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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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* <table class="striped"> |
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* <caption>Summary of Deque methods</caption> |
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* <thead> |
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* <tr> |
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* <td rowspan="2"></td> |
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* <th scope="col" colspan="2"> First Element (Head)</th> |
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* <th scope="col" colspan="2"> Last Element (Tail)</th> |
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* </tr> |
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* <tr> |
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* <th scope="col" style="font-weight:normal; font-style:italic">Throws exception</th> |
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* <th scope="col" style="font-weight:normal; font-style:italic">Special value</th> |
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* <th scope="col" style="font-weight:normal; font-style:italic">Throws exception</th> |
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* <th scope="col" style="font-weight:normal; font-style:italic">Special value</th> |
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* </tr> |
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* </thead> |
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* <tbody> |
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* <tr> |
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* <th scope="row">Insert</th> |
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* <td>{@link #addFirst(Object) addFirst(e)}</td> |
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* <td>{@link #offerFirst(Object) offerFirst(e)}</td> |
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* <td>{@link #addLast(Object) addLast(e)}</td> |
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* <td>{@link #offerLast(Object) offerLast(e)}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">Remove</th> |
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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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* </tr> |
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* <tr> |
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* <th scope="row">Examine</th> |
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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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* </tr> |
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* </tbody> |
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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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* <table class="striped"> |
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* <caption>Comparison of Queue and Deque methods</caption> |
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* <thead> |
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* <tr> |
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* <th scope="col"> {@code Queue} Method</th> |
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* <th scope="col"> Equivalent {@code Deque} Method</th> |
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* </tr> |
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* </thead> |
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* <tbody> |
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* <tr> |
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* <th scope="row">{@link #add(Object) add(e)}</th> |
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* <td>{@link #addLast(Object) addLast(e)}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #offer(Object) offer(e)}</th> |
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* <td>{@link #offerLast(Object) offerLast(e)}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #remove() remove()}</th> |
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* <td>{@link #removeFirst() removeFirst()}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #poll() poll()}</th> |
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* <td>{@link #pollFirst() pollFirst()}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #element() element()}</th> |
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* <td>{@link #getFirst() getFirst()}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #peek() peek()}</th> |
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* <td>{@link #peekFirst() peekFirst()}</td> |
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* </tr> |
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* </tbody> |
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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 equivalent to {@code Deque} |
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* methods as indicated in the table below: |
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* |
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* <table class="striped"> |
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* <caption>Comparison of Stack and Deque methods</caption> |
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* <thead> |
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* <tr> |
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* <th scope="col"> Stack Method</th> |
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* <th scope="col"> Equivalent {@code Deque} Method</th> |
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* </tr> |
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* </thead> |
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* <tbody> |
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* <tr> |
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* <th scope="row">{@link #push(Object) push(e)}</th> |
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* <td>{@link #addFirst(Object) addFirst(e)}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #pop() pop()}</th> |
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* <td>{@link #removeFirst() removeFirst()}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row">{@link #peek() peek()}</th> |
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* <td>{@link #getFirst() getFirst()}</td> |
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* </tr> |
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* </tbody> |
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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 indicate 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 |
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* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> |
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* Java Collections 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 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 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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* {@code Objects.equals(o, e)} (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 |
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* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
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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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* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
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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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* {@code Objects.equals(o, e)} (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 |
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* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
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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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* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
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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 |
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* generally preferable to the {@link #add} method, which can fail to |
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* insert an element only by throwing an exception. |
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* |
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* <p>This method is equivalent to {@link #offerLast}. |
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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 offer(E e); |
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|
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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). |
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* This method differs from {@link #poll() poll()} only in that it |
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* throws an exception if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #removeFirst()}. |
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* |
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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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/** |
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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), or returns |
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* {@code null} if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #pollFirst()}. |
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* |
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* @return the first element of this deque, or {@code null} if |
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* this deque is empty |
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*/ |
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E poll(); |
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|
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/** |
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* Retrieves, but does not remove, the head of the queue represented by |
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* this deque (in other words, the first element of this deque). |
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* This method differs from {@link #peek peek} only in that it throws an |
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* exception if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #getFirst()}. |
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* |
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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 element(); |
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|
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/** |
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* Retrieves, but does not remove, the head of the queue represented by |
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* this deque (in other words, the first element of this deque), or |
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* returns {@code null} if this deque is empty. |
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* |
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* <p>This method is equivalent to {@link #peekFirst()}. |
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* |
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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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*/ |
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E peek(); |
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|
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/** |
463 |
* Adds all of the elements in the specified collection at the end |
464 |
* of this deque, as if by calling {@link #addLast} on each one, |
465 |
* in the order that they are returned by the collection's iterator. |
466 |
* |
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* <p>When using a capacity-restricted deque, it is generally preferable |
468 |
* to call {@link #offer(Object) offer} separately on each element. |
469 |
* |
470 |
* <p>An exception encountered while trying to add an element may result |
471 |
* in only some of the elements having been successfully added when |
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* the associated exception is thrown. |
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* |
474 |
* @param c the elements to be inserted into this deque |
475 |
* @return {@code true} if this deque changed as a result of the call |
476 |
* @throws IllegalStateException if not all the elements can be added at |
477 |
* this time due to insertion restrictions |
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* @throws ClassCastException if the class of an element of the specified |
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* collection prevents it from being added to this deque |
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* @throws NullPointerException if the specified collection contains a |
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* null element and this deque does not permit null elements, |
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* or if the specified collection is null |
483 |
* @throws IllegalArgumentException if some property of an element of the |
484 |
* specified collection prevents it from being added to this deque |
485 |
*/ |
486 |
boolean addAll(Collection<? extends E> c); |
487 |
|
488 |
// *** Stack methods *** |
489 |
|
490 |
/** |
491 |
* Pushes an element onto the stack represented by this deque (in other |
492 |
* words, at the head of this deque) if it is possible to do so |
493 |
* immediately without violating capacity restrictions, throwing an |
494 |
* {@code IllegalStateException} if no space is currently available. |
495 |
* |
496 |
* <p>This method is equivalent to {@link #addFirst}. |
497 |
* |
498 |
* @param e the element to push |
499 |
* @throws IllegalStateException if the element cannot be added at this |
500 |
* time due to capacity restrictions |
501 |
* @throws ClassCastException if the class of the specified element |
502 |
* prevents it from being added to this deque |
503 |
* @throws NullPointerException if the specified element is null and this |
504 |
* deque does not permit null elements |
505 |
* @throws IllegalArgumentException if some property of the specified |
506 |
* element prevents it from being added to this deque |
507 |
*/ |
508 |
void push(E e); |
509 |
|
510 |
/** |
511 |
* Pops an element from the stack represented by this deque. In other |
512 |
* words, removes and returns the first element of this deque. |
513 |
* |
514 |
* <p>This method is equivalent to {@link #removeFirst()}. |
515 |
* |
516 |
* @return the element at the front of this deque (which is the top |
517 |
* of the stack represented by this deque) |
518 |
* @throws NoSuchElementException if this deque is empty |
519 |
*/ |
520 |
E pop(); |
521 |
|
522 |
|
523 |
// *** Collection methods *** |
524 |
|
525 |
/** |
526 |
* Removes the first occurrence of the specified element from this deque. |
527 |
* If the deque does not contain the element, it is unchanged. |
528 |
* More formally, removes the first element {@code e} such that |
529 |
* {@code Objects.equals(o, e)} (if such an element exists). |
530 |
* Returns {@code true} if this deque contained the specified element |
531 |
* (or equivalently, if this deque changed as a result of the call). |
532 |
* |
533 |
* <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. |
534 |
* |
535 |
* @param o element to be removed from this deque, if present |
536 |
* @return {@code true} if an element was removed as a result of this call |
537 |
* @throws ClassCastException if the class of the specified element |
538 |
* is incompatible with this deque |
539 |
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
540 |
* @throws NullPointerException if the specified element is null and this |
541 |
* deque does not permit null elements |
542 |
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
543 |
*/ |
544 |
boolean remove(Object o); |
545 |
|
546 |
/** |
547 |
* Returns {@code true} if this deque contains the specified element. |
548 |
* More formally, returns {@code true} if and only if this deque contains |
549 |
* at least one element {@code e} such that {@code Objects.equals(o, e)}. |
550 |
* |
551 |
* @param o element whose presence in this deque is to be tested |
552 |
* @return {@code true} if this deque contains the specified element |
553 |
* @throws ClassCastException if the class of the specified element |
554 |
* is incompatible with this deque |
555 |
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
556 |
* @throws NullPointerException if the specified element is null and this |
557 |
* deque does not permit null elements |
558 |
* (<a href="{@docRoot}/java.base/java/util/Collection.html#optional-restrictions">optional</a>) |
559 |
*/ |
560 |
boolean contains(Object o); |
561 |
|
562 |
/** |
563 |
* Returns the number of elements in this deque. |
564 |
* |
565 |
* @return the number of elements in this deque |
566 |
*/ |
567 |
int size(); |
568 |
|
569 |
/** |
570 |
* Returns an iterator over the elements in this deque in proper sequence. |
571 |
* The elements will be returned in order from first (head) to last (tail). |
572 |
* |
573 |
* @return an iterator over the elements in this deque in proper sequence |
574 |
*/ |
575 |
Iterator<E> iterator(); |
576 |
|
577 |
/** |
578 |
* Returns an iterator over the elements in this deque in reverse |
579 |
* sequential order. The elements will be returned in order from |
580 |
* last (tail) to first (head). |
581 |
* |
582 |
* @return an iterator over the elements in this deque in reverse |
583 |
* sequence |
584 |
*/ |
585 |
Iterator<E> descendingIterator(); |
586 |
|
587 |
} |