src/jsr166x/Deque.java

/*
 * Written by Doug Lea and Josh Bloch with assistance from members of
 * JCP JSR-166 Expert Group and released to the public domain, as explained
 * at http://creativecommons.org/publicdomain/zero/1.0/
 */

package jsr166x;     // XXX This belongs in java.util!!! XXX

import java.util.*;    // XXX This import goes away        XXX

/**
 * A linear collection that supports element insertion and removal at
 * both ends.  The name <i>deque</i> is short for "double ended queue"
 * and is usually pronounced "deck".  Most {@code Deque}
 * 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 {@code null} or {@code false}, depending on
 * the operation).  The latter form of the insert operation is
 * designed specifically for use with capacity-restricted
 * {@code Deque} implementations; in most implementations, insert
 * operations cannot fail.
 *
 * <p>The twelve methods described above are summarized in the
 * following table:<p>
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td></td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
 *  </tr>
 *  <tr>
 *    <td></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Returns special value</em></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Returns special value</em></td>
 *  </tr>
 *  <tr>
 *    <td><b>Insert</b></td>
 *    <td>{@link #addFirst addFirst(e)}</td>
 *    <td>{@link #offerFirst offerFirst(e)}</td>
 *    <td>{@link #addLast addLast(e)}</td>
 *    <td>{@link #offerLast offerLast(e)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Remove</b></td>
 *    <td>{@link #removeFirst removeFirst()}</td>
 *    <td>{@link #pollFirst pollFirst()}</td>
 *    <td>{@link #removeLast removeLast()}</td>
 *    <td>{@link #pollLast pollLast()}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Examine</b></td>
 *    <td>{@link #getFirst getFirst()}</td>
 *    <td>{@link #peekFirst peekFirst()}</td>
 *    <td>{@link #getLast getLast()}</td>
 *    <td>{@link #peekLast peekLast()}</td>
 *  </tr>
 * </table>
 *
 * <p>This interface extends the {@link Queue} interface.  When a deque is
 * used as a queue, FIFO (First-In-First-Out) behavior results.  Elements are
 * added to the end of the deque and removed from the beginning.  The methods
 * inherited from the {@code Queue} interface are precisely equivalent to
 * {@code Deque} methods as indicated in the following table:<p>
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 *  <tr>
 *    <td ALIGN=CENTER> <b>{@code Queue} Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
 *  </tr>
 *  <tr>
 *   <tr>
 *    <td>{@link java.util.Queue#offer offer(e)}</td>
 *    <td>{@link #offerLast offerLast(e)}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#add add(e)}</td>
 *    <td>{@link #addLast addLast(e)}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#poll poll()}</td>
 *    <td>{@link #pollFirst pollFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#remove remove()}</td>
 *    <td>{@link #removeFirst removeFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#peek peek()}</td>
 *    <td>{@link #peek peekFirst()}</td>
 *   </tr>
 *   <tr>
 *    <td>{@link java.util.Queue#element element()}</td>
 *    <td>{@link #getFirst getFirst()}</td>
 *   </tr>
 * </table>
 *
 * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks.  This
 * interface should be used in preference to the legacy {@link Stack} class.
 * When a dequeue is used as a stack, elements are pushed and popped from the
 * beginning of the deque.  Stack methods are precisely equivalent to
 * {@code Deque} 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 {@code Deque} 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 {@code Deque} implementations are not strictly required
 * to prohibit the insertion of null elements, they are strongly
 * encouraged to do so.  Users of any {@code Deque} 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
 * {@code null} is used as a special return value by various methods
 * to indicated that the deque is empty.
 *
 * <p>{@code Deque} implementations generally do not define
 * element-based versions of the {@code equals} and {@code hashCode}
 * methods, but instead inherit the identity-based versions from class
 * {@code Object}.
 *
 * <p>This interface is a member of the <a
 * href="{@docRoot}/../guide/collections/index.html"> Java Collections
 * Framework</a>.
 *
 * @author Doug Lea
 * @author Josh Bloch
 * @since  1.6
 * @param <E> the type of elements held in this collection
 */
public interface Deque<E> extends Queue<E> {
    /**
     * Inserts the specified element to the front this deque unless it would
     * violate capacity restrictions.  When using a capacity-restricted deque,
     * this method is generally preferable to method {@code addFirst}, which
     * can fail to insert an element only by throwing an exception.
     *
     * @param e the element to insert
     * @return {@code true} if it was possible to insert the element,
     *     else {@code false}
     * @throws NullPointerException if {@code e} is null and this
     *     deque does not permit null elements
     */
    boolean offerFirst(E e);

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

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

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

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

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

    /**
     * Removes and returns the first element of this deque.  This method
     * differs from the {@code 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 {@code 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 {@code null} if this deque is empty.
     *
     * @return the first element of this deque, or {@code null} if
     *     this deque is empty
     */
    E peekFirst();

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

    /**
     * Retrieves, but does not remove, the first element of this
     * deque.  This method differs from the {@code peek} 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 {@code peek} 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 {@code e}
     * such that {@code (o==null ? e==null : o.equals(e))} (if
     * such an element exists).
     *
     * @param e element to be removed from this deque, if present
     * @return {@code true} if the deque contained the specified element
     * @throws NullPointerException if the specified element is {@code null}
     */
    boolean removeFirstOccurrence(Object e);

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


    // *** Queue methods ***

    /**
     * Inserts the specified element into the queue represented by this deque
     * unless it would violate capacity restrictions.  In other words, inserts
     * the specified element to the end of this deque.  When using a
     * capacity-restricted deque, this method is generally preferable to the
     * {@link #add} method, which can fail to insert an element only by
     * throwing an exception.
     *
     * <p>This method is equivalent to {@link #offerLast}.
     *
     * @param e the element to insert
     * @return {@code true} if it was possible to insert the element,
     *     else {@code false}
     * @throws NullPointerException if {@code e} 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 {@code true} (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 {@code e} 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 {@code null} if this deque is empty.  In other words,
     * retrieves and removes the first element of this deque, or {@code null}
     * if this deque is empty.
     *
     * <p>This method is equivalent to {@link #pollFirst()}.
     *
     * @return the first element of this deque, or {@code null} if
     *     this deque is empty
     */
    E poll();

    /**
     * Retrieves and removes the head of the queue represented by this deque.
     * This method differs from the {@code 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 {@code null} if this deque is empty.
     *
     * <p>This method is equivalent to {@link #peekFirst()}.
     *
     * @return the head of the queue represented by this deque, or
     *     {@code null} 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 {@code 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 to the front this deque unless it would
     * violate capacity restrictions.
     *
     * <p>This method is equivalent to {@link #addFirst}.
     *
     * @throws IllegalStateException if it was not possible to insert
     *    the element due to capacity restrictions
     * @throws NullPointerException if {@code e} 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 {@code Iterator} over the elements in this deque
     */
    Iterator<E> iterator();
}
Revision:	1.13
Committed:	Sun Jan 18 20:17:33 2015 UTC (9 years, 3 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.12:	+1 -0 lines
Log Message:	exactly one blank line before and after package statements
#	User	Rev	Content
1	dl	1.1	/*
2	dl	1.3	* 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	jsr166	1.10	* at http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7	dl	1.3	package jsr166x; // XXX This belongs in java.util!!! XXX
8	jsr166	1.13
9	dl	1.3	import java.util.*; // XXX This import goes away XXX
10	dl	1.1
11			/**
12	dl	1.5	* A linear collection that supports element insertion and removal at
13			* both ends. The name <i>deque</i> is short for "double ended queue"
14	jsr166	1.11	* and is usually pronounced "deck". Most {@code Deque}
15	dl	1.3	* implementations place no fixed limits on the number of elements
16			* they may contain, but this interface supports capacity-restricted
17			* deques as well as those with no fixed size limit.
18			*
19	dl	1.5	* <p>This interface defines methods to access the elements at both
20			* ends of the deque. Methods are provided to insert, remove, and
21			* examine the element. Each of these methods exists in two forms:
22			* one throws an exception if the operation fails, the other returns a
23	jsr166	1.11	* special value (either {@code null} or {@code false}, depending on
24	dl	1.5	* the operation). The latter form of the insert operation is
25			* designed specifically for use with capacity-restricted
26	jsr166	1.11	* {@code Deque} implementations; in most implementations, insert
27	dl	1.5	* operations cannot fail.
28	dl	1.3	*
29	jsr166	1.9	* <p>The twelve methods described above are summarized in the
30			* following table:<p>
31	jsr166	1.6	*
32	dl	1.3	* <table BORDER CELLPADDING=3 CELLSPACING=1>
33			* <tr>
34			* <td></td>
35			* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
36			* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
37			* </tr>
38			* <tr>
39			* <td></td>
40			* <td ALIGN=CENTER><em>Throws exception</em></td>
41			* <td ALIGN=CENTER><em>Returns special value</em></td>
42			* <td ALIGN=CENTER><em>Throws exception</em></td>
43			* <td ALIGN=CENTER><em>Returns special value</em></td>
44			* </tr>
45			* <tr>
46			* <td><b>Insert</b></td>
47			* <td>{@link #addFirst addFirst(e)}</td>
48			* <td>{@link #offerFirst offerFirst(e)}</td>
49			* <td>{@link #addLast addLast(e)}</td>
50			* <td>{@link #offerLast offerLast(e)}</td>
51			* </tr>
52			* <tr>
53			* <td><b>Remove</b></td>
54			* <td>{@link #removeFirst removeFirst()}</td>
55			* <td>{@link #pollFirst pollFirst()}</td>
56			* <td>{@link #removeLast removeLast()}</td>
57			* <td>{@link #pollLast pollLast()}</td>
58			* </tr>
59			* <tr>
60			* <td><b>Examine</b></td>
61	dl	1.4	* <td>{@link #getFirst getFirst()}</td>
62	dl	1.3	* <td>{@link #peekFirst peekFirst()}</td>
63	dl	1.4	* <td>{@link #getLast getLast()}</td>
64	dl	1.3	* <td>{@link #peekLast peekLast()}</td>
65			* </tr>
66			* </table>
67			*
68			* <p>This interface extends the {@link Queue} interface. When a deque is
69			* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
70			* added to the end of the deque and removed from the beginning. The methods
71	jsr166	1.11	* inherited from the {@code Queue} interface are precisely equivalent to
72			* {@code Deque} methods as indicated in the following table:<p>
73	dl	1.3	*
74			* <table BORDER CELLPADDING=3 CELLSPACING=1>
75			* <tr>
76	jsr166	1.11	* <td ALIGN=CENTER> <b>{@code Queue} Method</b></td>
77			* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
78	dl	1.3	* </tr>
79			* <tr>
80			* <tr>
81			* <td>{@link java.util.Queue#offer offer(e)}</td>
82			* <td>{@link #offerLast offerLast(e)}</td>
83			* </tr>
84			* <tr>
85			* <td>{@link java.util.Queue#add add(e)}</td>
86			* <td>{@link #addLast addLast(e)}</td>
87			* </tr>
88			* <tr>
89			* <td>{@link java.util.Queue#poll poll()}</td>
90			* <td>{@link #pollFirst pollFirst()}</td>
91			* </tr>
92			* <tr>
93			* <td>{@link java.util.Queue#remove remove()}</td>
94			* <td>{@link #removeFirst removeFirst()}</td>
95			* </tr>
96			* <tr>
97			* <td>{@link java.util.Queue#peek peek()}</td>
98			* <td>{@link #peek peekFirst()}</td>
99			* </tr>
100			* <tr>
101			* <td>{@link java.util.Queue#element element()}</td>
102	dl	1.4	* <td>{@link #getFirst getFirst()}</td>
103	dl	1.3	* </tr>
104			* </table>
105			*
106			* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
107			* interface should be used in preference to the legacy {@link Stack} class.
108			* When a dequeue is used as a stack, elements are pushed and popped from the
109			* beginning of the deque. Stack methods are precisely equivalent to
110	jsr166	1.11	* {@code Deque} methods as indicated in the table below:<p>
111	dl	1.3	*
112			* <table BORDER CELLPADDING=3 CELLSPACING=1>
113			* <tr>
114			* <td ALIGN=CENTER> <b>Stack Method</b></td>
115	jsr166	1.11	* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td>
116	dl	1.3	* </tr>
117			* <tr>
118			* <tr>
119			* <td>{@link #push push(e)}</td>
120			* <td>{@link #addFirst addFirst(e)}</td>
121			* </tr>
122			* <tr>
123			* <td>{@link #pop pop()}</td>
124			* <td>{@link #removeFirst removeFirst()}</td>
125			* </tr>
126			* <tr>
127			* <td>{@link #peek peek()}</td>
128			* <td>{@link #peekFirst peekFirst()}</td>
129			* </tr>
130			* </table>
131	dl	1.5	*
132			* <p>Note that the {@link #peek peek} method works equally well when
133			* a deque is used as a queue or a stack; in either case, elements are
134			* drawn from the beginning of the deque.
135			*
136	jsr166	1.8	* <p>This interface provides two methods to remove interior
137	dl	1.5	* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
138			* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the
139			* {@link List} interface, this interface does not provide support for
140			* indexed access to elements.
141			*
142	jsr166	1.11	* <p>While {@code Deque} implementations are not strictly required
143	dl	1.5	* to prohibit the insertion of null elements, they are strongly
144	jsr166	1.11	* encouraged to do so. Users of any {@code Deque} implementations
145	dl	1.5	* that do allow null elements are strongly encouraged <i>not</i> to
146			* take advantage of the ability to insert nulls. This is so because
147	jsr166	1.11	* {@code null} is used as a special return value by various methods
148	dl	1.5	* to indicated that the deque is empty.
149	jsr166	1.6	*
150	jsr166	1.11	* <p>{@code Deque} implementations generally do not define
151			* element-based versions of the {@code equals} and {@code hashCode}
152	dl	1.3	* methods, but instead inherit the identity-based versions from class
153	jsr166	1.11	* {@code Object}.
154	dl	1.1	*
155			* <p>This interface is a member of the <a
156			* href="{@docRoot}/../guide/collections/index.html"> Java Collections
157			* Framework</a>.
158			*
159			* @author Doug Lea
160	dl	1.3	* @author Josh Bloch
161			* @since 1.6
162	dl	1.1	* @param <E> the type of elements held in this collection
163			*/
164	dl	1.3	public interface Deque<E> extends Queue<E> {
165	dl	1.1	/**
166	dl	1.3	* Inserts the specified element to the front this deque unless it would
167			* violate capacity restrictions. When using a capacity-restricted deque,
168	jsr166	1.11	* this method is generally preferable to method {@code addFirst}, which
169	dl	1.3	* can fail to insert an element only by throwing an exception.
170	dl	1.1	*
171	dl	1.3	* @param e the element to insert
172	jsr166	1.11	* @return {@code true} if it was possible to insert the element,
173			* else {@code false}
174			* @throws NullPointerException if {@code e} is null and this
175	dl	1.3	* deque does not permit null elements
176	dl	1.1	*/
177	dl	1.3	boolean offerFirst(E e);
178	dl	1.1
179			/**
180	dl	1.3	* Inserts the specified element to the end of this deque unless it would
181			* violate capacity restrictions. When using a capacity-restricted deque,
182	jsr166	1.11	* this method is generally preferable to method {@code addLast} which
183	dl	1.3	* can fail to insert an element only by throwing an exception.
184	dl	1.1	*
185	dl	1.3	* @param e the element to insert
186	jsr166	1.11	* @return {@code true} if it was possible to insert the element,
187			* else {@code false}
188			* @throws NullPointerException if {@code e} is null and this
189	dl	1.3	* deque does not permit null elements
190	dl	1.1	*/
191	dl	1.3	boolean offerLast(E e);
192	dl	1.1
193			/**
194	dl	1.3	* Inserts the specified element to the front of this deque unless it
195			* would violate capacity restrictions.
196	dl	1.1	*
197	dl	1.3	* @param e the element to insert
198			* @throws IllegalStateException if it was not possible to insert
199			* the element due to capacity restrictions
200	jsr166	1.11	* @throws NullPointerException if {@code e} is null and this
201	dl	1.3	* deque does not permit null elements
202	dl	1.1	*/
203	dl	1.3	void addFirst(E e);
204	dl	1.1
205			/**
206	dl	1.3	* Inserts the specified element to the end of this deque unless it would
207			* violate capacity restrictions.
208	dl	1.1	*
209	dl	1.3	* @param e the element to insert
210			* @throws IllegalStateException if it was not possible to insert
211			* the element due to capacity restrictions
212	jsr166	1.11	* @throws NullPointerException if {@code e} is null and this
213	dl	1.3	* deque does not permit null elements
214	dl	1.1	*/
215	dl	1.3	void addLast(E e);
216	dl	1.1
217			/**
218			* Retrieves and removes the first element of this deque, or
219	jsr166	1.11	* {@code null} if this deque is empty.
220	dl	1.1	*
221	jsr166	1.11	* @return the first element of this deque, or {@code null} if
222	dl	1.3	* this deque is empty
223	dl	1.1	*/
224			E pollFirst();
225
226			/**
227			* Retrieves and removes the last element of this deque, or
228	jsr166	1.11	* {@code null} if this deque is empty.
229	dl	1.1	*
230	jsr166	1.11	* @return the last element of this deque, or {@code null} if
231	dl	1.3	* this deque is empty
232	dl	1.1	*/
233			E pollLast();
234
235			/**
236	dl	1.3	* Removes and returns the first element of this deque. This method
237	jsr166	1.11	* differs from the {@code pollFirst} method only in that it throws an
238	dl	1.1	* exception if this deque is empty.
239			*
240	dl	1.3	* @return the first element of this deque
241			* @throws NoSuchElementException if this deque is empty
242	dl	1.1	*/
243			E removeFirst();
244
245			/**
246			* Retrieves and removes the last element of this deque. This method
247	jsr166	1.11	* differs from the {@code pollLast} method only in that it throws an
248	dl	1.1	* exception if this deque is empty.
249			*
250	dl	1.3	* @return the last element of this deque
251			* @throws NoSuchElementException if this deque is empty
252	dl	1.1	*/
253			E removeLast();
254
255			/**
256			* Retrieves, but does not remove, the first element of this deque,
257	jsr166	1.11	* returning {@code null} if this deque is empty.
258	dl	1.1	*
259	jsr166	1.11	* @return the first element of this deque, or {@code null} if
260	dl	1.3	* this deque is empty
261	dl	1.1	*/
262			E peekFirst();
263
264			/**
265			* Retrieves, but does not remove, the last element of this deque,
266	jsr166	1.11	* returning {@code null} if this deque is empty.
267	dl	1.1	*
268	jsr166	1.11	* @return the last element of this deque, or {@code null} if this deque
269	dl	1.3	* is empty
270	dl	1.1	*/
271			E peekLast();
272
273			/**
274			* Retrieves, but does not remove, the first element of this
275	jsr166	1.11	* deque. This method differs from the {@code peek} method only
276	dl	1.1	* in that it throws an exception if this deque is empty.
277			*
278	dl	1.3	* @return the first element of this deque
279			* @throws NoSuchElementException if this deque is empty
280	dl	1.1	*/
281	dl	1.4	E getFirst();
282	dl	1.1
283			/**
284			* Retrieves, but does not remove, the last element of this
285	jsr166	1.11	* deque. This method differs from the {@code peek} method only
286	dl	1.1	* in that it throws an exception if this deque is empty.
287			*
288	dl	1.3	* @return the last element of this deque
289			* @throws NoSuchElementException if this deque is empty
290	dl	1.1	*/
291	dl	1.4	E getLast();
292	dl	1.1
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	jsr166	1.11	* unchanged. More formally, removes the first element {@code e}
297			* such that {@code (o==null ? e==null : o.equals(e))} (if
298	dl	1.1	* such an element exists).
299			*
300	dl	1.3	* @param e element to be removed from this deque, if present
301	jsr166	1.11	* @return {@code true} if the deque contained the specified element
302			* @throws NullPointerException if the specified element is {@code null}
303	dl	1.1	*/
304	dl	1.3	boolean removeFirstOccurrence(Object e);
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	jsr166	1.11	* unchanged. More formally, removes the last element {@code e}
310			* such that {@code (o==null ? e==null : o.equals(e))} (if
311	dl	1.1	* such an element exists).
312			*
313	dl	1.3	* @param e element to be removed from this deque, if present
314	jsr166	1.11	* @return {@code true} if the deque contained the specified element
315			* @throws NullPointerException if the specified element is {@code null}
316	dl	1.1	*/
317	dl	1.3	boolean removeLastOccurrence(Object e);
318
319
320			// * Queue methods *
321	dl	1.1
322			/**
323	dl	1.3	* Inserts the specified element into the queue represented by this deque
324			* unless it would violate capacity restrictions. In other words, inserts
325			* the specified element to the end of this deque. When using a
326			* capacity-restricted deque, this method is generally preferable to the
327			* {@link #add} method, which can fail to insert an element only by
328			* throwing an exception.
329			*
330			* <p>This method is equivalent to {@link #offerLast}.
331			*
332			* @param e the element to insert
333	jsr166	1.11	* @return {@code true} if it was possible to insert the element,
334			* else {@code false}
335			* @throws NullPointerException if {@code e} is null and this
336	dl	1.3	* deque does not permit null elements
337	dl	1.1	*/
338	dl	1.3	boolean offer(E e);
339	dl	1.1
340			/**
341	dl	1.3	* Inserts the specified element into the queue represented by this
342			* deque unless it would violate capacity restrictions. In other words,
343	jsr166	1.6	* inserts the specified element as the last element of this deque.
344	dl	1.3	*
345			* <p>This method is equivalent to {@link #addLast}.
346			*
347			* @param e the element to insert
348	jsr166	1.11	* @return {@code true} (as per the spec for {@link Collection#add})
349	dl	1.3	* @throws IllegalStateException if it was not possible to insert
350			* the element due to capacity restrictions
351	jsr166	1.11	* @throws NullPointerException if {@code e} is null and this
352	dl	1.3	* deque does not permit null elements
353			*/
354			boolean add(E e);
355
356			/**
357			* Retrieves and removes the head of the queue represented by
358	jsr166	1.11	* this deque, or {@code null} if this deque is empty. In other words,
359			* retrieves and removes the first element of this deque, or {@code null}
360	dl	1.3	* if this deque is empty.
361			*
362			* <p>This method is equivalent to {@link #pollFirst()}.
363			*
364	jsr166	1.11	* @return the first element of this deque, or {@code null} if
365	dl	1.3	* this deque is empty
366			*/
367			E poll();
368
369			/**
370			* Retrieves and removes the head of the queue represented by this deque.
371	jsr166	1.11	* This method differs from the {@code poll} method only in that it
372	dl	1.3	* throws an exception if this deque is empty.
373			*
374			* <p>This method is equivalent to {@link #removeFirst()}.
375			*
376			* @return the head of the queue represented by this deque
377			* @throws NoSuchElementException if this deque is empty
378	dl	1.1	*/
379	dl	1.3	E remove();
380	dl	1.1
381	dl	1.3	/**
382			* Retrieves, but does not remove, the head of the queue represented by
383	jsr166	1.11	* this deque, returning {@code null} if this deque is empty.
384	dl	1.3	*
385	jsr166	1.12	* <p>This method is equivalent to {@link #peekFirst()}.
386	dl	1.3	*
387			* @return the head of the queue represented by this deque, or
388	jsr166	1.11	* {@code null} if this deque is empty
389	dl	1.3	*/
390			E peek();
391
392			/**
393			* Retrieves, but does not remove, the head of the queue represented by
394	jsr166	1.11	* this deque. This method differs from the {@code peek} method only in
395	dl	1.3	* that it throws an exception if this deque is empty.
396			*
397	jsr166	1.12	* <p>This method is equivalent to {@link #getFirst()}.
398	dl	1.3	*
399			* @return the head of the queue represented by this deque
400			* @throws NoSuchElementException if this deque is empty
401			*/
402			E element();
403
404
405			// * Stack methods *
406
407			/**
408			* Pushes an element onto the stack represented by this deque. In other
409			* words, inserts the element to the front this deque unless it would
410			* violate capacity restrictions.
411			*
412			* <p>This method is equivalent to {@link #addFirst}.
413			*
414			* @throws IllegalStateException if it was not possible to insert
415			* the element due to capacity restrictions
416	jsr166	1.11	* @throws NullPointerException if {@code e} is null and this
417	dl	1.3	* 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	jsr166	1.7	* words, removes and returns the first element of this deque.
424	dl	1.3	*
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	jsr166	1.6	*
440	jsr166	1.11	* @return an {@code Iterator} over the elements in this deque
441	dl	1.3	*/
442			Iterator<E> iterator();
443	dl	1.1	}