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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
package java.util.concurrent;
import java.util.*;
 * A {@link Deque} that additionally supports blocking operations that wait
 * for the deque to become non-empty when retrieving an element, and wait for
 * space to become available in the deque when storing an element.
 * <p>{@code BlockingDeque} methods come in four forms, with different ways
 * of handling operations that cannot be satisfied immediately, but may be
 * satisfied at some point in the future:
 * one throws an exception, the second returns a special value (either
 * {@code null} or {@code false}, depending on the operation), the third
 * blocks the current thread indefinitely until the operation can succeed,
 * and the fourth blocks for only a given maximum time limit before giving
 * up.  These methods are summarized in the following table:
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Summary of BlockingDeque methods</caption>
 *    <td ALIGN=CENTER COLSPAN = 5> <b>First Element (Head)</b></td>
 *    <td></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Special value</em></td>
 *    <td ALIGN=CENTER><em>Blocks</em></td>
 *    <td ALIGN=CENTER><em>Times out</em></td>
 *    <td><b>Insert</b></td>
 *    <td>{@link #addFirst addFirst(e)}</td>
 *    <td>{@link #offerFirst(Object) offerFirst(e)}</td>
 *    <td>{@link #putFirst putFirst(e)}</td>
 *    <td>{@link #offerFirst(Object, long, TimeUnit) offerFirst(e, time, unit)}</td>
 *    <td><b>Remove</b></td>
 *    <td>{@link #removeFirst removeFirst()}</td>
 *    <td>{@link #pollFirst pollFirst()}</td>
 *    <td>{@link #takeFirst takeFirst()}</td>
 *    <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
 *    <td><b>Examine</b></td>
 *    <td>{@link #getFirst getFirst()}</td>
 *    <td>{@link #peekFirst peekFirst()}</td>
 *    <td><em>not applicable</em></td>
 *    <td><em>not applicable</em></td>
 *    <td ALIGN=CENTER COLSPAN = 5> <b>Last Element (Tail)</b></td>
 *    <td></td>
 *    <td ALIGN=CENTER><em>Throws exception</em></td>
 *    <td ALIGN=CENTER><em>Special value</em></td>
 *    <td ALIGN=CENTER><em>Blocks</em></td>
 *    <td ALIGN=CENTER><em>Times out</em></td>
 *    <td><b>Insert</b></td>
 *    <td>{@link #addLast addLast(e)}</td>
 *    <td>{@link #offerLast(Object) offerLast(e)}</td>
 *    <td>{@link #putLast putLast(e)}</td>
 *    <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
 *    <td><b>Remove</b></td>
 *    <td>{@link #removeLast() removeLast()}</td>
 *    <td>{@link #pollLast() pollLast()}</td>
 *    <td>{@link #takeLast takeLast()}</td>
 *    <td>{@link #pollLast(long, TimeUnit) pollLast(time, unit)}</td>
 *    <td><b>Examine</b></td>
 *    <td>{@link #getLast getLast()}</td>
 *    <td>{@link #peekLast peekLast()}</td>
 *    <td><em>not applicable</em></td>
 *    <td><em>not applicable</em></td>
 * </table>
 * <p>Like any {@link BlockingQueue}, a {@code BlockingDeque} is thread safe,
 * does not permit null elements, and may (or may not) be
 * capacity-constrained.
 * <p>A {@code BlockingDeque} implementation may be used directly as a FIFO
 * {@code BlockingQueue}. The methods inherited from the
 * {@code BlockingQueue} interface are precisely equivalent to
 * {@code BlockingDeque} methods as indicated in the following table:
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Comparison of BlockingQueue and BlockingDeque methods</caption>
 *    <td ALIGN=CENTER> <b>{@code BlockingQueue} Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent {@code BlockingDeque} Method</b></td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>Insert</b></td>
 *    <td>{@link #add(Object) add(e)}</td>
 *    <td>{@link #addLast(Object) addLast(e)}</td>
 *    <td>{@link #offer(Object) offer(e)}</td>
 *    <td>{@link #offerLast(Object) offerLast(e)}</td>
 *    <td>{@link #put(Object) put(e)}</td>
 *    <td>{@link #putLast(Object) putLast(e)}</td>
 *    <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
 *    <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>Remove</b></td>
 *    <td>{@link #remove() remove()}</td>
 *    <td>{@link #removeFirst() removeFirst()}</td>
 *    <td>{@link #poll() poll()}</td>
 *    <td>{@link #pollFirst() pollFirst()}</td>
 *    <td>{@link #take() take()}</td>
 *    <td>{@link #takeFirst() takeFirst()}</td>
 *    <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
 *    <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
 *    <td ALIGN=CENTER COLSPAN = 2> <b>Examine</b></td>
 *    <td>{@link #element() element()}</td>
 *    <td>{@link #getFirst() getFirst()}</td>
 *    <td>{@link #peek() peek()}</td>
 *    <td>{@link #peekFirst() peekFirst()}</td>
 * </table>
 * <p>Memory consistency effects: As with other concurrent
 * collections, actions in a thread prior to placing an object into a
 * {@code BlockingDeque}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions subsequent to the access or removal of that element from
 * the {@code BlockingDeque} in another thread.
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 * @since 1.6
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
public interface BlockingDeque<E> extends BlockingQueue<E>, Deque<E> {
     * We have "diamond" multiple interface inheritance here, and that
     * introduces ambiguities.  Methods might end up with different
     * specs depending on the branch chosen by javadoc.  Thus a lot of
     * methods specs here are copied from superinterfaces.
     * Inserts the specified element at the front of this deque if it is
     * possible to do so immediately without violating capacity restrictions,
     * throwing an {@code IllegalStateException} if no space is currently
     * available.  When using a capacity-restricted deque, it is generally
     * preferable to use {@link #offerFirst(Object) offerFirst}.
     * @param e the element to add
     * @throws IllegalStateException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException {@inheritDoc}
    void addFirst(E e);
     * Inserts the specified element at the end of this deque if it is
     * possible to do so immediately without violating capacity restrictions,
     * throwing an {@code IllegalStateException} if no space is currently
     * available.  When using a capacity-restricted deque, it is generally
     * preferable to use {@link #offerLast(Object) offerLast}.
     * @param e the element to add
     * @throws IllegalStateException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException {@inheritDoc}
    void addLast(E e);
     * Inserts the specified element at the front of this deque if it is
     * possible to do so immediately without violating capacity restrictions,
     * returning {@code true} upon success and {@code false} if no space is
     * currently available.
     * When using a capacity-restricted deque, this method is generally
     * preferable to the {@link #addFirst(Object) addFirst} method, which can
     * fail to insert an element only by throwing an exception.
     * @param e the element to add
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException {@inheritDoc}
    boolean offerFirst(E e);
     * Inserts the specified element at the end of this deque if it is
     * possible to do so immediately without violating capacity restrictions,
     * returning {@code true} upon success and {@code false} if no space is
     * currently available.
     * When using a capacity-restricted deque, this method is generally
     * preferable to the {@link #addLast(Object) addLast} method, which can
     * fail to insert an element only by throwing an exception.
     * @param e the element to add
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException {@inheritDoc}
    boolean offerLast(E e);
     * Inserts the specified element at the front of this deque,
     * waiting if necessary for space to become available.
     * @param e the element to add
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    void putFirst(E e) throws InterruptedException;
     * Inserts the specified element at the end of this deque,
     * waiting if necessary for space to become available.
     * @param e the element to add
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    void putLast(E e) throws InterruptedException;
     * Inserts the specified element at the front of this deque,
     * waiting up to the specified wait time if necessary for space to
     * become available.
     * @param e the element to add
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return {@code true} if successful, or {@code false} if
     *         the specified waiting time elapses before space is available
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    boolean offerFirst(E e, long timeout, TimeUnit unit)
        throws InterruptedException;
     * Inserts the specified element at the end of this deque,
     * waiting up to the specified wait time if necessary for space to
     * become available.
     * @param e the element to add
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return {@code true} if successful, or {@code false} if
     *         the specified waiting time elapses before space is available
     * @throws InterruptedException if interrupted while waiting
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    boolean offerLast(E e, long timeout, TimeUnit unit)
        throws InterruptedException;
     * Retrieves and removes the first element of this deque, waiting
     * if necessary until an element becomes available.
     * @return the head of this deque
     * @throws InterruptedException if interrupted while waiting
    E takeFirst() throws InterruptedException;
     * Retrieves and removes the last element of this deque, waiting
     * if necessary until an element becomes available.
     * @return the tail of this deque
     * @throws InterruptedException if interrupted while waiting
    E takeLast() throws InterruptedException;
     * Retrieves and removes the first element of this deque, waiting
     * up to the specified wait time if necessary for an element to
     * become available.
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return the head of this deque, or {@code null} if the specified
     *         waiting time elapses before an element is available
     * @throws InterruptedException if interrupted while waiting
    E pollFirst(long timeout, TimeUnit unit)
        throws InterruptedException;
     * Retrieves and removes the last element of this deque, waiting
     * up to the specified wait time if necessary for an element to
     * become available.
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return the tail of this deque, or {@code null} if the specified
     *         waiting time elapses before an element is available
     * @throws InterruptedException if interrupted while waiting
    E pollLast(long timeout, TimeUnit unit)
        throws InterruptedException;
     * Removes the first occurrence of the specified element from this deque.
     * If the deque does not contain the element, it is unchanged.
     * More formally, removes the first element {@code e} such that
     * {@code o.equals(e)} (if such an element exists).
     * Returns {@code true} if this deque contained the specified element
     * (or equivalently, if this deque changed as a result of the call).
     * @param o element to be removed from this deque, if present
     * @return {@code true} if an element was removed as a result of this call
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this deque
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
    boolean removeFirstOccurrence(Object o);
     * Removes the last occurrence of the specified element from this deque.
     * If the deque does not contain the element, it is unchanged.
     * More formally, removes the last element {@code e} such that
     * {@code o.equals(e)} (if such an element exists).
     * Returns {@code true} if this deque contained the specified element
     * (or equivalently, if this deque changed as a result of the call).
     * @param o element to be removed from this deque, if present
     * @return {@code true} if an element was removed as a result of this call
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this deque
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
    boolean removeLastOccurrence(Object o);
    // *** BlockingQueue methods ***
     * Inserts the specified element into the queue represented by this deque
     * (in other words, at the tail of this deque) if it is possible to do so
     * immediately without violating capacity restrictions, returning
     * {@code true} upon success and throwing an
     * {@code IllegalStateException} if no space is currently available.
     * When using a capacity-restricted deque, it is generally preferable to
     * use {@link #offer(Object) offer}.
     * <p>This method is equivalent to {@link #addLast(Object) addLast}.
     * @param e the element to add
     * @throws IllegalStateException {@inheritDoc}
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    boolean add(E e);
     * Inserts the specified element into the queue represented by this deque
     * (in other words, at the tail of this deque) if it is possible to do so
     * immediately without violating capacity restrictions, returning
     * {@code true} upon success and {@code false} if no space is currently
     * available.  When using a capacity-restricted deque, this method is
     * generally preferable to the {@link #add} method, which can fail to
     * insert an element only by throwing an exception.
     * <p>This method is equivalent to {@link #offerLast(Object) offerLast}.
     * @param e the element to add
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    boolean offer(E e);
     * Inserts the specified element into the queue represented by this deque
     * (in other words, at the tail of this deque), waiting if necessary for
     * space to become available.
     * <p>This method is equivalent to {@link #putLast(Object) putLast}.
     * @param e the element to add
     * @throws InterruptedException {@inheritDoc}
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    void put(E e) throws InterruptedException;
     * Inserts the specified element into the queue represented by this deque
     * (in other words, at the tail of this deque), waiting up to the
     * specified wait time if necessary for space to become available.
     * <p>This method is equivalent to
     * {@link #offerLast(Object,long,TimeUnit) offerLast}.
     * @param e the element to add
     * @return {@code true} if the element was added to this deque, else
     *         {@code false}
     * @throws InterruptedException {@inheritDoc}
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this deque
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this deque
    boolean offer(E e, long timeout, TimeUnit unit)
        throws InterruptedException;
     * Retrieves and removes the head of the queue represented by this deque
     * (in other words, the first element of this deque).
     * This method differs from {@link #poll poll} only in that it
     * throws an exception if this deque is empty.
     * <p>This method is equivalent to {@link #removeFirst() removeFirst}.
     * @return the head of the queue represented by this deque
     * @throws NoSuchElementException if this deque is empty
    E remove();
     * Retrieves and removes the head of the queue represented by this deque
     * (in other words, the first element of this deque), or returns
     * {@code null} if this deque is empty.
     * <p>This method is equivalent to {@link #pollFirst()}.
     * @return the head of this deque, or {@code null} if this deque is empty
    E poll();
     * Retrieves and removes the head of the queue represented by this deque
     * (in other words, the first element of this deque), waiting if
     * necessary until an element becomes available.
     * <p>This method is equivalent to {@link #takeFirst() takeFirst}.
     * @return the head of this deque
     * @throws InterruptedException if interrupted while waiting
    E take() throws InterruptedException;
     * Retrieves and removes the head of the queue represented by this deque
     * (in other words, the first element of this deque), waiting up to the
     * specified wait time if necessary for an element to become available.
     * <p>This method is equivalent to
     * {@link #pollFirst(long,TimeUnit) pollFirst}.
     * @return the head of this deque, or {@code null} if the
     *         specified waiting time elapses before an element is available
     * @throws InterruptedException if interrupted while waiting
    E poll(long timeout, TimeUnit unit)
        throws InterruptedException;
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque (in other words, the first element of this deque).
     * This method differs from {@link #peek peek} only in that it throws an
     * exception if this deque is empty.
     * <p>This method is equivalent to {@link #getFirst() getFirst}.
     * @return the head of this deque
     * @throws NoSuchElementException if this deque is empty
    E element();
     * Retrieves, but does not remove, the head of the queue represented by
     * this deque (in other words, the first element of this deque), or
     * returns {@code null} if this deque is empty.
     * <p>This method is equivalent to {@link #peekFirst() peekFirst}.
     * @return the head of this deque, or {@code null} if this deque is empty
    E peek();
     * Removes the first occurrence of the specified element from this deque.
     * If the deque does not contain the element, it is unchanged.
     * More formally, removes the first element {@code e} such that
     * {@code o.equals(e)} (if such an element exists).
     * Returns {@code true} if this deque contained the specified element
     * (or equivalently, if this deque changed as a result of the call).
     * <p>This method is equivalent to
     * {@link #removeFirstOccurrence(Object) removeFirstOccurrence}.
     * @param o element to be removed from this deque, if present
     * @return {@code true} if this deque changed as a result of the call
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this deque
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
    boolean remove(Object o);
     * Returns {@code true} if this deque contains the specified element.
     * More formally, returns {@code true} if and only if this deque contains
     * at least one element {@code e} such that {@code o.equals(e)}.
     * @param o object to be checked for containment in this deque
     * @return {@code true} if this deque contains the specified element
     * @throws ClassCastException if the class of the specified element
     *         is incompatible with this deque
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null
     *         (<a href="../Collection.html#optional-restrictions">optional</a>)
    public boolean contains(Object o);
     * Returns the number of elements in this deque.
     * @return the number of elements in this deque
    public int size();
     * Returns an iterator over the elements in this deque in proper sequence.
     * The elements will be returned in order from first (head) to last (tail).
     * @return an iterator over the elements in this deque in proper sequence
    Iterator<E> iterator();
    // *** Stack methods ***
     * Pushes an element onto the stack represented by this deque (in other
     * words, at the head of this deque) if it is possible to do so
     * immediately without violating capacity restrictions, throwing an
     * {@code IllegalStateException} if no space is currently available.
     * <p>This method is equivalent to {@link #addFirst(Object) addFirst}.
     * @throws IllegalStateException {@inheritDoc}
     * @throws ClassCastException {@inheritDoc}
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException {@inheritDoc}
    void push(E e);
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