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/* |
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* Written by Doug Lea and Josh Bloch with assistance from members of |
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* JCP JSR-166 Expert Group and released to the public domain, as explained |
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* at http://creativecommons.org/licenses/publicdomain |
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* at http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package java.util; |
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/** |
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* A linear collection that supports element insertion and removal at |
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* both ends. The name <i>deque</i> is short for "double ended queue" |
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* and is usually pronounced "deck". Most <tt>Deque</tt> |
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* and is usually pronounced "deck". Most {@code Deque} |
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* implementations place no fixed limits on the number of elements |
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* they may contain, but this interface supports capacity-restricted |
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* deques as well as those with no fixed size limit. |
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* ends of the deque. Methods are provided to insert, remove, and |
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* examine the element. Each of these methods exists in two forms: |
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* one throws an exception if the operation fails, the other returns a |
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* special value (either <tt>null</tt> or <tt>false</tt>, depending on |
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* special value (either {@code null} or {@code false}, depending on |
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* the operation). The latter form of the insert operation is |
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* designed specifically for use with capacity-restricted |
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* <tt>Deque</tt> implementations; in most implementations, insert |
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* {@code Deque} implementations; in most implementations, insert |
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* operations cannot fail. |
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* |
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* <p>The twelve methods described above are summarized in the |
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* following table: |
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* |
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* <p><table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <p> |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <caption>Summary of Deque methods</caption> |
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* <tr> |
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* <td></td> |
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* <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td> |
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* <tr> |
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* <td></td> |
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* <td ALIGN=CENTER><em>Throws exception</em></td> |
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* <td ALIGN=CENTER><em>Returns special value</em></td> |
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* <td ALIGN=CENTER><em>Special value</em></td> |
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* <td ALIGN=CENTER><em>Throws exception</em></td> |
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* <td ALIGN=CENTER><em>Returns special value</em></td> |
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* <td ALIGN=CENTER><em>Special value</em></td> |
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* </tr> |
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* <tr> |
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* <td><b>Insert</b></td> |
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* <p>This interface extends the {@link Queue} interface. When a deque is |
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* used as a queue, FIFO (First-In-First-Out) behavior results. Elements are |
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* added at the end of the deque and removed from the beginning. The methods |
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* inherited from the <tt>Queue</tt> interface are precisely equivalent to |
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* <tt>Deque</tt> methods as indicated in the following table: |
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* inherited from the {@code Queue} interface are precisely equivalent to |
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* {@code Deque} methods as indicated in the following table: |
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* |
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* <p><table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <p> |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <caption>Comparison of Queue and Deque methods</caption> |
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* <tr> |
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* <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td> |
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* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#offer offer(e)}</td> |
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* <td>{@link #offerLast offerLast(e)}</td> |
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* <td ALIGN=CENTER> <b>{@code Queue} Method</b></td> |
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* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#add add(e)}</td> |
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* <td>{@link #addLast addLast(e)}</td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#poll poll()}</td> |
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* <td>{@link #pollFirst pollFirst()}</td> |
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* <td>{@link java.util.Queue#offer offer(e)}</td> |
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* <td>{@link #offerLast offerLast(e)}</td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#remove remove()}</td> |
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* <td>{@link #removeFirst removeFirst()}</td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#peek peek()}</td> |
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* <td>{@link #peek peekFirst()}</td> |
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* <td>{@link java.util.Queue#poll poll()}</td> |
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* <td>{@link #pollFirst pollFirst()}</td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#element element()}</td> |
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* <td>{@link #getFirst getFirst()}</td> |
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* </tr> |
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* <tr> |
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* <td>{@link java.util.Queue#peek peek()}</td> |
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* <td>{@link #peek peekFirst()}</td> |
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* </tr> |
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* </table> |
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* |
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* <p>Deques can also be used as LIFO (Last-In-First-Out) stacks. This |
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* interface should be used in preference to the legacy {@link Stack} class. |
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* When a deque is used as a stack, elements are pushed and popped from the |
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* beginning of the deque. Stack methods are precisely equivalent to |
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* <tt>Deque</tt> methods as indicated in the table below: |
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* {@code Deque} methods as indicated in the table below: |
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* |
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* <p><table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <p> |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <caption>Comparison of Stack and Deque methods</caption> |
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* <tr> |
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* <td ALIGN=CENTER> <b>Stack Method</b></td> |
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* <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td> |
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* <td ALIGN=CENTER> <b>Equivalent {@code Deque} Method</b></td> |
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* </tr> |
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* <tr> |
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* <td>{@link #push push(e)}</td> |
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* |
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* <p>This interface provides two methods to remove interior |
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* elements, {@link #removeFirstOccurrence removeFirstOccurrence} and |
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* {@link #removeLastOccurrence removeLastOccurrence}. Unlike the |
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* {@link List} interface, this interface does not provide support for |
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* indexed access to elements. |
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* {@link #removeLastOccurrence removeLastOccurrence}. |
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* |
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* <p>Unlike the {@link List} interface, this interface does not |
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* provide support for indexed access to elements. |
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* |
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* <p>While <tt>Deque</tt> implementations are not strictly required |
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* <p>While {@code Deque} implementations are not strictly required |
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* to prohibit the insertion of null elements, they are strongly |
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* encouraged to do so. Users of any <tt>Deque</tt> implementations |
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* encouraged to do so. Users of any {@code Deque} implementations |
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* that do allow null elements are strongly encouraged <i>not</i> to |
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* take advantage of the ability to insert nulls. This is so because |
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* <tt>null</tt> is used as a special return value by various methods |
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* {@code null} is used as a special return value by various methods |
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* to indicated that the deque is empty. |
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* |
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* <p><tt>Deque</tt> implementations generally do not define |
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* element-based versions of the <tt>equals</tt> and <tt>hashCode</tt> |
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* <p>{@code Deque} implementations generally do not define |
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* element-based versions of the {@code equals} and {@code hashCode} |
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* methods, but instead inherit the identity-based versions from class |
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* <tt>Object</tt>. |
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* {@code Object}. |
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* |
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* <p>This interface is a member of the <a |
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* href="{@docRoot}/../guide/collections/index.html"> Java Collections |
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* href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections |
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* Framework</a>. |
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* |
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* @author Doug Lea |
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* @since 1.6 |
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* @param <E> the type of elements held in this collection |
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*/ |
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– |
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public interface Deque<E> extends Queue<E> { |
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/** |
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* Inserts the specified element at the front of this deque if it is |
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* possible to do so immediately without violating capacity restrictions, |
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* throwing an {@code IllegalStateException} if no space is currently |
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* available. When using a capacity-restricted deque, it is generally |
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* preferable to use method {@link #offerFirst}. |
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* |
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* @param e the element to add |
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* @throws IllegalStateException if the element cannot be added at this |
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* time due to capacity restrictions |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this deque |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this deque |
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*/ |
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void addFirst(E e); |
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|
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/** |
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* Inserts the specified element at the end of this deque if it is |
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* possible to do so immediately without violating capacity restrictions, |
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* throwing an {@code IllegalStateException} if no space is currently |
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* available. When using a capacity-restricted deque, it is generally |
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* preferable to use method {@link #offerLast}. |
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* |
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* <p>This method is equivalent to {@link #add}. |
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* |
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* @param e the element to add |
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* @throws IllegalStateException if the element cannot be added at this |
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* time due to capacity restrictions |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this deque |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this deque |
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*/ |
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void addLast(E e); |
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|
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/** |
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* Inserts the specified element at the front of this deque unless it would |
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* violate capacity restrictions. When using a capacity-restricted deque, |
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* this method is generally preferable to method <tt>addFirst</tt>, which |
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* can fail to insert an element only by throwing an exception. |
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* this method is generally preferable to the {@link #addFirst} method, |
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* which can fail to insert an element only by throwing an exception. |
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* |
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* @param e the element to insert |
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* @return <tt>true</tt> if it was possible to insert the element, |
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* else <tt>false</tt> |
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* @param e the element to add |
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* @return {@code true} if the element was added to this deque, else |
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* {@code false} |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this deque |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements |
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* deque does not permit null elements |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this deque |
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*/ |
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boolean offerFirst(E e); |
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|
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/** |
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* Inserts the specified element at the end of this deque unless it would |
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* violate capacity restrictions. When using a capacity-restricted deque, |
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* this method is generally preferable to method <tt>addLast</tt> which |
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* can fail to insert an element only by throwing an exception. |
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* this method is generally preferable to the {@link #addLast} method, |
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* which can fail to insert an element only by throwing an exception. |
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* |
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* @param e the element to insert |
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* @return <tt>true</tt> if it was possible to insert the element, |
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* else <tt>false</tt> |
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* @param e the element to add |
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* @return {@code true} if the element was added to this deque, else |
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* {@code false} |
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* @throws ClassCastException if the class of the specified element |
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* prevents it from being added to this deque |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements |
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* deque does not permit null elements |
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* @throws IllegalArgumentException if some property of the specified |
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* element prevents it from being added to this deque |
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*/ |
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boolean offerLast(E e); |
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|
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/** |
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* Inserts the specified element at the front of this deque unless it |
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* would violate capacity restrictions. |
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* Retrieves and removes the first element of this deque. This method |
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* differs from {@link #pollFirst pollFirst} only in that it throws an |
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* exception if this deque is empty. |
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* |
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* @param e the element to insert |
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* @throws IllegalStateException if it was not possible to insert |
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* the element due to capacity restrictions |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements |
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* @return the head of this deque |
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* @throws NoSuchElementException if this deque is empty |
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*/ |
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void addFirst(E e); |
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E removeFirst(); |
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|
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/** |
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* Inserts the specified element at the end of this deque unless it would |
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* violate capacity restrictions. |
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> |
* Retrieves and removes the last element of this deque. This method |
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* differs from {@link #pollLast pollLast} only in that it throws an |
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* exception if this deque is empty. |
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* |
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* @param e the element to insert |
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* @throws IllegalStateException if it was not possible to insert |
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* the element due to capacity restrictions |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements |
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* @return the tail of this deque |
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* @throws NoSuchElementException if this deque is empty |
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*/ |
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< |
void addLast(E e); |
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> |
E removeLast(); |
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|
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/** |
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* Retrieves and removes the first element of this deque, or |
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* <tt>null</tt> if this deque is empty. |
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> |
* Retrieves and removes the first element of this deque, |
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* or returns {@code null} if this deque is empty. |
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* |
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< |
* @return the first element of this deque, or <tt>null</tt> if |
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* this deque is empty |
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> |
* @return the head of this deque, or {@code null} if this deque is empty |
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*/ |
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E pollFirst(); |
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|
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/** |
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< |
* Retrieves and removes the last element of this deque, or |
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* <tt>null</tt> if this deque is empty. |
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> |
* Retrieves and removes the last element of this deque, |
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> |
* or returns {@code null} if this deque is empty. |
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* |
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< |
* @return the last element of this deque, or <tt>null</tt> if |
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* this deque is empty |
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> |
* @return the tail of this deque, or {@code null} if this deque is empty |
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*/ |
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E pollLast(); |
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|
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/** |
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< |
* Retrieves and removes the first element of this deque. This method |
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< |
* differs from the {@link #pollFirst} method only in that it throws an |
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< |
* exception if this deque is empty. |
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> |
* Retrieves, but does not remove, the first element of this deque. |
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> |
* |
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> |
* This method differs from {@link #peekFirst peekFirst} only in that it |
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* throws an exception if this deque is empty. |
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* |
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< |
* @return the first element of this deque |
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> |
* @return the head of this deque |
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* @throws NoSuchElementException if this deque is empty |
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*/ |
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< |
E removeFirst(); |
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> |
E getFirst(); |
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|
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/** |
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< |
* Retrieves and removes the last element of this deque. This method |
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< |
* differs from the {@link #pollLast} method only in that it throws an |
| 294 |
< |
* exception if this deque is empty. |
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> |
* Retrieves, but does not remove, the last element of this deque. |
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> |
* This method differs from {@link #peekLast peekLast} only in that it |
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> |
* throws an exception if this deque is empty. |
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* |
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< |
* @return the last element of this deque |
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> |
* @return the tail of this deque |
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* @throws NoSuchElementException if this deque is empty |
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*/ |
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< |
E removeLast(); |
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> |
E getLast(); |
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|
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/** |
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* Retrieves, but does not remove, the first element of this deque, |
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< |
* returning <tt>null</tt> if this deque is empty. |
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> |
* or returns {@code null} if this deque is empty. |
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* |
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< |
* @return the first element of this deque, or <tt>null</tt> if |
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< |
* this deque is empty |
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> |
* @return the head of this deque, or {@code null} if this deque is empty |
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*/ |
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E peekFirst(); |
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|
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/** |
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* Retrieves, but does not remove, the last element of this deque, |
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< |
* returning <tt>null</tt> if this deque is empty. |
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> |
* or returns {@code null} if this deque is empty. |
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* |
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< |
* @return the last element of this deque, or <tt>null</tt> if this deque |
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< |
* is empty |
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> |
* @return the tail of this deque, or {@code null} if this deque is empty |
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*/ |
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E peekLast(); |
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|
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/** |
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< |
* Retrieves, but does not remove, the first element of this |
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< |
* deque. This method differs from the {@link #peekFirst} method only |
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< |
* in that it throws an exception if this deque is empty. |
| 321 |
< |
* |
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< |
* @return the first element of this deque |
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< |
* @throws NoSuchElementException if this deque is empty |
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< |
*/ |
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< |
E getFirst(); |
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< |
|
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< |
/** |
| 281 |
< |
* Retrieves, but does not remove, the last element of this |
| 282 |
< |
* deque. This method differs from the {@link #peekLast} method only |
| 283 |
< |
* in that it throws an exception if this deque is empty. |
| 284 |
< |
* |
| 285 |
< |
* @return the last element of this deque |
| 286 |
< |
* @throws NoSuchElementException if this deque is empty |
| 287 |
< |
*/ |
| 288 |
< |
E getLast(); |
| 289 |
< |
|
| 290 |
< |
/** |
| 291 |
< |
* Removes the first occurrence of the specified element in this |
| 292 |
< |
* deque. If the deque does not contain the element, it is |
| 293 |
< |
* unchanged. More formally, removes the first element <tt>e</tt> |
| 294 |
< |
* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if |
| 295 |
< |
* such an element exists). |
| 318 |
> |
* Removes the first occurrence of the specified element from this deque. |
| 319 |
> |
* If the deque does not contain the element, it is unchanged. |
| 320 |
> |
* More formally, removes the first element {@code e} such that |
| 321 |
> |
* <tt>(o==null ? e==null : o.equals(e))</tt> |
| 322 |
> |
* (if such an element exists). |
| 323 |
> |
* Returns {@code true} if this deque contained the specified element |
| 324 |
> |
* (or equivalently, if this deque changed as a result of the call). |
| 325 |
|
* |
| 326 |
|
* @param o element to be removed from this deque, if present |
| 327 |
< |
* @return <tt>true</tt> if the deque contained the specified element |
| 327 |
> |
* @return {@code true} if an element was removed as a result of this call |
| 328 |
> |
* @throws ClassCastException if the class of the specified element |
| 329 |
> |
* is incompatible with this deque (optional) |
| 330 |
|
* @throws NullPointerException if the specified element is null and this |
| 331 |
< |
* deque does not permit null elements |
| 331 |
> |
* deque does not permit null elements (optional) |
| 332 |
|
*/ |
| 333 |
|
boolean removeFirstOccurrence(Object o); |
| 334 |
|
|
| 335 |
|
/** |
| 336 |
< |
* Removes the last occurrence of the specified element in this |
| 337 |
< |
* deque. If the deque does not contain the element, it is |
| 338 |
< |
* unchanged. More formally, removes the last element <tt>e</tt> |
| 339 |
< |
* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if |
| 340 |
< |
* such an element exists). |
| 336 |
> |
* Removes the last occurrence of the specified element from this deque. |
| 337 |
> |
* If the deque does not contain the element, it is unchanged. |
| 338 |
> |
* More formally, removes the last element {@code e} such that |
| 339 |
> |
* <tt>(o==null ? e==null : o.equals(e))</tt> |
| 340 |
> |
* (if such an element exists). |
| 341 |
> |
* Returns {@code true} if this deque contained the specified element |
| 342 |
> |
* (or equivalently, if this deque changed as a result of the call). |
| 343 |
|
* |
| 344 |
|
* @param o element to be removed from this deque, if present |
| 345 |
< |
* @return <tt>true</tt> if the deque contained the specified element |
| 345 |
> |
* @return {@code true} if an element was removed as a result of this call |
| 346 |
> |
* @throws ClassCastException if the class of the specified element |
| 347 |
> |
* is incompatible with this deque (optional) |
| 348 |
|
* @throws NullPointerException if the specified element is null and this |
| 349 |
< |
* deque does not permit null elements |
| 349 |
> |
* deque does not permit null elements (optional) |
| 350 |
|
*/ |
| 351 |
|
boolean removeLastOccurrence(Object o); |
| 352 |
|
|
| 318 |
– |
|
| 353 |
|
// *** Queue methods *** |
| 354 |
|
|
| 355 |
|
/** |
| 356 |
|
* Inserts the specified element into the queue represented by this deque |
| 357 |
< |
* unless it would violate capacity restrictions. In other words, inserts |
| 358 |
< |
* the specified element at the end of this deque. When using a |
| 359 |
< |
* capacity-restricted deque, this method is generally preferable to the |
| 360 |
< |
* {@link #add} method, which can fail to insert an element only by |
| 361 |
< |
* throwing an exception. |
| 362 |
< |
* |
| 329 |
< |
* <p>This method is equivalent to {@link #offerLast}. |
| 330 |
< |
* |
| 331 |
< |
* @param e the element to insert |
| 332 |
< |
* @return <tt>true</tt> if it was possible to insert the element, |
| 333 |
< |
* else <tt>false</tt> |
| 334 |
< |
* @throws NullPointerException if the specified element is null and this |
| 335 |
< |
* deque does not permit null elements |
| 336 |
< |
*/ |
| 337 |
< |
boolean offer(E e); |
| 338 |
< |
|
| 339 |
< |
/** |
| 340 |
< |
* Inserts the specified element into the queue represented by this |
| 341 |
< |
* deque unless it would violate capacity restrictions. In other words, |
| 342 |
< |
* inserts the specified element as the last element of this deque. |
| 357 |
> |
* (in other words, at the tail of this deque) if it is possible to do so |
| 358 |
> |
* immediately without violating capacity restrictions, returning |
| 359 |
> |
* {@code true} upon success and throwing an |
| 360 |
> |
* {@code IllegalStateException} if no space is currently available. |
| 361 |
> |
* When using a capacity-restricted deque, it is generally preferable to |
| 362 |
> |
* use {@link #offer(Object) offer}. |
| 363 |
|
* |
| 364 |
|
* <p>This method is equivalent to {@link #addLast}. |
| 365 |
|
* |
| 366 |
< |
* @param e the element to insert |
| 367 |
< |
* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
| 368 |
< |
* @throws IllegalStateException if it was not possible to insert |
| 369 |
< |
* the element due to capacity restrictions |
| 366 |
> |
* @param e the element to add |
| 367 |
> |
* @return {@code true} (as specified by {@link Collection#add}) |
| 368 |
> |
* @throws IllegalStateException if the element cannot be added at this |
| 369 |
> |
* time due to capacity restrictions |
| 370 |
> |
* @throws ClassCastException if the class of the specified element |
| 371 |
> |
* prevents it from being added to this deque |
| 372 |
|
* @throws NullPointerException if the specified element is null and this |
| 373 |
< |
* deque does not permit null elements |
| 373 |
> |
* deque does not permit null elements |
| 374 |
> |
* @throws IllegalArgumentException if some property of the specified |
| 375 |
> |
* element prevents it from being added to this deque |
| 376 |
|
*/ |
| 377 |
|
boolean add(E e); |
| 378 |
|
|
| 379 |
|
/** |
| 380 |
< |
* Retrieves and removes the head of the queue represented by |
| 381 |
< |
* this deque, or <tt>null</tt> if this deque is empty. In other words, |
| 382 |
< |
* retrieves and removes the first element of this deque, or <tt>null</tt> |
| 383 |
< |
* if this deque is empty. |
| 380 |
> |
* Inserts the specified element into the queue represented by this deque |
| 381 |
> |
* (in other words, at the tail of this deque) if it is possible to do so |
| 382 |
> |
* immediately without violating capacity restrictions, returning |
| 383 |
> |
* {@code true} upon success and {@code false} if no space is currently |
| 384 |
> |
* available. When using a capacity-restricted deque, this method is |
| 385 |
> |
* generally preferable to the {@link #add} method, which can fail to |
| 386 |
> |
* insert an element only by throwing an exception. |
| 387 |
|
* |
| 388 |
< |
* <p>This method is equivalent to {@link #pollFirst()}. |
| 388 |
> |
* <p>This method is equivalent to {@link #offerLast}. |
| 389 |
|
* |
| 390 |
< |
* @return the first element of this deque, or <tt>null</tt> if |
| 391 |
< |
* this deque is empty |
| 390 |
> |
* @param e the element to add |
| 391 |
> |
* @return {@code true} if the element was added to this deque, else |
| 392 |
> |
* {@code false} |
| 393 |
> |
* @throws ClassCastException if the class of the specified element |
| 394 |
> |
* prevents it from being added to this deque |
| 395 |
> |
* @throws NullPointerException if the specified element is null and this |
| 396 |
> |
* deque does not permit null elements |
| 397 |
> |
* @throws IllegalArgumentException if some property of the specified |
| 398 |
> |
* element prevents it from being added to this deque |
| 399 |
|
*/ |
| 400 |
< |
E poll(); |
| 400 |
> |
boolean offer(E e); |
| 401 |
|
|
| 402 |
|
/** |
| 403 |
< |
* Retrieves and removes the head of the queue represented by this deque. |
| 404 |
< |
* This method differs from the {@link #poll} method only in that it |
| 405 |
< |
* throws an exception if this deque is empty. |
| 403 |
> |
* Retrieves and removes the head of the queue represented by this deque |
| 404 |
> |
* (in other words, the first element of this deque). |
| 405 |
> |
* This method differs from {@link #poll poll} only in that it throws an |
| 406 |
> |
* exception if this deque is empty. |
| 407 |
|
* |
| 408 |
|
* <p>This method is equivalent to {@link #removeFirst()}. |
| 409 |
|
* |
| 413 |
|
E remove(); |
| 414 |
|
|
| 415 |
|
/** |
| 416 |
< |
* Retrieves, but does not remove, the head of the queue represented by |
| 417 |
< |
* this deque, returning <tt>null</tt> if this deque is empty. |
| 416 |
> |
* Retrieves and removes the head of the queue represented by this deque |
| 417 |
> |
* (in other words, the first element of this deque), or returns |
| 418 |
> |
* {@code null} if this deque is empty. |
| 419 |
|
* |
| 420 |
< |
* <p>This method is equivalent to {@link #peekFirst()}. |
| 420 |
> |
* <p>This method is equivalent to {@link #pollFirst()}. |
| 421 |
|
* |
| 422 |
< |
* @return the head of the queue represented by this deque, or |
| 423 |
< |
* <tt>null</tt> if this deque is empty |
| 422 |
> |
* @return the first element of this deque, or {@code null} if |
| 423 |
> |
* this deque is empty |
| 424 |
|
*/ |
| 425 |
< |
E peek(); |
| 425 |
> |
E poll(); |
| 426 |
|
|
| 427 |
|
/** |
| 428 |
|
* Retrieves, but does not remove, the head of the queue represented by |
| 429 |
< |
* this deque. This method differs from the {@link #peek} method only in |
| 430 |
< |
* that it throws an exception if this deque is empty. |
| 429 |
> |
* this deque (in other words, the first element of this deque). |
| 430 |
> |
* This method differs from {@link #peek peek} only in that it throws an |
| 431 |
> |
* exception if this deque is empty. |
| 432 |
|
* |
| 433 |
|
* <p>This method is equivalent to {@link #getFirst()}. |
| 434 |
|
* |
| 437 |
|
*/ |
| 438 |
|
E element(); |
| 439 |
|
|
| 440 |
+ |
/** |
| 441 |
+ |
* Retrieves, but does not remove, the head of the queue represented by |
| 442 |
+ |
* this deque (in other words, the first element of this deque), or |
| 443 |
+ |
* returns {@code null} if this deque is empty. |
| 444 |
+ |
* |
| 445 |
+ |
* <p>This method is equivalent to {@link #peekFirst()}. |
| 446 |
+ |
* |
| 447 |
+ |
* @return the head of the queue represented by this deque, or |
| 448 |
+ |
* {@code null} if this deque is empty |
| 449 |
+ |
*/ |
| 450 |
+ |
E peek(); |
| 451 |
+ |
|
| 452 |
|
|
| 453 |
|
// *** Stack methods *** |
| 454 |
|
|
| 455 |
|
/** |
| 456 |
< |
* Pushes an element onto the stack represented by this deque. In other |
| 457 |
< |
* words, inserts the element at the front of this deque unless it would |
| 458 |
< |
* violate capacity restrictions. |
| 456 |
> |
* Pushes an element onto the stack represented by this deque (in other |
| 457 |
> |
* words, at the head of this deque) if it is possible to do so |
| 458 |
> |
* immediately without violating capacity restrictions, throwing an |
| 459 |
> |
* {@code IllegalStateException} if no space is currently available. |
| 460 |
|
* |
| 461 |
|
* <p>This method is equivalent to {@link #addFirst}. |
| 462 |
|
* |
| 463 |
|
* @param e the element to push |
| 464 |
< |
* @throws IllegalStateException if it was not possible to insert |
| 465 |
< |
* the element due to capacity restrictions |
| 464 |
> |
* @throws IllegalStateException if the element cannot be added at this |
| 465 |
> |
* time due to capacity restrictions |
| 466 |
> |
* @throws ClassCastException if the class of the specified element |
| 467 |
> |
* prevents it from being added to this deque |
| 468 |
|
* @throws NullPointerException if the specified element is null and this |
| 469 |
< |
* deque does not permit null elements |
| 469 |
> |
* deque does not permit null elements |
| 470 |
> |
* @throws IllegalArgumentException if some property of the specified |
| 471 |
> |
* element prevents it from being added to this deque |
| 472 |
|
*/ |
| 473 |
|
void push(E e); |
| 474 |
|
|
| 479 |
|
* <p>This method is equivalent to {@link #removeFirst()}. |
| 480 |
|
* |
| 481 |
|
* @return the element at the front of this deque (which is the top |
| 482 |
< |
* of the stack represented by this deque) |
| 482 |
> |
* of the stack represented by this deque) |
| 483 |
|
* @throws NoSuchElementException if this deque is empty |
| 484 |
|
*/ |
| 485 |
|
E pop(); |
| 486 |
|
|
| 487 |
|
|
| 488 |
< |
// *** Collection Method *** |
| 488 |
> |
// *** Collection methods *** |
| 489 |
|
|
| 490 |
|
/** |
| 491 |
< |
* Returns an iterator over the elements in this deque. The elements |
| 492 |
< |
* will be ordered from first (head) to last (tail). |
| 491 |
> |
* Removes the first occurrence of the specified element from this deque. |
| 492 |
> |
* If the deque does not contain the element, it is unchanged. |
| 493 |
> |
* More formally, removes the first element {@code e} such that |
| 494 |
> |
* <tt>(o==null ? e==null : o.equals(e))</tt> |
| 495 |
> |
* (if such an element exists). |
| 496 |
> |
* Returns {@code true} if this deque contained the specified element |
| 497 |
> |
* (or equivalently, if this deque changed as a result of the call). |
| 498 |
|
* |
| 499 |
< |
* @return an <tt>Iterator</tt> over the elements in this deque |
| 499 |
> |
* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
| 500 |
> |
* |
| 501 |
> |
* @param o element to be removed from this deque, if present |
| 502 |
> |
* @return {@code true} if an element was removed as a result of this call |
| 503 |
> |
* @throws ClassCastException if the class of the specified element |
| 504 |
> |
* is incompatible with this deque (optional) |
| 505 |
> |
* @throws NullPointerException if the specified element is null and this |
| 506 |
> |
* deque does not permit null elements (optional) |
| 507 |
> |
*/ |
| 508 |
> |
boolean remove(Object o); |
| 509 |
> |
|
| 510 |
> |
/** |
| 511 |
> |
* Returns {@code true} if this deque contains the specified element. |
| 512 |
> |
* More formally, returns {@code true} if and only if this deque contains |
| 513 |
> |
* at least one element {@code e} such that |
| 514 |
> |
* <tt>(o==null ? e==null : o.equals(e))</tt>. |
| 515 |
> |
* |
| 516 |
> |
* @param o element whose presence in this deque is to be tested |
| 517 |
> |
* @return {@code true} if this deque contains the specified element |
| 518 |
> |
* @throws ClassCastException if the type of the specified element |
| 519 |
> |
* is incompatible with this deque (optional) |
| 520 |
> |
* @throws NullPointerException if the specified element is null and this |
| 521 |
> |
* deque does not permit null elements (optional) |
| 522 |
> |
*/ |
| 523 |
> |
boolean contains(Object o); |
| 524 |
> |
|
| 525 |
> |
/** |
| 526 |
> |
* Returns the number of elements in this deque. |
| 527 |
> |
* |
| 528 |
> |
* @return the number of elements in this deque |
| 529 |
> |
*/ |
| 530 |
> |
public int size(); |
| 531 |
> |
|
| 532 |
> |
/** |
| 533 |
> |
* Returns an iterator over the elements in this deque in proper sequence. |
| 534 |
> |
* The elements will be returned in order from first (head) to last (tail). |
| 535 |
> |
* |
| 536 |
> |
* @return an iterator over the elements in this deque in proper sequence |
| 537 |
|
*/ |
| 538 |
|
Iterator<E> iterator(); |
| 539 |
+ |
|
| 540 |
+ |
/** |
| 541 |
+ |
* Returns an iterator over the elements in this deque in reverse |
| 542 |
+ |
* sequential order. The elements will be returned in order from |
| 543 |
+ |
* last (tail) to first (head). |
| 544 |
+ |
* |
| 545 |
+ |
* @return an iterator over the elements in this deque in reverse |
| 546 |
+ |
* sequence |
| 547 |
+ |
*/ |
| 548 |
+ |
Iterator<E> descendingIterator(); |
| 549 |
+ |
|
| 550 |
|
} |
