content: /*
   * Written by Doug Lea and Josh Bloch 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 com.zzxhdzj.http.asynctask;
  
  import java.util.Iterator;
  import java.util.Queue;
  
  // BEGIN android-note
  // removed link to collections framework docs
  // END android-note
  
  /**
   * A linear collection that supports element insertion and removal at
   * both ends.  The name <i>deque</i> is short for "double ended queue"
   * and is usually pronounced "deck".  Most <tt>Deque</tt>
   * implementations place no fixed limits on the number of elements
   * they may contain, but this interface supports capacity-restricted
   * deques as well as those with no fixed size limit.
   *
   * <p>This interface defines methods to access the elements at both
   * ends of the deque.  Methods are provided to insert, remove, and
   * examine the element.  Each of these methods exists in two forms:
   * one throws an exception if the operation fails, the other returns a
   * special value (either <tt>null</tt> or <tt>false</tt>, depending on
   * the operation).  The latter form of the insert operation is
   * designed specifically for use with capacity-restricted
   * <tt>Deque</tt> implementations; in most implementations, insert
   * operations cannot fail.
   *
   * <p>The twelve methods described above are summarized in the
   * following table:
   *
   * <p>
   * <table BORDER CELLPADDING=3 CELLSPACING=1>
   *  <tr>
   *    <td></td>
   *    <td ALIGN=CENTER COLSPAN = 2> <b>First Element (Head)</b></td>
   *    <td ALIGN=CENTER COLSPAN = 2> <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>Throws exception</em></td>
   *    <td ALIGN=CENTER><em>Special value</em></td>
   *  </tr>
   *  <tr>
   *    <td><b>Insert</b></td>
   *    <td>{@link #addFirst addFirst(e)}</td>
   *    <td>{@link #offerFirst offerFirst(e)}</td>
   *    <td>{@link #addLast addLast(e)}</td>
   *    <td>{@link #offerLast offerLast(e)}</td>
   *  </tr>
   *  <tr>
   *    <td><b>Remove</b></td>
   *    <td>{@link #removeFirst removeFirst()}</td>
   *    <td>{@link #pollFirst pollFirst()}</td>
   *    <td>{@link #removeLast removeLast()}</td>
   *    <td>{@link #pollLast pollLast()}</td>
   *  </tr>
   *  <tr>
   *    <td><b>Examine</b></td>
   *    <td>{@link #getFirst getFirst()}</td>
   *    <td>{@link #peekFirst peekFirst()}</td>
   *    <td>{@link #getLast getLast()}</td>
   *    <td>{@link #peekLast peekLast()}</td>
   *  </tr>
   * </table>
   *
   * <p>This interface extends the {@link java.util.Queue} interface.  When a deque is
   * used as a queue, FIFO (First-In-First-Out) behavior results.  Elements are
   * added at the end of the deque and removed from the beginning.  The methods
   * inherited from the <tt>Queue</tt> interface are precisely equivalent to
   * <tt>Deque</tt> methods as indicated in the following table:
   *
   * <p>
   * <table BORDER CELLPADDING=3 CELLSPACING=1>
   *  <tr>
   *    <td ALIGN=CENTER> <b><tt>Queue</tt> Method</b></td>
   *    <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
   *  </tr>
   *  <tr>
   *    <td>{@link java.util.Queue#add add(e)}</td>
   *    <td>{@link #addLast addLast(e)}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link java.util.Queue#offer offer(e)}</td>
   *    <td>{@link #offerLast offerLast(e)}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link java.util.Queue#remove remove()}</td>
   *    <td>{@link #removeFirst removeFirst()}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link java.util.Queue#poll poll()}</td>
   *    <td>{@link #pollFirst pollFirst()}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link java.util.Queue#element element()}</td>
   *    <td>{@link #getFirst getFirst()}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link java.util.Queue#peek peek()}</td>
   *    <td>{@link #peek peekFirst()}</td>
   *  </tr>
   * </table>
   *
   * <p>Deques can also be used as LIFO (Last-In-First-Out) stacks.  This
   * interface should be used in preference to the legacy {@link java.util.Stack} class.
   * When a deque is used as a stack, elements are pushed and popped from the
   * beginning of the deque.  Stack methods are precisely equivalent to
   * <tt>Deque</tt> methods as indicated in the table below:
   *
   * <p>
   * <table BORDER CELLPADDING=3 CELLSPACING=1>
   *  <tr>
   *    <td ALIGN=CENTER> <b>Stack Method</b></td>
   *    <td ALIGN=CENTER> <b>Equivalent <tt>Deque</tt> Method</b></td>
   *  </tr>
   *  <tr>
   *    <td>{@link #push push(e)}</td>
   *    <td>{@link #addFirst addFirst(e)}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link #pop pop()}</td>
   *    <td>{@link #removeFirst removeFirst()}</td>
   *  </tr>
   *  <tr>
   *    <td>{@link #peek peek()}</td>
   *    <td>{@link #peekFirst peekFirst()}</td>
   *  </tr>
   * </table>
   *
   * <p>Note that the {@link #peek peek} method works equally well when
   * a deque is used as a queue or a stack; in either case, elements are
   * drawn from the beginning of the deque.
   *
   * <p>This interface provides two methods to remove interior
   * elements, {@link #removeFirstOccurrence removeFirstOccurrence} and
   * {@link #removeLastOccurrence removeLastOccurrence}.
   *
   * <p>Unlike the {@link java.util.List} interface, this interface does not
   * provide support for indexed access to elements.
   *
   * <p>While <tt>Deque</tt> implementations are not strictly required
   * to prohibit the insertion of null elements, they are strongly
   * encouraged to do so.  Users of any <tt>Deque</tt> implementations
   * that do allow null elements are strongly encouraged <i>not</i> to
   * take advantage of the ability to insert nulls.  This is so because
   * <tt>null</tt> is used as a special return value by various methods
   * to indicated that the deque is empty.
   *
   * <p><tt>Deque</tt> implementations generally do not define
   * element-based versions of the <tt>equals</tt> and <tt>hashCode</tt>
   * methods, but instead inherit the identity-based versions from class
   * <tt>Object</tt>.
   *
   * @author Doug Lea
   * @author Josh Bloch
   * @since  1.6
   * @param <E> the type of elements held in this collection
   */
  
  public interface Deque<E> extends Queue<E> {
      /**
       * Inserts the specified element at the front of this deque if it is
       * possible to do so immediately without violating capacity restrictions.
       * When using a capacity-restricted deque, it is generally preferable to
       * use method {@link #offerFirst}.
       *
       * @param e the element to add
       * @throws IllegalStateException if the element cannot be added at this
       *         time due to capacity restrictions
       * @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 and this
       *         deque does not permit null elements
       * @throws IllegalArgumentException if some property of the specified
       *         element prevents it from being added to this deque
       */
      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.
       * When using a capacity-restricted deque, it is generally preferable to
       * use method {@link #offerLast}.
       *
       * <p>This method is equivalent to {@link #add}.
       *
       * @param e the element to add
       * @throws IllegalStateException if the element cannot be added at this
       *         time due to capacity restrictions
       * @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 and this
       *         deque does not permit null elements
       * @throws IllegalArgumentException if some property of the specified
       *         element prevents it from being added to this deque
       */
      void addLast(E e);
  
      /**
       * Inserts the specified element at the front of this deque unless it would
       * violate capacity restrictions.  When using a capacity-restricted deque,
       * this method is generally preferable to the {@link #addFirst} method,
       * which can fail to insert an element only by throwing an exception.
       *
       * @param e the element to add
       * @return <tt>true</tt> if the element was added to this deque, else
       *         <tt>false</tt>
       * @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 and this
       *         deque does not permit null elements
       * @throws IllegalArgumentException if some property of the specified
       *         element prevents it from being added to this deque
       */
      boolean offerFirst(E e);
  
      /**
       * Inserts the specified element at the end of this deque unless it would
       * violate capacity restrictions.  When using a capacity-restricted deque,
       * this method is generally preferable to the {@link #addLast} method,
       * which can fail to insert an element only by throwing an exception.
       *
       * @param e the element to add
       * @return <tt>true</tt> if the element was added to this deque, else
       *         <tt>false</tt>
       * @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 and this
       *         deque does not permit null elements
       * @throws IllegalArgumentException if some property of the specified
       *         element prevents it from being added to this deque
       */
      boolean offerLast(E e);
  
      /**
       * Retrieves and removes the first element of this deque.  This method
       * differs from {@link #pollFirst pollFirst} only in that it throws an
       * exception if this deque is empty.
       *
       * @return the head of this deque
       * @throws java.util.NoSuchElementException if this deque is empty
       */
      E removeFirst();
  
      /**
       * Retrieves and removes the last element of this deque.  This method
       * differs from {@link #pollLast pollLast} only in that it throws an
       * exception if this deque is empty.
       *
       * @return the tail of this deque
       * @throws java.util.NoSuchElementException if this deque is empty
       */
      E removeLast();
  
      /**
       * Retrieves and removes the first element of this deque,
       * or returns <tt>null</tt> if this deque is empty.
       *
       * @return the head of this deque, or <tt>null</tt> if this deque is empty
       */
      E pollFirst();
  
      /**
       * Retrieves and removes the last element of this deque,
       * or returns <tt>null</tt> if this deque is empty.
       *
       * @return the tail of this deque, or <tt>null</tt> if this deque is empty
       */
      E pollLast();
  
      /**
       * Retrieves, but does not remove, the first element of this deque.
       *
       * This method differs from {@link #peekFirst peekFirst} only in that it
       * throws an exception if this deque is empty.
       *
       * @return the head of this deque
       * @throws java.util.NoSuchElementException if this deque is empty
       */
      E getFirst();
  
      /**
       * Retrieves, but does not remove, the last element of this deque.
       * This method differs from {@link #peekLast peekLast} only in that it
       * throws an exception if this deque is empty.
       *
       * @return the tail of this deque
       * @throws java.util.NoSuchElementException if this deque is empty
       */
      E getLast();
  
      /**
       * Retrieves, but does not remove, the first element of this deque,
       * or returns <tt>null</tt> if this deque is empty.
       *
       * @return the head of this deque, or <tt>null</tt> if this deque is empty
       */
      E peekFirst();
  
      /**
       * Retrieves, but does not remove, the last element of this deque,
       * or returns <tt>null</tt> if this deque is empty.
       *
       * @return the tail of this deque, or <tt>null</tt> if this deque is empty
       */
      E peekLast();
  
      /**
       * 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==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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 and this
       *         deque does not permit null elements (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==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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 and this
       *         deque does not permit null elements (optional)
       */
      boolean removeLastOccurrence(Object o);
  
      // *** Queue 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}.
       *
       * @param e the element to add
       * @return <tt>true</tt> (as specified by {@link java.util.Collection#add})
       * @throws IllegalStateException if the element cannot be added at this
       *         time due to capacity restrictions
       * @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 and this
       *         deque does not permit null elements
       * @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}.
       *
       * @param e the element to add
       * @return <tt>true</tt> if the element was added to this deque, else
       *         <tt>false</tt>
       * @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 and this
       *         deque does not permit null elements
       * @throws IllegalArgumentException if some property of the specified
       *         element prevents it from being added to this deque
       */
      boolean offer(E e);
  
      /**
       * 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()}.
       *
       * @return the head of the queue represented by this deque
       * @throws java.util.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 first element of this deque, or <tt>null</tt> if
       *         this deque is empty
       */
      E poll();
  
      /**
       * 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()}.
       *
       * @return the head of the queue represented by this deque
       * @throws java.util.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()}.
       *
       * @return the head of the queue represented by this deque, or
       *         <tt>null</tt> if this deque is empty
       */
      E peek();
  
  
      // *** 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, returning
       * <tt>true</tt> upon success and throwing an
       * <tt>IllegalStateException</tt> if no space is currently available.
       *
       * <p>This method is equivalent to {@link #addFirst}.
       *
       * @param e the element to push
       * @throws IllegalStateException if the element cannot be added at this
       *         time due to capacity restrictions
       * @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 and this
       *         deque does not permit null elements
       * @throws IllegalArgumentException if some property of the specified
       *         element prevents it from being added to this deque
       */
      void push(E e);
  
      /**
       * Pops an element from the stack represented by this deque.  In other
       * words, removes and returns the first element of this deque.
       *
       * <p>This method is equivalent to {@link #removeFirst()}.
       *
       * @return the element at the front of this deque (which is the top
       *         of the stack represented by this deque)
       * @throws java.util.NoSuchElementException if this deque is empty
       */
      E pop();
  
  
      // *** Collection methods ***
  
      /**
       * 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==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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}.
       *
       * @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 and this
       *         deque does not permit null elements (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==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
       *
       * @param o element whose presence in this deque is to be tested
       * @return <tt>true</tt> if this deque contains the specified element
       * @throws ClassCastException if the type of the specified element
       *         is incompatible with this deque (optional)
       * @throws NullPointerException if the specified element is null and this
       *         deque does not permit null elements (optional)
       */
      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();
  
      /**
       * Returns an iterator over the elements in this deque in reverse
       * sequential order.  The elements will be returned in order from
       * last (tail) to first (head).
       *
       * @return an iterator over the elements in this deque in reverse
       * sequence
       */
      Iterator<E> descendingIterator();
  
  }
  