src/jsr166x/Deque.java

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

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

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

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

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

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

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

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

    /**
     * Removes and returns the first element of this deque.  This method
     * differs from the <tt>pollFirst</tt> method only in that it throws an
     * exception if this deque is empty.
     *
     * @return the first element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E removeFirst();

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

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

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

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

    /**
     * Retrieves, but does not remove, the last element of this
     * deque.  This method differs from the <tt>peek</tt> method only
     * in that it throws an exception if this deque is empty.
     *
     * @return the last element of this deque
     * @throws NoSuchElementException if this deque is empty
     */
    E 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 e element to be removed from this deque, if present
     * @return <tt>true</tt> if the deque contained the specified element
     * @throws NullPointerException if the specified element is <tt>null</tt>
     */
    boolean removeFirstOccurrence(Object e);

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


    // *** Queue methods ***

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

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

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

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

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

    /**
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque.  This method differs from the <tt>peek</tt> method only in
     * that it throws an exception if this deque is empty.
     *
     * <p>This method is equivalent to {@link #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 <tt>e</tt> is null and this
     *     deque does not permit null elements
     */
    void push(E e);

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


    // *** Collection Method ***

    /**
     * Returns an iterator over the elements in this deque.  The elements
     * will be ordered from first (head) to last (tail).
     * 
     * @return an <tt>Iterator</tt> over the elements in this deque
     */
    Iterator<E> iterator();
}
Revision:	1.4
Committed:	Sun Dec 26 20:13:15 2004 UTC (19 years, 4 months ago) by dl
Branch:	MAIN
Changes since 1.3:	+6 -6 lines
Log Message:	Rename {first,last}Element->get{First,Last}
#	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			* at http://creativecommons.org/licenses/publicdomain
5	dl	1.1	*/
6
7	dl	1.3	package jsr166x; // XXX This belongs in java.util!!! XXX
8			import java.util.*; // XXX This import goes away XXX
9	dl	1.1
10			/**
11	dl	1.3	* A linear collection that supports element insertion and removal
12			* at both ends. The name <i>deque</i> is short for "double ended
13			* queue" and is usually pronounced "deck". Most <tt>Deque</tt>
14			* implementations place no fixed limits on the number of elements
15			* they may contain, but this interface supports capacity-restricted
16			* deques as well as those with no fixed size limit.
17			*
18			* <p>This interface defines methods to access the elements at both ends of
19			* the deque. Methods are provided to insert, remove, and examine the
20			* element. Each of these methods exists in two forms: one throws an
21			* exception if the operation fails, the other returns a special value (either
22			* <tt>null</tt> or <tt>false</tt>, depending on the operation). The latter
23			* form of the insert operation is designed specifically for use with
24			* capacity-restricted <tt>Deque</tt> implementations; in most implementations,
25			* insert operations cannot fail.
26			*
27			* <p>The twelve methods described above are are summarized in the
28			* follwoing table:<p>
29			*
30			* <table BORDER CELLPADDING=3 CELLSPACING=1>
31			* <tr>
32			* <td></td>
33			* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
34			* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td>
35			* </tr>
36			* <tr>
37			* <td></td>
38			* <td ALIGN=CENTER><em>Throws exception</em></td>
39			* <td ALIGN=CENTER><em>Returns special value</em></td>
40			* <td ALIGN=CENTER><em>Throws exception</em></td>
41			* <td ALIGN=CENTER><em>Returns special value</em></td>
42			* </tr>
43			* <tr>
44			* <td><b>Insert</b></td>
45			* <td>{@link #addFirst addFirst(e)}</td>
46			* <td>{@link #offerFirst offerFirst(e)}</td>
47			* <td>{@link #addLast addLast(e)}</td>
48			* <td>{@link #offerLast offerLast(e)}</td>
49			* </tr>
50			* <tr>
51			* <td><b>Remove</b></td>
52			* <td>{@link #removeFirst removeFirst()}</td>
53			* <td>{@link #pollFirst pollFirst()}</td>
54			* <td>{@link #removeLast removeLast()}</td>
55			* <td>{@link #pollLast pollLast()}</td>
56			* </tr>
57			* <tr>
58			* <td><b>Examine</b></td>
59	dl	1.4	* <td>{@link #getFirst getFirst()}</td>
60	dl	1.3	* <td>{@link #peekFirst peekFirst()}</td>
61	dl	1.4	* <td>{@link #getLast getLast()}</td>
62	dl	1.3	* <td>{@link #peekLast peekLast()}</td>
63			* </tr>
64			* </table>
65			*
66			* <p>This interface extends the {@link Queue} interface. When a deque is
67			* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are
68			* added to the end of the deque and removed from the beginning. The methods
69			* inherited from the <tt>Queue</tt> interface are precisely equivalent to
70			* <tt>Deque</tt> methods as indicated in the following table:<p>
71			*
72			* <table BORDER CELLPADDING=3 CELLSPACING=1>
73			* <tr>
74			* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
75			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
76			* </tr>
77			* <tr>
78			* <tr>
79			* <td>{@link java.util.Queue#offer offer(e)}</td>
80			* <td>{@link #offerLast offerLast(e)}</td>
81			* </tr>
82			* <tr>
83			* <td>{@link java.util.Queue#add add(e)}</td>
84			* <td>{@link #addLast addLast(e)}</td>
85			* </tr>
86			* <tr>
87			* <td>{@link java.util.Queue#poll poll()}</td>
88			* <td>{@link #pollFirst pollFirst()}</td>
89			* </tr>
90			* <tr>
91			* <td>{@link java.util.Queue#remove remove()}</td>
92			* <td>{@link #removeFirst removeFirst()}</td>
93			* </tr>
94			* <tr>
95			* <td>{@link java.util.Queue#peek peek()}</td>
96			* <td>{@link #peek peekFirst()}</td>
97			* </tr>
98			* <tr>
99			* <td>{@link java.util.Queue#element element()}</td>
100	dl	1.4	* <td>{@link #getFirst getFirst()}</td>
101	dl	1.3	* </tr>
102			* </table>
103			*
104			* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This
105			* interface should be used in preference to the legacy {@link Stack} class.
106			* When a dequeue is used as a stack, elements are pushed and popped from the
107			* beginning of the deque. Stack methods are precisely equivalent to
108			* <tt>Deque</tt> methods as indicated in the table below:<p>
109			*
110			* <table BORDER CELLPADDING=3 CELLSPACING=1>
111			* <tr>
112			* <td ALIGN=CENTER> <b>Stack Method</b></td>
113			* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
114			* </tr>
115			* <tr>
116			* <tr>
117			* <td>{@link #push push(e)}</td>
118			* <td>{@link #addFirst addFirst(e)}</td>
119			* </tr>
120			* <tr>
121			* <td>{@link #pop pop()}</td>
122			* <td>{@link #removeFirst removeFirst()}</td>
123			* </tr>
124			* <tr>
125			* <td>{@link #peek peek()}</td>
126			* <td>{@link #peekFirst peekFirst()}</td>
127			* </tr>
128			* </table>
129			* <p>Note that the {@link #peek peek} method works equally well when a deque
130			* is used as a queue or a stack; in either case, elements are drawn from the
131			* beginning of the deque.
132			*
133			* <p>This inteface provides two methods to to remove interior elements,
134			* {@link #removeFirstOccurrence removeFirstOccurrence} and {@link
135			* #removeLastOccurrence removeLastOccurrence}. Unlike the {@link List}
136			* interface, this interface does not provide support for indexed access to
137			* elements.
138			*
139			* <p>While <tt>Deque</tt> implementations are not strictly required to
140			* prohibit the insertion of null elements, they are strongly encouraged to do
141			* so. Users of any <tt>Deque</tt> implementations that do allow null
142			* elements are strongly encouraged <i>not</i> to take advantage of the
143			* ability to insert nulls. This is so because <tt>null</tt> is used as a
144			* special return value by various methods to indicated that the deque is
145			* empty.
146	dl	1.1	*
147			* <p><tt>Deque</tt> implementations generally do not define
148	dl	1.3	* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
149			* methods, but instead inherit the identity-based versions from class
150			* <tt>Object</tt>.
151	dl	1.1	*
152			* <p>This interface is a member of the <a
153			* href="{@docRoot}/../guide/collections/index.html"> Java Collections
154			* Framework</a>.
155			*
156			* @author Doug Lea
157	dl	1.3	* @author Josh Bloch
158			* @since 1.6
159	dl	1.1	* @param <E> the type of elements held in this collection
160			*/
161	dl	1.3	public interface Deque<E> extends Queue<E> {
162	dl	1.1	/**
163	dl	1.3	* Inserts the specified element to the front this deque unless it would
164			* violate capacity restrictions. When using a capacity-restricted deque,
165			* this method is generally preferable to method <tt>addFirst</tt>, which
166			* can fail to insert an element only by throwing an exception.
167	dl	1.1	*
168	dl	1.3	* @param e the element to insert
169			* @return <tt>true</tt> if it was possible to insert the element,
170			* else <tt>false</tt>
171			* @throws NullPointerException if <tt>e</tt> is null and this
172			* deque does not permit null elements
173	dl	1.1	*/
174	dl	1.3	boolean offerFirst(E e);
175	dl	1.1
176			/**
177	dl	1.3	* Inserts the specified element to the end of this deque unless it would
178			* violate capacity restrictions. When using a capacity-restricted deque,
179			* this method is generally preferable to method <tt>addLast</tt> which
180			* can fail to insert an element only by throwing an exception.
181	dl	1.1	*
182	dl	1.3	* @param e the element to insert
183			* @return <tt>true</tt> if it was possible to insert the element,
184			* else <tt>false</tt>
185			* @throws NullPointerException if <tt>e</tt> is null and this
186			* deque does not permit null elements
187	dl	1.1	*/
188	dl	1.3	boolean offerLast(E e);
189	dl	1.1
190			/**
191	dl	1.3	* Inserts the specified element to the front of this deque unless it
192			* would violate capacity restrictions.
193	dl	1.1	*
194	dl	1.3	* @param e the element to insert
195			* @throws IllegalStateException if it was not possible to insert
196			* the element due to capacity restrictions
197			* @throws NullPointerException if <tt>e</tt> is null and this
198			* deque does not permit null elements
199	dl	1.1	*/
200	dl	1.3	void addFirst(E e);
201	dl	1.1
202			/**
203	dl	1.3	* Inserts the specified element to the end of this deque unless it would
204			* violate capacity restrictions.
205	dl	1.1	*
206	dl	1.3	* @param e the element to insert
207			* @throws IllegalStateException if it was not possible to insert
208			* the element due to capacity restrictions
209			* @throws NullPointerException if <tt>e</tt> is null and this
210			* deque does not permit null elements
211	dl	1.1	*/
212	dl	1.3	void addLast(E e);
213	dl	1.1
214			/**
215			* Retrieves and removes the first element of this deque, or
216			* <tt>null</tt> if this deque is empty.
217			*
218			* @return the first element of this deque, or <tt>null</tt> if
219	dl	1.3	* this deque is empty
220	dl	1.1	*/
221			E pollFirst();
222
223			/**
224			* Retrieves and removes the last element of this deque, or
225			* <tt>null</tt> if this deque is empty.
226			*
227			* @return the last element of this deque, or <tt>null</tt> if
228	dl	1.3	* this deque is empty
229	dl	1.1	*/
230			E pollLast();
231
232			/**
233	dl	1.3	* Removes and returns the first element of this deque. This method
234			* differs from the <tt>pollFirst</tt> method only in that it throws an
235	dl	1.1	* exception if this deque is empty.
236			*
237	dl	1.3	* @return the first element of this deque
238			* @throws NoSuchElementException if this deque is empty
239	dl	1.1	*/
240			E removeFirst();
241
242			/**
243			* Retrieves and removes the last element of this deque. This method
244	dl	1.3	* differs from the <tt>pollLast</tt> method only in that it throws an
245	dl	1.1	* exception if this deque is empty.
246			*
247	dl	1.3	* @return the last element of this deque
248			* @throws NoSuchElementException if this deque is empty
249	dl	1.1	*/
250			E removeLast();
251
252			/**
253			* Retrieves, but does not remove, the first element of this deque,
254			* returning <tt>null</tt> if this deque is empty.
255			*
256			* @return the first element of this deque, or <tt>null</tt> if
257	dl	1.3	* this deque is empty
258	dl	1.1	*/
259			E peekFirst();
260
261			/**
262			* Retrieves, but does not remove, the last element of this deque,
263			* returning <tt>null</tt> if this deque is empty.
264			*
265			* @return the last element of this deque, or <tt>null</tt> if this deque
266	dl	1.3	* is empty
267	dl	1.1	*/
268			E peekLast();
269
270			/**
271			* Retrieves, but does not remove, the first element of this
272			* deque. This method differs from the <tt>peek</tt> method only
273			* in that it throws an exception if this deque is empty.
274			*
275	dl	1.3	* @return the first element of this deque
276			* @throws NoSuchElementException if this deque is empty
277	dl	1.1	*/
278	dl	1.4	E getFirst();
279	dl	1.1
280			/**
281			* Retrieves, but does not remove, the last element of this
282			* deque. This method differs from the <tt>peek</tt> method only
283			* in that it throws an exception if this deque is empty.
284			*
285	dl	1.3	* @return the last element of this deque
286			* @throws NoSuchElementException if this deque is empty
287	dl	1.1	*/
288	dl	1.4	E getLast();
289	dl	1.1
290			/**
291			* Removes the first occurrence of the specified element in this
292			* deque. If the deque does not contain the element, it is
293			* unchanged. More formally, removes the first element <tt>e</tt>
294			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
295			* such an element exists).
296			*
297	dl	1.3	* @param e element to be removed from this deque, if present
298			* @return <tt>true</tt> if the deque contained the specified element
299	dl	1.1	* @throws NullPointerException if the specified element is <tt>null</tt>
300			*/
301	dl	1.3	boolean removeFirstOccurrence(Object e);
302	dl	1.1
303			/**
304			* Removes the last occurrence of the specified element in this
305			* deque. If the deque does not contain the element, it is
306			* unchanged. More formally, removes the last element <tt>e</tt>
307			* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if
308			* such an element exists).
309			*
310	dl	1.3	* @param e element to be removed from this deque, if present
311			* @return <tt>true</tt> if the deque contained the specified element
312	dl	1.1	* @throws NullPointerException if the specified element is <tt>null</tt>
313			*/
314	dl	1.3	boolean removeLastOccurrence(Object e);
315
316
317			// * Queue methods *
318	dl	1.1
319			/**
320	dl	1.3	* Inserts the specified element into the queue represented by this deque
321			* unless it would violate capacity restrictions. In other words, inserts
322			* the specified element to the end of this deque. When using a
323			* capacity-restricted deque, this method is generally preferable to the
324			* {@link #add} method, which can fail to insert an element only by
325			* throwing an exception.
326			*
327			* <p>This method is equivalent to {@link #offerLast}.
328			*
329			* @param e the element to insert
330			* @return <tt>true</tt> if it was possible to insert the element,
331			* else <tt>false</tt>
332			* @throws NullPointerException if <tt>e</tt> is null and this
333			* deque does not permit null elements
334	dl	1.1	*/
335	dl	1.3	boolean offer(E e);
336	dl	1.1
337			/**
338	dl	1.3	* Inserts the specified element into the queue represented by this
339			* deque unless it would violate capacity restrictions. In other words,
340			* inserts the specified element as the last element of this deque.
341			*
342			* <p>This method is equivalent to {@link #addLast}.
343			*
344			* @param e the element to insert
345			* @return <tt>true</tt> (as per the spec for {@link Collection#add})
346			* @throws IllegalStateException if it was not possible to insert
347			* the element due to capacity restrictions
348			* @throws NullPointerException if <tt>e</tt> is null and this
349			* deque does not permit null elements
350			*/
351			boolean add(E e);
352
353			/**
354			* Retrieves and removes the head of the queue represented by
355			* this deque, or <tt>null</tt> if this deque is empty. In other words,
356			* retrieves and removes the first element of this deque, or <tt>null</tt>
357			* if this deque is empty.
358			*
359			* <p>This method is equivalent to {@link #pollFirst()}.
360			*
361			* @return the first element of this deque, or <tt>null</tt> if
362			* this deque is empty
363			*/
364			E poll();
365
366			/**
367			* Retrieves and removes the head of the queue represented by this deque.
368			* This method differs from the <tt>poll</tt> method only in that it
369			* throws an exception if this deque is empty.
370			*
371			* <p>This method is equivalent to {@link #removeFirst()}.
372			*
373			* @return the head of the queue represented by this deque
374			* @throws NoSuchElementException if this deque is empty
375	dl	1.1	*/
376	dl	1.3	E remove();
377	dl	1.1
378	dl	1.3	/**
379			* Retrieves, but does not remove, the head of the queue represented by
380			* this deque, returning <tt>null</tt> if this deque is empty.
381			*
382			* <p>This method is equivalent to {@link #peekFirst()}
383			*
384			* @return the head of the queue represented by this deque, or
385			* <tt>null</tt> if this deque is empty
386			*/
387			E peek();
388
389			/**
390			* Retrieves, but does not remove, the head of the queue represented by
391			* this deque. This method differs from the <tt>peek</tt> method only in
392			* that it throws an exception if this deque is empty.
393			*
394	dl	1.4	* <p>This method is equivalent to {@link #getFirst()}
395	dl	1.3	*
396			* @return the head of the queue represented by this deque
397			* @throws NoSuchElementException if this deque is empty
398			*/
399			E element();
400
401
402			// * Stack methods *
403
404			/**
405			* Pushes an element onto the stack represented by this deque. In other
406			* words, inserts the element to the front this deque unless it would
407			* violate capacity restrictions.
408			*
409			* <p>This method is equivalent to {@link #addFirst}.
410			*
411			* @throws IllegalStateException if it was not possible to insert
412			* the element due to capacity restrictions
413			* @throws NullPointerException if <tt>e</tt> is null and this
414			* deque does not permit null elements
415			*/
416			void push(E e);
417
418			/**
419			* Pops an element from the stack represented by this deque. In other
420			* words, removes and returns the the first element of this deque.
421			*
422			* <p>This method is equivalent to {@link #removeFirst()}.
423			*
424			* @return the element at the front of this deque (which is the top
425			* of the stack represented by this deque)
426			* @throws NoSuchElementException if this deque is empty
427			*/
428			E pop();
429
430
431			// * Collection Method *
432
433			/**
434			* Returns an iterator over the elements in this deque. The elements
435			* will be ordered from first (head) to last (tail).
436			*
437			* @return an <tt>Iterator</tt> over the elements in this deque
438			*/
439			Iterator<E> iterator();
440	dl	1.1	}