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>
 *   <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>
 *   <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();

    /**
     * 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>peekFirst</tt> method only
     * in that it throws an exception if this deque is empty.
     *
     * @return the first element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E getFirst();

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

    /**
     * Removes the first occurrence of the specified element in this
     * deque.  If the deque does not contain the element, it is
     * unchanged.  More formally, removes the first element <tt>e</tt>
     * such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
     * such an element exists).
     *
     * @param 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 <tt>poll</tt> method only in that it
     * throws an exception if this deque is empty.
     *
     * <p>This method is equivalent to {@link #removeFirst()}.
     *
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E remove();

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

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


    // *** Stack methods ***

    /**
     * Pushes an element onto the stack represented by this deque.  In other
     * words, inserts the element 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:	1.4
Committed:	Tue Mar 22 16:48:32 2005 UTC (19 years, 1 month ago) by dl
Branch:	MAIN
Changes since 1.3:	+8 -6 lines
Log Message:	Documentation improvements
#	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	dl	1.2	* following table:<p>
29	dl	1.3	*
30	dl	1.1	* <table BORDER CELLPADDING=3 CELLSPACING=1>
31			* <tr>
32			* <td></td>
33			* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
34			* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
35			* </tr>
36			* <tr>
37			* <td></td>
38			* <td ALIGN=CENTER><em>Throws exception</em></td>
39			* <td ALIGN=CENTER><em>Returns special value</em></td>
40			* <td ALIGN=CENTER><em>Throws exception</em></td>
41			* <td ALIGN=CENTER><em>Returns special value</em></td>
42			* </tr>
43			* <tr>
44			* <td><b>Insert</b></td>
45			* <td>{@link #addFirst addFirst(e)}</td>
46			* <td>{@link #offerFirst offerFirst(e)}</td>
47			* <td>{@link #addLast addLast(e)}</td>
48			* <td>{@link #offerLast offerLast(e)}</td>
49			* </tr>
50			* <tr>
51			* <td><b>Remove</b></td>
52			* <td>{@link #removeFirst removeFirst()}</td>
53			* <td>{@link #pollFirst pollFirst()}</td>
54			* <td>{@link #removeLast removeLast()}</td>
55			* <td>{@link #pollLast pollLast()}</td>
56			* </tr>
57			* <tr>
58			* <td><b>Examine</b></td>
59			* <td>{@link #getFirst getFirst()}</td>
60			* <td>{@link #peekFirst peekFirst()}</td>
61			* <td>{@link #getLast getLast()}</td>
62			* <td>{@link #peekLast peekLast()}</td>
63			* </tr>
64			* </table>
65			*
66			* <p>This interface extends the {@link Queue} interface. When a deque is
67			* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
68	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			* <tt>Deque</tt> methods as indicated in the following table:<p>
71			*
72			* <table BORDER CELLPADDING=3 CELLSPACING=1>
73			* <tr>
74			* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
75			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
76			* </tr>
77			* <tr>
78			* <tr>
79			* <td>{@link java.util.Queue#offer offer(e)}</td>
80			* <td>{@link #offerLast offerLast(e)}</td>
81			* </tr>
82			* <tr>
83			* <td>{@link java.util.Queue#add add(e)}</td>
84			* <td>{@link #addLast addLast(e)}</td>
85			* </tr>
86			* <tr>
87			* <td>{@link java.util.Queue#poll poll()}</td>
88			* <td>{@link #pollFirst pollFirst()}</td>
89			* </tr>
90			* <tr>
91			* <td>{@link java.util.Queue#remove remove()}</td>
92			* <td>{@link #removeFirst removeFirst()}</td>
93			* </tr>
94			* <tr>
95			* <td>{@link java.util.Queue#peek peek()}</td>
96			* <td>{@link #peek peekFirst()}</td>
97			* </tr>
98			* <tr>
99			* <td>{@link java.util.Queue#element element()}</td>
100			* <td>{@link #getFirst getFirst()}</td>
101			* </tr>
102			* </table>
103			*
104			* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
105			* interface should be used in preference to the legacy {@link Stack} class.
106	dl	1.3	* When a deque is used as a stack, elements are pushed and popped from the
107	dl	1.1	* beginning of the deque. Stack methods are precisely equivalent to
108			* <tt>Deque</tt> methods as indicated in the table below:<p>
109			*
110			* <table BORDER CELLPADDING=3 CELLSPACING=1>
111			* <tr>
112			* <td ALIGN=CENTER> <b>Stack Method</b></td>
113			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
114			* </tr>
115			* <tr>
116			* <tr>
117			* <td>{@link #push push(e)}</td>
118			* <td>{@link #addFirst addFirst(e)}</td>
119			* </tr>
120			* <tr>
121			* <td>{@link #pop pop()}</td>
122			* <td>{@link #removeFirst removeFirst()}</td>
123			* </tr>
124			* <tr>
125			* <td>{@link #peek peek()}</td>
126			* <td>{@link #peekFirst peekFirst()}</td>
127			* </tr>
128			* </table>
129			*
130			* <p>Note that the {@link #peek peek} method works equally well when
131			* a deque is used as a queue or a stack; in either case, elements are
132			* drawn from the beginning of the deque.
133			*
134	dl	1.2	* <p>This interface provides two methods to remove interior
135	dl	1.1	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
136			* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
137			* {@link List} interface, this interface does not provide support for
138			* indexed access to elements.
139			*
140			* <p>While <tt>Deque</tt> implementations are not strictly required
141			* to prohibit the insertion of null elements, they are strongly
142			* encouraged to do so. Users of any <tt>Deque</tt> implementations
143			* that do allow null elements are strongly encouraged <i>not</i> to
144			* take advantage of the ability to insert nulls. This is so because
145			* <tt>null</tt> is used as a special return value by various methods
146			* to indicated that the deque is empty.
147	dl	1.3	*
148	dl	1.1	* <p><tt>Deque</tt> implementations generally do not define
149			* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
150			* methods, but instead inherit the identity-based versions from class
151			* <tt>Object</tt>.
152			*
153			* <p>This interface is a member of the <a
154			* href="{@docRoot}/../guide/collections/index.html"> Java Collections
155			* Framework</a>.
156			*
157			* @author Doug Lea
158			* @author Josh Bloch
159			* @since 1.6
160			* @param <E> the type of elements held in this collection
161			*/
162
163			public interface Deque<E> extends Queue<E> {
164			/**
165	dl	1.3	* Inserts the specified element at the front of this deque unless it would
166	dl	1.1	* violate capacity restrictions. When using a capacity-restricted deque,
167			* this method is generally preferable to method <tt>addFirst</tt>, which
168			* can fail to insert an element only by throwing an exception.
169			*
170			* @param e the element to insert
171			* @return <tt>true</tt> if it was possible to insert the element,
172			* else <tt>false</tt>
173	dl	1.3	* @throws NullPointerException if the specified element is null and this
174	dl	1.1	* deque does not permit null elements
175			*/
176			boolean offerFirst(E e);
177
178			/**
179	dl	1.4	* Inserts the specified element at the end of this deque unless it would
180	dl	1.1	* violate capacity restrictions. When using a capacity-restricted deque,
181			* this method is generally preferable to method <tt>addLast</tt> which
182			* can fail to insert an element only by throwing an exception.
183			*
184			* @param e the element to insert
185			* @return <tt>true</tt> if it was possible to insert the element,
186			* else <tt>false</tt>
187	dl	1.3	* @throws NullPointerException if the specified element is null and this
188	dl	1.1	* deque does not permit null elements
189			*/
190			boolean offerLast(E e);
191
192			/**
193	dl	1.3	* Inserts the specified element at the front of this deque unless it
194	dl	1.1	* would violate capacity restrictions.
195			*
196			* @param e the element to insert
197			* @throws IllegalStateException if it was not possible to insert
198			* the element due to capacity restrictions
199	dl	1.3	* @throws NullPointerException if the specified element is null and this
200	dl	1.1	* deque does not permit null elements
201			*/
202			void addFirst(E e);
203
204			/**
205	dl	1.4	* Inserts the specified element at the end of this deque unless it would
206	dl	1.1	* violate capacity restrictions.
207			*
208			* @param e the element to insert
209			* @throws IllegalStateException if it was not possible to insert
210			* the element due to capacity restrictions
211	dl	1.3	* @throws NullPointerException if the specified element is null and this
212	dl	1.1	* deque does not permit null elements
213			*/
214			void addLast(E e);
215
216			/**
217			* Retrieves and removes the first element of this deque, or
218			* <tt>null</tt> if this deque is empty.
219			*
220			* @return the first element of this deque, or <tt>null</tt> if
221			* this deque is empty
222			*/
223			E pollFirst();
224
225			/**
226			* Retrieves and removes the last element of this deque, or
227			* <tt>null</tt> if this deque is empty.
228			*
229			* @return the last element of this deque, or <tt>null</tt> if
230			* this deque is empty
231			*/
232			E pollLast();
233
234			/**
235			* Removes and returns the first element of this deque. This method
236			* differs from the <tt>pollFirst</tt> method only in that it throws an
237			* exception if this deque is empty.
238			*
239			* @return the first element of this deque
240			* @throws NoSuchElementException if this deque is empty
241			*/
242			E removeFirst();
243
244			/**
245			* Retrieves and removes the last element of this deque. This method
246			* differs from the <tt>pollLast</tt> method only in that it throws an
247			* exception if this deque is empty.
248			*
249			* @return the last element of this deque
250			* @throws NoSuchElementException if this deque is empty
251			*/
252			E removeLast();
253
254			/**
255			* Retrieves, but does not remove, the first element of this deque,
256			* returning <tt>null</tt> if this deque is empty.
257			*
258			* @return the first element of this deque, or <tt>null</tt> if
259			* this deque is empty
260			*/
261			E peekFirst();
262
263			/**
264			* Retrieves, but does not remove, the last element of this deque,
265			* returning <tt>null</tt> if this deque is empty.
266			*
267			* @return the last element of this deque, or <tt>null</tt> if this deque
268			* is empty
269			*/
270			E peekLast();
271
272			/**
273			* Retrieves, but does not remove, the first element of this
274	dl	1.3	* deque. This method differs from the <tt>peekFirst</tt> method only
275	dl	1.1	* in that it throws an exception if this deque is empty.
276			*
277			* @return the first element of this deque
278			* @throws NoSuchElementException if this deque is empty
279			*/
280			E getFirst();
281
282			/**
283			* Retrieves, but does not remove, the last element of this
284	dl	1.3	* deque. This method differs from the <tt>peekLast</tt> method only
285	dl	1.1	* in that it throws an exception if this deque is empty.
286			*
287			* @return the last element of this deque
288			* @throws NoSuchElementException if this deque is empty
289			*/
290			E getLast();
291
292			/**
293			* Removes the first occurrence of the specified element in this
294			* deque. If the deque does not contain the element, it is
295			* unchanged. More formally, removes the first element <tt>e</tt>
296			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
297			* such an element exists).
298			*
299	dl	1.3	* @param o element to be removed from this deque, if present
300	dl	1.1	* @return <tt>true</tt> if the deque contained the specified element
301	dl	1.4	* @throws NullPointerException if the specified element is null and this
302			* deque does not permit null elements
303	dl	1.1	*/
304	dl	1.3	boolean removeFirstOccurrence(Object o);
305	dl	1.1
306			/**
307			* Removes the last occurrence of the specified element in this
308			* deque. If the deque does not contain the element, it is
309			* unchanged. More formally, removes the last element <tt>e</tt>
310			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
311			* such an element exists).
312			*
313	dl	1.3	* @param o element to be removed from this deque, if present
314	dl	1.1	* @return <tt>true</tt> if the deque contained the specified element
315	dl	1.4	* @throws NullPointerException if the specified element is null and this
316			* deque does not permit null elements
317	dl	1.1	*/
318	dl	1.3	boolean removeLastOccurrence(Object o);
319	dl	1.1
320
321			// * Queue methods *
322
323			/**
324			* Inserts the specified element into the queue represented by this deque
325			* unless it would violate capacity restrictions. In other words, inserts
326	dl	1.4	* the specified element at the end of this deque. When using a
327	dl	1.1	* capacity-restricted deque, this method is generally preferable to the
328			* {@link #add} method, which can fail to insert an element only by
329			* throwing an exception.
330			*
331			* <p>This method is equivalent to {@link #offerLast}.
332			*
333			* @param e the element to insert
334			* @return <tt>true</tt> if it was possible to insert the element,
335			* else <tt>false</tt>
336	dl	1.3	* @throws NullPointerException if the specified element is null and this
337	dl	1.1	* deque does not permit null elements
338			*/
339			boolean offer(E e);
340
341			/**
342			* Inserts the specified element into the queue represented by this
343			* deque unless it would violate capacity restrictions. In other words,
344	dl	1.3	* inserts the specified element as the last element of this deque.
345	dl	1.1	*
346			* <p>This method is equivalent to {@link #addLast}.
347			*
348			* @param e the element to insert
349			* @return <tt>true</tt> (as per the spec for {@link Collection#add})
350			* @throws IllegalStateException if it was not possible to insert
351			* the element due to capacity restrictions
352	dl	1.3	* @throws NullPointerException if the specified element is null and this
353	dl	1.1	* deque does not permit null elements
354			*/
355			boolean add(E e);
356
357			/**
358			* Retrieves and removes the head of the queue represented by
359			* this deque, or <tt>null</tt> if this deque is empty. In other words,
360			* retrieves and removes the first element of this deque, or <tt>null</tt>
361			* if this deque is empty.
362			*
363			* <p>This method is equivalent to {@link #pollFirst()}.
364			*
365			* @return the first element of this deque, or <tt>null</tt> if
366			* this deque is empty
367			*/
368			E poll();
369
370			/**
371			* Retrieves and removes the head of the queue represented by this deque.
372			* This method differs from the <tt>poll</tt> method only in that it
373			* throws an exception if this deque is empty.
374			*
375			* <p>This method is equivalent to {@link #removeFirst()}.
376			*
377			* @return the head of the queue represented by this deque
378			* @throws NoSuchElementException if this deque is empty
379			*/
380			E remove();
381
382			/**
383			* Retrieves, but does not remove, the head of the queue represented by
384			* this deque, returning <tt>null</tt> if this deque is empty.
385			*
386	dl	1.3	* <p>This method is equivalent to {@link #peekFirst()}.
387	dl	1.1	*
388			* @return the head of the queue represented by this deque, or
389			* <tt>null</tt> if this deque is empty
390			*/
391			E peek();
392
393			/**
394			* Retrieves, but does not remove, the head of the queue represented by
395			* this deque. This method differs from the <tt>peek</tt> method only in
396			* that it throws an exception if this deque is empty.
397			*
398	dl	1.3	* <p>This method is equivalent to {@link #getFirst()}.
399	dl	1.1	*
400			* @return the head of the queue represented by this deque
401			* @throws NoSuchElementException if this deque is empty
402			*/
403			E element();
404
405
406			// * Stack methods *
407
408			/**
409			* Pushes an element onto the stack represented by this deque. In other
410	dl	1.3	* words, inserts the element at the front of this deque unless it would
411	dl	1.1	* violate capacity restrictions.
412			*
413			* <p>This method is equivalent to {@link #addFirst}.
414			*
415	dl	1.3	* @param e the element to push
416	dl	1.1	* @throws IllegalStateException if it was not possible to insert
417			* the element due to capacity restrictions
418	dl	1.3	* @throws NullPointerException if the specified element is null and this
419	dl	1.1	* deque does not permit null elements
420			*/
421			void push(E e);
422
423			/**
424			* Pops an element from the stack represented by this deque. In other
425	dl	1.2	* words, removes and returns the first element of this deque.
426	dl	1.1	*
427			* <p>This method is equivalent to {@link #removeFirst()}.
428			*
429			* @return the element at the front of this deque (which is the top
430			* of the stack represented by this deque)
431			* @throws NoSuchElementException if this deque is empty
432			*/
433			E pop();
434
435
436			// * Collection Method *
437
438			/**
439			* Returns an iterator over the elements in this deque. The elements
440			* will be ordered from first (head) to last (tail).
441	dl	1.3	*
442	dl	1.1	* @return an <tt>Iterator</tt> over the elements in this deque
443			*/
444			Iterator<E> iterator();
445			}