/*

 * 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);

}