1.1	*/
316	dl	1.3	boolean removeLastOccurrence(Object o);
317	dl	1.1
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	dl	1.4	* the specified element at the end of this deque. When using a
325	dl	1.1	* 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	dl	1.3	* @throws NullPointerException if the specified element is null and this
335	dl	1.1	* 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	dl	1.3	* inserts the specified element as the last element of this deque.
343	dl	1.1	*
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	dl	1.3	* @throws NullPointerException if the specified element is null and this
351	dl	1.1	* 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	jsr166	1.6	* This method differs from the {@link #poll} method only in that it
371	dl	1.1	* 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	dl	1.3	* <p>This method is equivalent to {@link #peekFirst()}.
385	dl	1.1	*
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	jsr166	1.6	* this deque. This method differs from the {@link #peek} method only in
394	dl	1.1	* that it throws an exception if this deque is empty.
395			*
396	dl	1.3	* <p>This method is equivalent to {@link #getFirst()}.
397	dl	1.1	*
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	dl	1.3	* words, inserts the element at the front of this deque unless it would
409	dl	1.1	* violate capacity restrictions.
410			*
411			* <p>This method is equivalent to {@link #addFirst}.
412			*
413	dl	1.3	* @param e the element to push
414	dl	1.1	* @throws IllegalStateException if it was not possible to insert
415			* the element due to capacity restrictions
416	dl	1.3	* @throws NullPointerException if the specified element is null and this
417	dl	1.1	* deque does not permit null elements
418			*/
419			void push(E e);
420
421			/**
422			* Pops an element from the stack represented by this deque. In other
423	dl	1.2	* words, removes and returns the first element of this deque.
424	dl	1.1	*
425			* <p>This method is equivalent to {@link #removeFirst()}.
426			*
427			* @return the element at the front of this deque (which is the top
428			* of the stack represented by this deque)
429			* @throws NoSuchElementException if this deque is empty
430			*/
431			E pop();
432
433
434			// * Collection Method *
435
436			/**
437			* Returns an iterator over the elements in this deque. The elements
438			* will be ordered from first (head) to last (tail).
439	dl	1.3	*
440	dl	1.1	* @return an <tt>Iterator</tt> over the elements in this deque
441			*/
442			Iterator<E> iterator();
443			}