Stack in Java

##前言 堆栈作为最基础的数据结构之一，在Java的最初版本就有了纯粹的标准实现：java.util.Stack。只可惜该实现存在性能缺陷，主要是由于主要的操作都加上了synchronized线程安全保护机制，导致无法被应用于对性能要求颇高的生产环境。

A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. For example: Deque stack = new ArrayDeque();

在Java Collections类发布后就和java.util.Vector类被一起被废弃了，取代之的是java.util.Deque接口。之所以设计成接口，是不想与某一个Deque的实现绑定。Java提供了LinkedList和ArrayDeque即可按照使用场景不同，采纳基于数组或是链表的Deque实现，提供了灵活性。

Deques can also be used as LIFO (Last-In-First-Out) stacks. This interface should be used in preference to the legacy Stack class. When a deque is used as a stack, elements are pushed and popped from the beginning of the deque.