为什么java链表实现使用接口deque？
我在查看LinkedList的java实现，发现了这个：
public class LinkedList<E>
extends AbstractSequentialList<E> implements List<E>,
Deque<E>, Cloneable, java.io.Serializable
Why should a LinkedList support the Deque interface? 我理解将元素添加到链表末尾的愿望，但这些方法应该包含在 List 接口中。
I was looking at the java implementation of LinkedList, and found this:
public class LinkedList<E>
extends AbstractSequentialList<E> implements List<E>,
Deque<E>, Cloneable, java.io.Serializable
Why should a LinkedList support the Deque interface?
I understand the desire to add elements to the end of the linked list, but those methods should have been incuded in the List interface.
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LinkedList实现恰好满足Deque契约，那么为什么不让它实现该接口呢？The
LinkedListimplementation happens to to satisfy theDequecontract, so why not make it implement the interface?正如 JavaDocs 中所述：
这些操作允许将链表用作堆栈、队列或双端队列。
List 接口只是一个 List，即您可以添加或删除。因此，List 接口的基本实现必须只提供那些简单的方法，例如 ArrayList。 Deque接口是双端队列，iava的LinkedList IS-A双端队列。
As the JavaDocs states:
These operations allow linked lists to be used as a stack, queue, or double-ended queue.
The List interface is just a List i.e. you can add or remove. So a basic implementation of the List interface has to just provide those simple methods e.g. ArrayList. The Deque interface is the double ended Queue and iava's LinkedList IS-A Double Ended Queue.
IIRC，
deque代表双端队列。在您提到的情况下，将通用List定义为双端队列是不合逻辑的。例如，ArrayList不是为Deque接口设计的。插入在列表的末尾是有效的，但绝对不是在列表的开头（因为我认为这会导致整个数组的重新分配）。另一方面，
LinkedList是为Deque接口完美设计的，因为它是一个双链表。IIRC,
dequestands fordouble end queue. In the case you mention, it's not logical to define a genericListas a deque. For instance, anArrayListis not designed for theDequeinterface. Insertions will be efficient in the end of the list, but absolutely not at its beginning (because it will cause the re-allocation of a whole array, I think).The
LinkedListis, on the other end, perfectly designed for theDequeinterface, as it is a double linked list.由于双端队列可能使用
LinkedList以外的其他方式实现，并且代码可能依赖于任何具有此类功能的东西，因此Deque接口需要单独提供。List本身不应该实现/扩展Deque，因为在列表开头添加/删除可能不是每个实现都能（轻松）支持的。Because a double-ended queue might be implemented using something other than a
LinkedListand one's code may depend on anything with such functionality, so theDequeinterface needs to be available separately.Listshould not itself implement/extendDequebecause adding to/removing from the start of a list may not be something that can be (easily) supported by every implementation.