Interface - java.util.Deque

Created by : Mr Dk.

2019 / 11 / 12 0:28

Nanjing, Jiangsu, China

Definition

public interface Deque<E> extends Queue<E> {
}

线性集合，支持在两端插入和删除。Deque - "double ended queue" (pronounced deck)。大部分实现对集合容量没有特定限制，但也支持指定容量的双端队列。接口对队列两端都定义了以下几种操作：

  • insert
  • remove
  • examine
  • element

每种操作都有两种形式：

  • 操作失败后抛出异常
  • 操作失败后返回特定值 (null 或 false)
/**
 * 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 {@code Deque}
 * 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 {@code null} or {@code false}, depending on
 * the operation).  The latter form of the insert operation is
 * designed specifically for use with capacity-restricted
 * {@code Deque} implementations; in most implementations, insert
 * operations cannot fail.
 *
 * <p>The twelve methods described above are summarized in the
 * following table:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Summary of Deque methods</caption>
 *  <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 Deque#addFirst addFirst(e)}</td>
 *    <td>{@link Deque#offerFirst offerFirst(e)}</td>
 *    <td>{@link Deque#addLast addLast(e)}</td>
 *    <td>{@link Deque#offerLast offerLast(e)}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Remove</b></td>
 *    <td>{@link Deque#removeFirst removeFirst()}</td>
 *    <td>{@link Deque#pollFirst pollFirst()}</td>
 *    <td>{@link Deque#removeLast removeLast()}</td>
 *    <td>{@link Deque#pollLast pollLast()}</td>
 *  </tr>
 *  <tr>
 *    <td><b>Examine</b></td>
 *    <td>{@link Deque#getFirst getFirst()}</td>
 *    <td>{@link Deque#peekFirst peekFirst()}</td>
 *    <td>{@link Deque#getLast getLast()}</td>
 *    <td>{@link Deque#peekLast peekLast()}</td>
 *  </tr>
 * </table>
 *
 * <p>This interface extends the {@link 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 {@code Queue} interface are precisely equivalent to
 * {@code Deque} methods as indicated in the following table:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Comparison of Queue and Deque methods</caption>
 *  <tr>
 *    <td ALIGN=CENTER> <b>{@code Queue} Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent {@code Deque} 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 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
 * {@code Deque} methods as indicated in the table below:
 *
 * <table BORDER CELLPADDING=3 CELLSPACING=1>
 * <caption>Comparison of Stack and Deque methods</caption>
 *  <tr>
 *    <td ALIGN=CENTER> <b>Stack Method</b></td>
 *    <td ALIGN=CENTER> <b>Equivalent {@code Deque} 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 List} interface, this interface does not
 * provide support for indexed access to elements.
 *
 * <p>While {@code Deque} implementations are not strictly required
 * to prohibit the insertion of null elements, they are strongly
 * encouraged to do so.  Users of any {@code Deque} 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
 * {@code null} is used as a special return value by various methods
 * to indicated that the deque is empty.
 *
 * <p>{@code Deque} implementations generally do not define
 * element-based versions of the {@code equals} and {@code hashCode}
 * methods, but instead inherit the identity-based versions from class
 * {@code Object}.
 *
 * <p>This interface is a member of the <a
 * href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
 * Framework</a>.
 *
 * @author Doug Lea
 * @author Josh Bloch
 * @since  1.6
 * @param <E> the type of elements held in this collection
 */

插入操作

add 一族会在插入失败后抛出异常。

void addFirst(E e);
void addLast(E e);
boolean offerFirst(E e);
boolean offerLast(E e);

删除操作

remove 会在队列已经为空时抛出异常。

E removeFirst();
E removeLast();
E pollFirst();
E pollLast();

boolean removeFirstOccurrence(Object o);
boolean removeLastOccurrence(Object o);

访问操作

get 会在队列已经为空时抛出异常。

E getFirst();
E getLast();
E peekFirst();
E peekLast();

接口操作

双端队列在当做普通队列使用时，以下函数和普通队列的函数等价：数据从队尾加入，从队头删除。

  • java.util.Queue.add() - addLast()
  • java.util.Queue.offer() - offerLast()
  • java.util.Queue.remove() - removeFirst()
  • java.util.Queue.poll() - pollFirst()
  • java.util.Queue.element() - getFirst()
  • java.util.Queue.peek() - peekFirst()

双端队列当做栈使用时，以下函数等价：总在队头出栈、入栈。

  • push() - addFirst()
  • pop() - removeFirst()
  • peek() - peekFirst()

集合操作

集合操作依旧是那几个：

  • remove()
  • contains()
  • size()
  • iterator()
  • descendingIterator()