--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/util/concurrent/BlockingDeque.java Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,642 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * 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/licenses/publicdomain
+ */
+
+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><tt>BlockingDeque</tt> 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
+ * <tt>null</tt> or <tt>false</tt>, 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:
+ *
+ * <p>
+ * <table BORDER CELLPADDING=3 CELLSPACING=1>
+ * <tr>
+ * <td ALIGN=CENTER COLSPAN = 5> <b>First Element (Head)</b></td>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <td ALIGN=CENTER COLSPAN = 5> <b>Last Element (Tail)</b></td>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * <tr>
+ * <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>
+ * </tr>
+ * </table>
+ *
+ * <p>Like any {@link BlockingQueue}, a <tt>BlockingDeque</tt> is thread safe,
+ * does not permit null elements, and may (or may not) be
+ * capacity-constrained.
+ *
+ * <p>A <tt>BlockingDeque</tt> implementation may be used directly as a FIFO
+ * <tt>BlockingQueue</tt>. The methods inherited from the
+ * <tt>BlockingQueue</tt> interface are precisely equivalent to
+ * <tt>BlockingDeque</tt> methods as indicated in the following table:
+ *
+ * <p>
+ * <table BORDER CELLPADDING=3 CELLSPACING=1>
+ * <tr>
+ * <td ALIGN=CENTER> <b><tt>BlockingQueue</tt> Method</b></td>
+ * <td ALIGN=CENTER> <b>Equivalent <tt>BlockingDeque</tt> Method</b></td>
+ * </tr>
+ * <tr>
+ * <td ALIGN=CENTER COLSPAN = 2> <b>Insert</b></td>
+ * </tr>
+ * <tr>
+ * <td>{@link #add(Object) add(e)}</td>
+ * <td>{@link #addLast(Object) addLast(e)}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #offer(Object) offer(e)}</td>
+ * <td>{@link #offerLast(Object) offerLast(e)}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #put(Object) put(e)}</td>
+ * <td>{@link #putLast(Object) putLast(e)}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
+ * <td>{@link #offerLast(Object, long, TimeUnit) offerLast(e, time, unit)}</td>
+ * </tr>
+ * <tr>
+ * <td ALIGN=CENTER COLSPAN = 2> <b>Remove</b></td>
+ * </tr>
+ * <tr>
+ * <td>{@link #remove() remove()}</td>
+ * <td>{@link #removeFirst() removeFirst()}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #poll() poll()}</td>
+ * <td>{@link #pollFirst() pollFirst()}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #take() take()}</td>
+ * <td>{@link #takeFirst() takeFirst()}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
+ * <td>{@link #pollFirst(long, TimeUnit) pollFirst(time, unit)}</td>
+ * </tr>
+ * <tr>
+ * <td ALIGN=CENTER COLSPAN = 2> <b>Examine</b></td>
+ * </tr>
+ * <tr>
+ * <td>{@link #element() element()}</td>
+ * <td>{@link #getFirst() getFirst()}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link #peek() peek()}</td>
+ * <td>{@link #peekFirst() peekFirst()}</td>
+ * </tr>
+ * </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 <tt>IllegalStateException</tt> 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 <tt>IllegalStateException</tt> 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 <tt>true</tt> upon success and <tt>false</tt> 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 <tt>true</tt> upon success and <tt>false</tt> 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
+ * <tt>unit</tt>
+ * @param unit a <tt>TimeUnit</tt> determining how to interpret the
+ * <tt>timeout</tt> parameter
+ * @return <tt>true</tt> if successful, or <tt>false</tt> 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
+ * <tt>unit</tt>
+ * @param unit a <tt>TimeUnit</tt> determining how to interpret the
+ * <tt>timeout</tt> parameter
+ * @return <tt>true</tt> if successful, or <tt>false</tt> 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
+ * <tt>unit</tt>
+ * @param unit a <tt>TimeUnit</tt> determining how to interpret the
+ * <tt>timeout</tt> parameter
+ * @return the head of this deque, or <tt>null</tt> 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
+ * <tt>unit</tt>
+ * @param unit a <tt>TimeUnit</tt> determining how to interpret the
+ * <tt>timeout</tt> parameter
+ * @return the tail of this deque, or <tt>null</tt> 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 <tt>e</tt> such that
+ * <tt>o.equals(e)</tt> (if such an element exists).
+ * Returns <tt>true</tt> 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 <tt>true</tt> 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 (optional)
+ * @throws NullPointerException if the specified element is null (optional)
+ */
+ 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 <tt>e</tt> such that
+ * <tt>o.equals(e)</tt> (if such an element exists).
+ * Returns <tt>true</tt> 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 <tt>true</tt> 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 (optional)
+ * @throws NullPointerException if the specified element is null (optional)
+ */
+ 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
+ * <tt>true</tt> upon success and throwing an
+ * <tt>IllegalStateException</tt> 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
+ * <tt>true</tt> upon success and <tt>false</tt> 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 <tt>true</tt> if the element was added to this deque, else
+ * <tt>false</tt>
+ * @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
+ * <tt>null</tt> if this deque is empty.
+ *
+ * <p>This method is equivalent to {@link #pollFirst()}.
+ *
+ * @return the head of this deque, or <tt>null</tt> 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 <tt>null</tt> 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 <tt>null</tt> if this deque is empty.
+ *
+ * <p>This method is equivalent to {@link #peekFirst() peekFirst}.
+ *
+ * @return the head of this deque, or <tt>null</tt> 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 <tt>e</tt> such that
+ * <tt>o.equals(e)</tt> (if such an element exists).
+ * Returns <tt>true</tt> 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 <tt>true</tt> if this deque changed as a result of the call
+ * @throws ClassCastException if the class of the specified element
+ * is incompatible with this deque (optional)
+ * @throws NullPointerException if the specified element is null (optional)
+ */
+ boolean remove(Object o);
+
+ /**
+ * Returns <tt>true</tt> if this deque contains the specified element.
+ * More formally, returns <tt>true</tt> if and only if this deque contains
+ * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
+ *
+ * @param o object to be checked for containment in this deque
+ * @return <tt>true</tt> if this deque contains the specified element
+ * @throws ClassCastException if the class of the specified element
+ * is incompatible with this deque (optional)
+ * @throws NullPointerException if the specified element is null (optional)
+ */
+ 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, inserts the element at the front of this deque unless it would
+ * violate capacity restrictions.
+ *
+ * <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);
+}