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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/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util; |
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|
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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 {@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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* |
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* <p>This interface defines methods to access the elements at both |
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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 {@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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* {@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> |
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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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* <td ALIGN=CENTER COLSPAN = 2> <b>Last Element (Tail)</b></td> |
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* </tr> |
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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>Special value</em></td> |
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* <td ALIGN=CENTER><em>Throws exception</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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* <td>{@link Deque#addFirst addFirst(e)}</td> |
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* <td>{@link Deque#offerFirst offerFirst(e)}</td> |
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* <td>{@link Deque#addLast addLast(e)}</td> |
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* <td>{@link Deque#offerLast offerLast(e)}</td> |
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* </tr> |
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* <tr> |
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* <td><b>Remove</b></td> |
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* <td>{@link Deque#removeFirst removeFirst()}</td> |
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* <td>{@link Deque#pollFirst pollFirst()}</td> |
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* <td>{@link Deque#removeLast removeLast()}</td> |
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* <td>{@link Deque#pollLast pollLast()}</td> |
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* </tr> |
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* <tr> |
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* <td><b>Examine</b></td> |
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* <td>{@link Deque#getFirst getFirst()}</td> |
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* <td>{@link Deque#peekFirst peekFirst()}</td> |
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* <td>{@link Deque#getLast getLast()}</td> |
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* <td>{@link Deque#peekLast peekLast()}</td> |
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* </tr> |
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* </table> |
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* |
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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 {@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> |
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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>{@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#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#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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* {@code Deque} methods as indicated in the table below: |
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* |
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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 {@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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* <td>{@link #addFirst addFirst(e)}</td> |
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* </tr> |
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* <tr> |
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* <td>{@link #pop pop()}</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 #peek peek()}</td> |
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* <td>{@link #peekFirst peekFirst()}</td> |
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* </tr> |
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* </table> |
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* |
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* <p>Note that the {@link #peek peek} method works equally well when |
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* a deque is used as a queue or a stack; in either case, elements are |
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* drawn from the beginning of the deque. |
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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}. |
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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 {@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 {@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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* {@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>{@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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* {@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}/../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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* @author Josh Bloch |
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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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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 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 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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* @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 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 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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* @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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* 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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* @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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|
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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 {@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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* @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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|
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/** |
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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 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, |
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* or returns {@code null} if this deque is empty. |
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* |
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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, 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 head 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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/** |
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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 tail of this deque |
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* @throws NoSuchElementException if this deque is empty |
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*/ |
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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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* or returns {@code null} if this deque is empty. |
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* |
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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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* or returns {@code null} if this deque is empty. |
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* |
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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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* Removes the first occurrence of the specified element from this deque. |
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* If the deque does not contain the element, it is unchanged. |
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* More formally, removes the first element {@code e} such that |
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* <tt>(o==null ? e==null : o.equals(e))</tt> |
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* (if such an element exists). |
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* Returns {@code true} if this deque contained the specified element |
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* (or equivalently, if this deque changed as a result of the call). |
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* |
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* @param o element to be removed from this deque, if present |
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* @return {@code true} if an element was removed as a result of this call |
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* @throws ClassCastException if the class of the specified element |
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* is incompatible with this deque (optional) |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements (optional) |
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*/ |
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boolean removeFirstOccurrence(Object o); |
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|
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/** |
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* Removes the last occurrence of the specified element from this deque. |
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* If the deque does not contain the element, it is unchanged. |
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* More formally, removes the last element {@code e} such that |
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* <tt>(o==null ? e==null : o.equals(e))</tt> |
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* (if such an element exists). |
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* Returns {@code true} if this deque contained the specified element |
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* (or equivalently, if this deque changed as a result of the call). |
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* |
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* @param o element to be removed from this deque, if present |
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* @return {@code true} if an element was removed as a result of this call |
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* @throws ClassCastException if the class of the specified element |
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* is incompatible with this deque (optional) |
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* @throws NullPointerException if the specified element is null and this |
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* deque does not permit null elements (optional) |
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*/ |
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boolean removeLastOccurrence(Object o); |
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|
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// *** Queue methods *** |
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|
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/** |
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* Inserts the specified element into the queue represented by this deque |
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* (in other words, at the tail of this deque) if it is possible to do so |
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* immediately without violating capacity restrictions, returning |
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* {@code true} upon success and throwing an |
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* {@code IllegalStateException} if no space is currently available. |
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* When using a capacity-restricted deque, it is generally preferable to |
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* use {@link #offer(Object) offer}. |
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* |
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* <p>This method is equivalent to {@link #addLast}. |
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* |
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* @param e the element to add |
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* @return {@code true} (as specified by {@link Collection#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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boolean add(E e); |
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|
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/** |
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* Inserts the specified element into the queue represented by this deque |
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* (in other words, at the tail of this deque) if it is possible to do so |
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* immediately without violating capacity restrictions, returning |
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* {@code true} upon success and {@code false} if no space is currently |
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* available. When using a capacity-restricted deque, this method is |
385 |
* generally preferable to the {@link #add} method, which can fail to |
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* insert an element only by throwing an exception. |
387 |
* |
388 |
* <p>This method is equivalent to {@link #offerLast}. |
389 |
* |
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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 |
392 |
* {@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 |
396 |
* 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 |
399 |
*/ |
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boolean offer(E e); |
401 |
|
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/** |
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* Retrieves and removes the head of the queue represented by this deque |
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* (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 |
* |
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* <p>This method is equivalent to {@link #removeFirst()}. |
409 |
* |
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* @return the head of the queue represented by this deque |
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* @throws NoSuchElementException if this deque is empty |
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*/ |
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E remove(); |
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|
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/** |
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 #pollFirst()}. |
421 |
* |
422 |
* @return the first element of this deque, or {@code null} if |
423 |
* this deque is empty |
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*/ |
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E poll(); |
426 |
|
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/** |
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* Retrieves, but does not remove, the head of the queue represented by |
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 |
* |
435 |
* @return the head of the queue represented by this deque |
436 |
* @throws NoSuchElementException if this deque is empty |
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 |
* |
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* @return the head of the queue represented by this deque, or |
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* {@code null} if this deque is empty |
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*/ |
450 |
E peek(); |
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|
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|
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// *** Stack methods *** |
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|
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/** |
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* Pushes an element onto the stack represented by this deque (in other |
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* words, at the head of this deque) if it is possible to do so |
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* 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 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 |
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 |
|
475 |
/** |
476 |
* Pops an element from the stack represented by this deque. In other |
477 |
* words, removes and returns the first element of this deque. |
478 |
* |
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) |
483 |
* @throws NoSuchElementException if this deque is empty |
484 |
*/ |
485 |
E pop(); |
486 |
|
487 |
|
488 |
// *** Collection methods *** |
489 |
|
490 |
/** |
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 |
* <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 |
} |