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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:<p> |
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* following table: |
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* |
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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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* <td>{@link #addFirst addFirst(e)}</td> |
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* <td>{@link #offerFirst offerFirst(e)}</td> |
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* <td>{@link #addLast addLast(e)}</td> |
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* <td>{@link #offerLast offerLast(e)}</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 #removeFirst removeFirst()}</td> |
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* <td>{@link #pollFirst pollFirst()}</td> |
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* <td>{@link #removeLast removeLast()}</td> |
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* <td>{@link #pollLast pollLast()}</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 #getFirst getFirst()}</td> |
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* <td>{@link #peekFirst peekFirst()}</td> |
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* <td>{@link #getLast getLast()}</td> |
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* <td>{@link #peekLast peekLast()}</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 <tt>Queue</tt> interface are precisely equivalent to |
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* <tt>Deque</tt> methods as indicated in the following table:<p> |
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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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* <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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* <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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* <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#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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* </tr> |
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* <tr> |
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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#peek peek()}</td> |
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* <td>{@link #peek peekFirst()}</td> |
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* </tr> |
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* <tr> |
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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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* <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:<p> |
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* {@code Deque} methods as indicated in the table below: |
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* |
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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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* <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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* </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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* </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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* </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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* |
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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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* @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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* @param <E> the type of elements held in this deque |
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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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* 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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* Removes and returns the first element of this deque. This method |
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* differs from the <tt>pollFirst</tt> 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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* @return the first element of this deque |
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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 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 <tt>pollLast</tt> method only in that it throws an |
291 |
< |
* exception if this deque is empty. |
289 |
> |
* Retrieves, but does not remove, the last element of this deque. |
290 |
> |
* This method differs from {@link #peekLast peekLast} only in that it |
291 |
> |
* throws an exception if this deque is empty. |
292 |
|
* |
293 |
< |
* @return the last element of this deque |
293 |
> |
* @return the tail of this deque |
294 |
|
* @throws NoSuchElementException if this deque is empty |
295 |
|
*/ |
296 |
< |
E removeLast(); |
296 |
> |
E getLast(); |
297 |
|
|
298 |
|
/** |
299 |
|
* Retrieves, but does not remove, the first element of this deque, |
300 |
< |
* returning <tt>null</tt> if this deque is empty. |
300 |
> |
* or returns {@code null} if this deque is empty. |
301 |
|
* |
302 |
< |
* @return the first element of this deque, or <tt>null</tt> if |
259 |
< |
* this deque is empty |
302 |
> |
* @return the head of this deque, or {@code null} if this deque is empty |
303 |
|
*/ |
304 |
|
E peekFirst(); |
305 |
|
|
306 |
|
/** |
307 |
|
* Retrieves, but does not remove, the last element of this deque, |
308 |
< |
* returning <tt>null</tt> if this deque is empty. |
308 |
> |
* or returns {@code null} if this deque is empty. |
309 |
|
* |
310 |
< |
* @return the last element of this deque, or <tt>null</tt> if this deque |
268 |
< |
* is empty |
310 |
> |
* @return the tail of this deque, or {@code null} if this deque is empty |
311 |
|
*/ |
312 |
|
E peekLast(); |
313 |
|
|
314 |
|
/** |
315 |
< |
* Retrieves, but does not remove, the first element of this |
316 |
< |
* deque. This method differs from the <tt>peekFirst</tt> method only |
317 |
< |
* in that it throws an exception if this deque is empty. |
318 |
< |
* |
319 |
< |
* @return the first element of this deque |
320 |
< |
* @throws NoSuchElementException if this deque is empty |
279 |
< |
*/ |
280 |
< |
E getFirst(); |
281 |
< |
|
282 |
< |
/** |
283 |
< |
* Retrieves, but does not remove, the last element of this |
284 |
< |
* deque. This method differs from the <tt>peekLast</tt> method only |
285 |
< |
* in that it throws an exception if this deque is empty. |
286 |
< |
* |
287 |
< |
* @return the last element of this deque |
288 |
< |
* @throws NoSuchElementException if this deque is empty |
289 |
< |
*/ |
290 |
< |
E getLast(); |
291 |
< |
|
292 |
< |
/** |
293 |
< |
* Removes the first occurrence of the specified element in this |
294 |
< |
* deque. If the deque does not contain the element, it is |
295 |
< |
* unchanged. More formally, removes the first element <tt>e</tt> |
296 |
< |
* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if |
297 |
< |
* such an element exists). |
315 |
> |
* Removes the first occurrence of the specified element from this deque. |
316 |
> |
* If the deque does not contain the element, it is unchanged. |
317 |
> |
* More formally, removes the first element {@code e} such that |
318 |
> |
* {@code Objects.equals(o, e)} (if such an element exists). |
319 |
> |
* Returns {@code true} if this deque contained the specified element |
320 |
> |
* (or equivalently, if this deque changed as a result of the call). |
321 |
|
* |
322 |
|
* @param o element to be removed from this deque, if present |
323 |
< |
* @return <tt>true</tt> if the deque contained the specified element |
323 |
> |
* @return {@code true} if an element was removed as a result of this call |
324 |
> |
* @throws ClassCastException if the class of the specified element |
325 |
> |
* is incompatible with this deque |
326 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
327 |
|
* @throws NullPointerException if the specified element is null and this |
328 |
< |
* deque does not permit null elements |
328 |
> |
* deque does not permit null elements |
329 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
330 |
|
*/ |
331 |
|
boolean removeFirstOccurrence(Object o); |
332 |
|
|
333 |
|
/** |
334 |
< |
* Removes the last occurrence of the specified element in this |
335 |
< |
* deque. If the deque does not contain the element, it is |
336 |
< |
* unchanged. More formally, removes the last element <tt>e</tt> |
337 |
< |
* such that <tt>(o==null ? e==null : o.equals(e))</tt> (if |
338 |
< |
* such an element exists). |
334 |
> |
* Removes the last occurrence of the specified element from this deque. |
335 |
> |
* If the deque does not contain the element, it is unchanged. |
336 |
> |
* More formally, removes the last element {@code e} such that |
337 |
> |
* {@code Objects.equals(o, e)} (if such an element exists). |
338 |
> |
* Returns {@code true} if this deque contained the specified element |
339 |
> |
* (or equivalently, if this deque changed as a result of the call). |
340 |
|
* |
341 |
|
* @param o element to be removed from this deque, if present |
342 |
< |
* @return <tt>true</tt> if the deque contained the specified element |
342 |
> |
* @return {@code true} if an element was removed as a result of this call |
343 |
> |
* @throws ClassCastException if the class of the specified element |
344 |
> |
* is incompatible with this deque |
345 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
346 |
|
* @throws NullPointerException if the specified element is null and this |
347 |
< |
* deque does not permit null elements |
347 |
> |
* deque does not permit null elements |
348 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
349 |
|
*/ |
350 |
|
boolean removeLastOccurrence(Object o); |
351 |
|
|
320 |
– |
|
352 |
|
// *** Queue methods *** |
353 |
|
|
354 |
|
/** |
355 |
|
* Inserts the specified element into the queue represented by this deque |
356 |
< |
* unless it would violate capacity restrictions. In other words, inserts |
357 |
< |
* the specified element at the end of this deque. When using a |
358 |
< |
* capacity-restricted deque, this method is generally preferable to the |
359 |
< |
* {@link #add} method, which can fail to insert an element only by |
360 |
< |
* throwing an exception. |
361 |
< |
* |
331 |
< |
* <p>This method is equivalent to {@link #offerLast}. |
332 |
< |
* |
333 |
< |
* @param e the element to insert |
334 |
< |
* @return <tt>true</tt> if it was possible to insert the element, |
335 |
< |
* else <tt>false</tt> |
336 |
< |
* @throws NullPointerException if the specified element is null and this |
337 |
< |
* deque does not permit null elements |
338 |
< |
*/ |
339 |
< |
boolean offer(E e); |
340 |
< |
|
341 |
< |
/** |
342 |
< |
* Inserts the specified element into the queue represented by this |
343 |
< |
* deque unless it would violate capacity restrictions. In other words, |
344 |
< |
* inserts the specified element as the last element of this deque. |
356 |
> |
* (in other words, at the tail of this deque) if it is possible to do so |
357 |
> |
* immediately without violating capacity restrictions, returning |
358 |
> |
* {@code true} upon success and throwing an |
359 |
> |
* {@code IllegalStateException} if no space is currently available. |
360 |
> |
* When using a capacity-restricted deque, it is generally preferable to |
361 |
> |
* use {@link #offer(Object) offer}. |
362 |
|
* |
363 |
|
* <p>This method is equivalent to {@link #addLast}. |
364 |
|
* |
365 |
< |
* @param e the element to insert |
366 |
< |
* @return <tt>true</tt> (as per the spec for {@link Collection#add}) |
367 |
< |
* @throws IllegalStateException if it was not possible to insert |
368 |
< |
* the element due to capacity restrictions |
365 |
> |
* @param e the element to add |
366 |
> |
* @return {@code true} (as specified by {@link Collection#add}) |
367 |
> |
* @throws IllegalStateException if the element cannot be added at this |
368 |
> |
* time due to capacity restrictions |
369 |
> |
* @throws ClassCastException if the class of the specified element |
370 |
> |
* prevents it from being added to this deque |
371 |
|
* @throws NullPointerException if the specified element is null and this |
372 |
< |
* deque does not permit null elements |
372 |
> |
* deque does not permit null elements |
373 |
> |
* @throws IllegalArgumentException if some property of the specified |
374 |
> |
* element prevents it from being added to this deque |
375 |
|
*/ |
376 |
|
boolean add(E e); |
377 |
|
|
378 |
|
/** |
379 |
< |
* Retrieves and removes the head of the queue represented by |
380 |
< |
* this deque, or <tt>null</tt> if this deque is empty. In other words, |
381 |
< |
* retrieves and removes the first element of this deque, or <tt>null</tt> |
382 |
< |
* if this deque is empty. |
379 |
> |
* Inserts the specified element into the queue represented by this deque |
380 |
> |
* (in other words, at the tail of this deque) if it is possible to do so |
381 |
> |
* immediately without violating capacity restrictions, returning |
382 |
> |
* {@code true} upon success and {@code false} if no space is currently |
383 |
> |
* available. When using a capacity-restricted deque, this method is |
384 |
> |
* generally preferable to the {@link #add} method, which can fail to |
385 |
> |
* insert an element only by throwing an exception. |
386 |
|
* |
387 |
< |
* <p>This method is equivalent to {@link #pollFirst()}. |
387 |
> |
* <p>This method is equivalent to {@link #offerLast}. |
388 |
|
* |
389 |
< |
* @return the first element of this deque, or <tt>null</tt> if |
390 |
< |
* this deque is empty |
389 |
> |
* @param e the element to add |
390 |
> |
* @return {@code true} if the element was added to this deque, else |
391 |
> |
* {@code false} |
392 |
> |
* @throws ClassCastException if the class of the specified element |
393 |
> |
* prevents it from being added to this deque |
394 |
> |
* @throws NullPointerException if the specified element is null and this |
395 |
> |
* deque does not permit null elements |
396 |
> |
* @throws IllegalArgumentException if some property of the specified |
397 |
> |
* element prevents it from being added to this deque |
398 |
|
*/ |
399 |
< |
E poll(); |
399 |
> |
boolean offer(E e); |
400 |
|
|
401 |
|
/** |
402 |
< |
* Retrieves and removes the head of the queue represented by this deque. |
403 |
< |
* This method differs from the <tt>poll</tt> method only in that it |
404 |
< |
* throws an exception if this deque is empty. |
402 |
> |
* Retrieves and removes the head of the queue represented by this deque |
403 |
> |
* (in other words, the first element of this deque). |
404 |
> |
* This method differs from {@link #poll poll} only in that it throws an |
405 |
> |
* exception if this deque is empty. |
406 |
|
* |
407 |
|
* <p>This method is equivalent to {@link #removeFirst()}. |
408 |
|
* |
412 |
|
E remove(); |
413 |
|
|
414 |
|
/** |
415 |
< |
* Retrieves, but does not remove, the head of the queue represented by |
416 |
< |
* this deque, returning <tt>null</tt> if this deque is empty. |
415 |
> |
* Retrieves and removes the head of the queue represented by this deque |
416 |
> |
* (in other words, the first element of this deque), or returns |
417 |
> |
* {@code null} if this deque is empty. |
418 |
|
* |
419 |
< |
* <p>This method is equivalent to {@link #peekFirst()}. |
419 |
> |
* <p>This method is equivalent to {@link #pollFirst()}. |
420 |
|
* |
421 |
< |
* @return the head of the queue represented by this deque, or |
422 |
< |
* <tt>null</tt> if this deque is empty |
421 |
> |
* @return the first element of this deque, or {@code null} if |
422 |
> |
* this deque is empty |
423 |
|
*/ |
424 |
< |
E peek(); |
424 |
> |
E poll(); |
425 |
|
|
426 |
|
/** |
427 |
|
* Retrieves, but does not remove, the head of the queue represented by |
428 |
< |
* this deque. This method differs from the <tt>peek</tt> method only in |
429 |
< |
* that it throws an exception if this deque is empty. |
428 |
> |
* this deque (in other words, the first element of this deque). |
429 |
> |
* This method differs from {@link #peek peek} only in that it throws an |
430 |
> |
* exception if this deque is empty. |
431 |
|
* |
432 |
|
* <p>This method is equivalent to {@link #getFirst()}. |
433 |
|
* |
436 |
|
*/ |
437 |
|
E element(); |
438 |
|
|
439 |
+ |
/** |
440 |
+ |
* Retrieves, but does not remove, the head of the queue represented by |
441 |
+ |
* this deque (in other words, the first element of this deque), or |
442 |
+ |
* returns {@code null} if this deque is empty. |
443 |
+ |
* |
444 |
+ |
* <p>This method is equivalent to {@link #peekFirst()}. |
445 |
+ |
* |
446 |
+ |
* @return the head of the queue represented by this deque, or |
447 |
+ |
* {@code null} if this deque is empty |
448 |
+ |
*/ |
449 |
+ |
E peek(); |
450 |
+ |
|
451 |
|
|
452 |
|
// *** Stack methods *** |
453 |
|
|
454 |
|
/** |
455 |
< |
* Pushes an element onto the stack represented by this deque. In other |
456 |
< |
* words, inserts the element at the front of this deque unless it would |
457 |
< |
* violate capacity restrictions. |
455 |
> |
* Pushes an element onto the stack represented by this deque (in other |
456 |
> |
* words, at the head of this deque) if it is possible to do so |
457 |
> |
* immediately without violating capacity restrictions, throwing an |
458 |
> |
* {@code IllegalStateException} if no space is currently available. |
459 |
|
* |
460 |
|
* <p>This method is equivalent to {@link #addFirst}. |
461 |
|
* |
462 |
|
* @param e the element to push |
463 |
< |
* @throws IllegalStateException if it was not possible to insert |
464 |
< |
* the element due to capacity restrictions |
463 |
> |
* @throws IllegalStateException if the element cannot be added at this |
464 |
> |
* time due to capacity restrictions |
465 |
> |
* @throws ClassCastException if the class of the specified element |
466 |
> |
* prevents it from being added to this deque |
467 |
|
* @throws NullPointerException if the specified element is null and this |
468 |
< |
* deque does not permit null elements |
468 |
> |
* deque does not permit null elements |
469 |
> |
* @throws IllegalArgumentException if some property of the specified |
470 |
> |
* element prevents it from being added to this deque |
471 |
|
*/ |
472 |
|
void push(E e); |
473 |
|
|
478 |
|
* <p>This method is equivalent to {@link #removeFirst()}. |
479 |
|
* |
480 |
|
* @return the element at the front of this deque (which is the top |
481 |
< |
* of the stack represented by this deque) |
481 |
> |
* of the stack represented by this deque) |
482 |
|
* @throws NoSuchElementException if this deque is empty |
483 |
|
*/ |
484 |
|
E pop(); |
485 |
|
|
486 |
|
|
487 |
< |
// *** Collection Method *** |
487 |
> |
// *** Collection methods *** |
488 |
|
|
489 |
|
/** |
490 |
< |
* Returns an iterator over the elements in this deque. The elements |
491 |
< |
* will be ordered from first (head) to last (tail). |
490 |
> |
* Removes the first occurrence of the specified element from this deque. |
491 |
> |
* If the deque does not contain the element, it is unchanged. |
492 |
> |
* More formally, removes the first element {@code e} such that |
493 |
> |
* {@code Objects.equals(o, e)} (if such an element exists). |
494 |
> |
* Returns {@code true} if this deque contained the specified element |
495 |
> |
* (or equivalently, if this deque changed as a result of the call). |
496 |
> |
* |
497 |
> |
* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
498 |
|
* |
499 |
< |
* @return an <tt>Iterator</tt> over the elements in this deque |
499 |
> |
* @param o element to be removed from this deque, if present |
500 |
> |
* @return {@code true} if an element was removed as a result of this call |
501 |
> |
* @throws ClassCastException if the class of the specified element |
502 |
> |
* is incompatible with this deque |
503 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
504 |
> |
* @throws NullPointerException if the specified element is null and this |
505 |
> |
* deque does not permit null elements |
506 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
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 {@code Objects.equals(o, e)}. |
514 |
> |
* |
515 |
> |
* @param o element whose presence in this deque is to be tested |
516 |
> |
* @return {@code true} if this deque contains the specified element |
517 |
> |
* @throws ClassCastException if the class of the specified element |
518 |
> |
* is incompatible with this deque |
519 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
520 |
> |
* @throws NullPointerException if the specified element is null and this |
521 |
> |
* deque does not permit null elements |
522 |
> |
* (<a href="{@docRoot}/../api/java/util/Collection.html#optional-restrictions">optional</a>) |
523 |
> |
*/ |
524 |
> |
boolean contains(Object o); |
525 |
> |
|
526 |
> |
/** |
527 |
> |
* Returns the number of elements in this deque. |
528 |
> |
* |
529 |
> |
* @return the number of elements in this deque |
530 |
> |
*/ |
531 |
> |
int size(); |
532 |
> |
|
533 |
> |
/** |
534 |
> |
* Returns an iterator over the elements in this deque in proper sequence. |
535 |
> |
* The elements will be returned in order from first (head) to last (tail). |
536 |
> |
* |
537 |
> |
* @return an iterator over the elements in this deque in proper sequence |
538 |
|
*/ |
539 |
|
Iterator<E> iterator(); |
540 |
+ |
|
541 |
+ |
/** |
542 |
+ |
* Returns an iterator over the elements in this deque in reverse |
543 |
+ |
* sequential order. The elements will be returned in order from |
544 |
+ |
* last (tail) to first (head). |
545 |
+ |
* |
546 |
+ |
* @return an iterator over the elements in this deque in reverse |
547 |
+ |
* sequence |
548 |
+ |
*/ |
549 |
+ |
Iterator<E> descendingIterator(); |
550 |
+ |
|
551 |
|
} |