java/util/Deque.java

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

package java.util;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


    // *** Queue methods ***

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

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

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

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

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

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


    // *** Stack methods ***

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

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


    // *** Collection Method ***

    /**
     * Returns an iterator over the elements in this deque.  The elements
     * will be ordered from first (head) to last (tail).
     *
     * @return an <tt>Iterator</tt> over the elements in this deque
     */
    Iterator<E> iterator();
}
Revision:	1.7
Committed:	Mon May 2 17:34:02 2005 UTC (19 years ago) by jsr166
Branch:	MAIN
Changes since 1.6:	+6 -3 lines
Log Message:	<p> before <table>
#	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	1.7	* <p>
31			* <table BORDER CELLPADDING=3 CELLSPACING=1>
32	dl	1.1	* <tr>
33			* <td></td>
34			* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
35			* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
36			* </tr>
37			* <tr>
38			* <td></td>
39			* <td ALIGN=CENTER><em>Throws exception</em></td>
40			* <td ALIGN=CENTER><em>Returns special value</em></td>
41			* <td ALIGN=CENTER><em>Throws exception</em></td>
42			* <td ALIGN=CENTER><em>Returns special value</em></td>
43			* </tr>
44			* <tr>
45			* <td><b>Insert</b></td>
46			* <td>{@link #addFirst addFirst(e)}</td>
47			* <td>{@link #offerFirst offerFirst(e)}</td>
48			* <td>{@link #addLast addLast(e)}</td>
49			* <td>{@link #offerLast offerLast(e)}</td>
50			* </tr>
51			* <tr>
52			* <td><b>Remove</b></td>
53			* <td>{@link #removeFirst removeFirst()}</td>
54			* <td>{@link #pollFirst pollFirst()}</td>
55			* <td>{@link #removeLast removeLast()}</td>
56			* <td>{@link #pollLast pollLast()}</td>
57			* </tr>
58			* <tr>
59			* <td><b>Examine</b></td>
60			* <td>{@link #getFirst getFirst()}</td>
61			* <td>{@link #peekFirst peekFirst()}</td>
62			* <td>{@link #getLast getLast()}</td>
63			* <td>{@link #peekLast peekLast()}</td>
64			* </tr>
65			* </table>
66			*
67			* <p>This interface extends the {@link Queue} interface. When a deque is
68			* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
69	dl	1.4	* added at the end of the deque and removed from the beginning. The methods
70	dl	1.1	* inherited from the <tt>Queue</tt> interface are precisely equivalent to
71	jsr166	1.5	* <tt>Deque</tt> methods as indicated in the following table:
72	dl	1.1	*
73	jsr166	1.7	* <p>
74			* <table BORDER CELLPADDING=3 CELLSPACING=1>
75	dl	1.1	* <tr>
76			* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
77			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
78			* </tr>
79			* <tr>
80			* <td>{@link java.util.Queue#offer offer(e)}</td>
81			* <td>{@link #offerLast offerLast(e)}</td>
82	jsr166	1.5	* </tr>
83			* <tr>
84	dl	1.1	* <td>{@link java.util.Queue#add add(e)}</td>
85			* <td>{@link #addLast addLast(e)}</td>
86	jsr166	1.5	* </tr>
87			* <tr>
88	dl	1.1	* <td>{@link java.util.Queue#poll poll()}</td>
89			* <td>{@link #pollFirst pollFirst()}</td>
90	jsr166	1.5	* </tr>
91			* <tr>
92	dl	1.1	* <td>{@link java.util.Queue#remove remove()}</td>
93			* <td>{@link #removeFirst removeFirst()}</td>
94	jsr166	1.5	* </tr>
95			* <tr>
96	dl	1.1	* <td>{@link java.util.Queue#peek peek()}</td>
97			* <td>{@link #peek peekFirst()}</td>
98	jsr166	1.5	* </tr>
99			* <tr>
100	dl	1.1	* <td>{@link java.util.Queue#element element()}</td>
101			* <td>{@link #getFirst getFirst()}</td>
102	jsr166	1.5	* </tr>
103	dl	1.1	* </table>
104			*
105			* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
106			* interface should be used in preference to the legacy {@link Stack} class.
107	dl	1.3	* When a deque is used as a stack, elements are pushed and popped from the
108	dl	1.1	* beginning of the deque. Stack methods are precisely equivalent to
109	jsr166	1.5	* <tt>Deque</tt> methods as indicated in the table below:
110	dl	1.1	*
111	jsr166	1.7	* <p>
112			* <table BORDER CELLPADDING=3 CELLSPACING=1>
113	dl	1.1	* <tr>
114			* <td ALIGN=CENTER> <b>Stack Method</b></td>
115			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
116			* </tr>
117			* <tr>
118			* <td>{@link #push push(e)}</td>
119			* <td>{@link #addFirst addFirst(e)}</td>
120	jsr166	1.5	* </tr>
121			* <tr>
122	dl	1.1	* <td>{@link #pop pop()}</td>
123			* <td>{@link #removeFirst removeFirst()}</td>
124	jsr166	1.5	* </tr>
125			* <tr>
126	dl	1.1	* <td>{@link #peek peek()}</td>
127			* <td>{@link #peekFirst peekFirst()}</td>
128	jsr166	1.5	* </tr>
129	dl	1.1	* </table>
130			*
131			* <p>Note that the {@link #peek peek} method works equally well when
132			* a deque is used as a queue or a stack; in either case, elements are
133			* drawn from the beginning of the deque.
134			*
135	dl	1.2	* <p>This interface provides two methods to remove interior
136	dl	1.1	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
137			* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
138			* {@link List} interface, this interface does not provide support for
139			* indexed access to elements.
140			*
141			* <p>While <tt>Deque</tt> implementations are not strictly required
142			* to prohibit the insertion of null elements, they are strongly
143			* encouraged to do so. Users of any <tt>Deque</tt> implementations
144			* that do allow null elements are strongly encouraged <i>not</i> to
145			* take advantage of the ability to insert nulls. This is so because
146			* <tt>null</tt> is used as a special return value by various methods
147			* to indicated that the deque is empty.
148	dl	1.3	*
149	dl	1.1	* <p><tt>Deque</tt> implementations generally do not define
150			* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
151			* methods, but instead inherit the identity-based versions from class
152			* <tt>Object</tt>.
153			*
154			* <p>This interface is a member of the <a
155			* href="{@docRoot}/../guide/collections/index.html"> Java Collections
156			* Framework</a>.
157			*
158			* @author Doug Lea
159			* @author Josh Bloch
160			* @since 1.6
161			* @param <E> the type of elements held in this collection
162			*/
163
164			public interface Deque<E> extends Queue<E> {
165			/**
166	dl	1.3	* Inserts the specified element at the front of this deque unless it would
167	dl	1.1	* violate capacity restrictions. When using a capacity-restricted deque,
168			* this method is generally preferable to method <tt>addFirst</tt>, which
169			* can fail to insert an element only by throwing an exception.
170			*
171			* @param e the element to insert
172			* @return <tt>true</tt> if it was possible to insert the element,
173			* else <tt>false</tt>
174	dl	1.3	* @throws NullPointerException if the specified element is null and this
175	dl	1.1	* deque does not permit null elements
176			*/
177			boolean offerFirst(E e);
178
179			/**
180	dl	1.4	* Inserts the specified element at the end of this deque unless it would
181	dl	1.1	* violate capacity restrictions. When using a capacity-restricted deque,
182			* this method is generally preferable to method <tt>addLast</tt> which
183			* can fail to insert an element only by throwing an exception.
184			*
185			* @param e the element to insert
186			* @return <tt>true</tt> if it was possible to insert the element,
187			* else <tt>false</tt>
188	dl	1.3	* @throws NullPointerException if the specified element is null and this
189	dl	1.1	* deque does not permit null elements
190			*/
191			boolean offerLast(E e);
192
193			/**
194	dl	1.3	* Inserts the specified element at the front of this deque unless it
195	dl	1.1	* would violate capacity restrictions.
196			*
197			* @param e the element to insert
198			* @throws IllegalStateException if it was not possible to insert
199			* the element due to capacity restrictions
200	dl	1.3	* @throws NullPointerException if the specified element is null and this
201	dl	1.1	* deque does not permit null elements
202			*/
203			void addFirst(E e);
204
205			/**
206	dl	1.4	* Inserts the specified element at the end of this deque unless it would
207	dl	1.1	* violate capacity restrictions.
208			*
209			* @param e the element to insert
210			* @throws IllegalStateException if it was not possible to insert
211			* the element due to capacity restrictions
212	dl	1.3	* @throws NullPointerException if the specified element is null and this
213	dl	1.1	* deque does not permit null elements
214			*/
215			void addLast(E e);
216
217			/**
218			* Retrieves and removes the first element of this deque, or
219			* <tt>null</tt> if this deque is empty.
220			*
221			* @return the first element of this deque, or <tt>null</tt> if
222			* this deque is empty
223			*/
224			E pollFirst();
225
226			/**
227			* Retrieves and removes the last element of this deque, or
228			* <tt>null</tt> if this deque is empty.
229			*
230			* @return the last element of this deque, or <tt>null</tt> if
231			* this deque is empty
232			*/
233			E pollLast();
234
235			/**
236	jsr166	1.5	* Retrieves and removes the first element of this deque. This method
237	jsr166	1.6	* differs from the {@link #pollFirst} method only in that it throws an
238	dl	1.1	* exception if this deque is empty.
239			*
240			* @return the first element of this deque
241			* @throws NoSuchElementException if this deque is empty
242			*/
243			E removeFirst();
244
245			/**
246			* Retrieves and removes the last element of this deque. This method
247	jsr166	1.6	* differs from the {@link #pollLast} method only in that it throws an
248	dl	1.1	* exception if this deque is empty.
249			*
250			* @return the last element of this deque
251			* @throws NoSuchElementException if this deque is empty
252			*/
253			E removeLast();
254
255			/**
256			* Retrieves, but does not remove, the first element of this deque,
257			* returning <tt>null</tt> if this deque is empty.
258			*
259			* @return the first element of this deque, or <tt>null</tt> if
260			* this deque is empty
261			*/
262			E peekFirst();
263
264			/**
265			* Retrieves, but does not remove, the last element of this deque,
266			* returning <tt>null</tt> if this deque is empty.
267			*
268			* @return the last element of this deque, or <tt>null</tt> if this deque
269			* is empty
270			*/
271			E peekLast();
272
273			/**
274			* Retrieves, but does not remove, the first element of this
275	jsr166	1.6	* deque. This method differs from the {@link #peekFirst} method only
276	dl	1.1	* in that it throws an exception if this deque is empty.
277			*
278			* @return the first element of this deque
279			* @throws NoSuchElementException if this deque is empty
280			*/
281			E getFirst();
282
283			/**
284			* Retrieves, but does not remove, the last element of this
285	jsr166	1.6	* deque. This method differs from the {@link #peekLast} method only
286	dl	1.1	* in that it throws an exception if this deque is empty.
287			*
288			* @return the last element of this deque
289			* @throws NoSuchElementException if this deque is empty
290			*/
291			E getLast();
292
293			/**
294			* Removes the first occurrence of the specified element in this
295			* deque. If the deque does not contain the element, it is
296			* unchanged. More formally, removes the first element <tt>e</tt>
297			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
298			* such an element exists).
299			*
300	dl	1.3	* @param o element to be removed from this deque, if present
301	dl	1.1	* @return <tt>true</tt> if the deque contained the specified element
302	dl	1.4	* @throws NullPointerException if the specified element is null and this
303			* deque does not permit null elements
304	dl	1.1	*/
305	dl	1.3	boolean removeFirstOccurrence(Object o);
306	dl	1.1
307			/**
308			* Removes the last occurrence of the specified element in this
309			* deque. If the deque does not contain the element, it is
310			* unchanged. More formally, removes the last element <tt>e</tt>
311			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
312			* such an element exists).
313			*
314	dl	1.3	* @param o element to be removed from this deque, if present
315	dl	1.1	* @return <tt>true</tt> if the deque contained the specified element
316	dl	1.4	* @throws NullPointerException if the specified element is null and this
317			* deque does not permit null elements
318	dl	1.1	*/
319	dl	1.3	boolean removeLastOccurrence(Object o);
320	dl	1.1
321
322			// * Queue methods *
323
324			/**
325			* Inserts the specified element into the queue represented by this deque
326			* unless it would violate capacity restrictions. In other words, inserts
327	dl	1.4	* the specified element at the end of this deque. When using a
328	dl	1.1	* capacity-restricted deque, this method is generally preferable to the
329			* {@link #add} method, which can fail to insert an element only by
330			* throwing an exception.
331			*
332			* <p>This method is equivalent to {@link #offerLast}.
333			*
334			* @param e the element to insert
335			* @return <tt>true</tt> if it was possible to insert the element,
336			* else <tt>false</tt>
337	dl	1.3	* @throws NullPointerException if the specified element is null and this
338	dl	1.1	* deque does not permit null elements
339			*/
340			boolean offer(E e);
341
342			/**
343			* Inserts the specified element into the queue represented by this
344			* deque unless it would violate capacity restrictions. In other words,
345	dl	1.3	* inserts the specified element as the last element of this deque.
346	dl	1.1	*
347			* <p>This method is equivalent to {@link #addLast}.
348			*
349			* @param e the element to insert
350			* @return <tt>true</tt> (as per the spec for {@link Collection#add})
351			* @throws IllegalStateException if it was not possible to insert
352			* the element due to capacity restrictions
353	dl	1.3	* @throws NullPointerException if the specified element is null and this
354	dl	1.1	* deque does not permit null elements
355			*/
356			boolean add(E e);
357
358			/**
359			* Retrieves and removes the head of the queue represented by
360			* this deque, or <tt>null</tt> if this deque is empty. In other words,
361			* retrieves and removes the first element of this deque, or <tt>null</tt>
362			* if this deque is empty.
363			*
364			* <p>This method is equivalent to {@link #pollFirst()}.
365			*
366			* @return the first element of this deque, or <tt>null</tt> if
367			* this deque is empty
368			*/
369			E poll();
370
371			/**
372			* Retrieves and removes the head of the queue represented by this deque.
373	jsr166	1.6	* This method differs from the {@link #poll} method only in that it
374	dl	1.1	* throws an exception if this deque is empty.
375			*
376			* <p>This method is equivalent to {@link #removeFirst()}.
377			*
378			* @return the head of the queue represented by this deque
379			* @throws NoSuchElementException if this deque is empty
380			*/
381			E remove();
382
383			/**
384			* Retrieves, but does not remove, the head of the queue represented by
385			* this deque, returning <tt>null</tt> if this deque is empty.
386			*
387	dl	1.3	* <p>This method is equivalent to {@link #peekFirst()}.
388	dl	1.1	*
389			* @return the head of the queue represented by this deque, or
390			* <tt>null</tt> if this deque is empty
391			*/
392			E peek();
393
394			/**
395			* Retrieves, but does not remove, the head of the queue represented by
396	jsr166	1.6	* this deque. This method differs from the {@link #peek} method only in
397	dl	1.1	* that it throws an exception if this deque is empty.
398			*
399	dl	1.3	* <p>This method is equivalent to {@link #getFirst()}.
400	dl	1.1	*
401			* @return the head of the queue represented by this deque
402			* @throws NoSuchElementException if this deque is empty
403			*/
404			E element();
405
406
407			// * Stack methods *
408
409			/**
410			* Pushes an element onto the stack represented by this deque. In other
411	dl	1.3	* words, inserts the element at the front of this deque unless it would
412	dl	1.1	* violate capacity restrictions.
413			*
414			* <p>This method is equivalent to {@link #addFirst}.
415			*
416	dl	1.3	* @param e the element to push
417	dl	1.1	* @throws IllegalStateException if it was not possible to insert
418			* the element due to capacity restrictions
419	dl	1.3	* @throws NullPointerException if the specified element is null and this
420	dl	1.1	* deque does not permit null elements
421			*/
422			void push(E e);
423
424			/**
425			* Pops an element from the stack represented by this deque. In other
426	dl	1.2	* words, removes and returns the first element of this deque.
427	dl	1.1	*
428			* <p>This method is equivalent to {@link #removeFirst()}.
429			*
430			* @return the element at the front of this deque (which is the top
431			* of the stack represented by this deque)
432			* @throws NoSuchElementException if this deque is empty
433			*/
434			E pop();
435
436
437			// * Collection Method *
438
439			/**
440			* Returns an iterator over the elements in this deque. The elements
441			* will be ordered from first (head) to last (tail).
442	dl	1.3	*
443	dl	1.1	* @return an <tt>Iterator</tt> over the elements in this deque
444			*/
445			Iterator<E> iterator();
446			}