/*

  * 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.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.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/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><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

      *         (<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 <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

      *         (<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

      * <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

      *         (<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 <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

      *         (<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, 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);

 }