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源码
package java.util;
/**
* 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
*/
public interface Deque<E> extends Queue<E> {
}
注释内容
-
支持在两端插入和移除线性集合
-
deque 是 “double ended queue”的缩写，并且它通常读作 “deck”
-
大多数 Deque 实现 限制它们可能包含的元素的数量
-
但是这个接口支持容量受限的和没有限制大小的 deque
-
这个接口定义访问 deque 两端元素的方法，提供插入、移除和检查元素的方法。这些方法都有两种形式：一种是如果操作失败抛出异常，另一种是返回一个特殊值（null 或者 false，取决于操作），后一种形式的插入操作是专门设计用于容量受限的队列实现；在大多数实现，插入操作不能失败
| First Element (Head) | Last Element (Tail) | |||
|---|---|---|---|---|
| Throws exception | Special value | Throws exception | Special value | |
| Insert | addFirst(e) | offerFirst(e) | addLast(e) | offerLast(e) |
| Remove | removeFirst() | pollFirst() | removeLast() | pollLast() |
| Examine | getFirst() | peekFirst() | getLast() | peekLast() |
- 这个接口扩展 Queue 接口，当 deque 用作队列，FIFO（First-In-First-Out）行为结果，元素被添加到 deque 的队尾并且从开始移除，从 Queue 接口继承的方法和 Deque 下表表示的方法等效
| Queue Method | Equivalent Deque Method |
|---|---|
| add(e) | addLast(e) |
| offer(e) | offerLast(e) |
| remove() | removeFirst() |
| poll() | pollFirst() |
| element() | getFirst() |
| peek() | peekFirst() |
- Deque 同样可以作为 LIFO（Last-In-First-Out）栈，这个接口应该优先于旧的 Stack 类，当 deque 被用作栈，元素从 deque 的开头被推入或弹出，Stack 方法和 Deque 方法等效
| Stack Method | Equivalent Deque Method |
|---|---|
| push(e) | addFirst(e) |
| pop() | removeFirst() |
| peek() | peekFirst() |
- 请注意，当 deque 被用作队列或者栈时，peek 方法同样有效，无论任何情况，元素都从 deque 的开头提取
- 这个接口提供两个方法同移除内部元素，
removeFirstOccurrence和removeLastOccurrence - List 接口接口不同，这个接口没有提供索引访问元素的支持
- 当 Deque 实现没有严格要求禁止插入 null 元素，它们强烈鼓励这样做。强烈建议任何允许 null 元素的 Deque 实现的用户不使用插入 null 的能力。这是因为 null 被各种方法用于特殊返回值，表明这个 deque 是空
- Deque 实现通常没有定义基于元素版本的 equals 和 hashCode 方法，而是从 Object 类继承基于身份的版本
