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java的vector类为什么被认为过时了 #43

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## 为什么Java的```Vector```类被认为是过时的或者废弃的
### 问题
为什么java ```Vector```类被认为是一个遗留的,过时的或废弃的类?在并发操作时,使用它是无效的吗?

如果我不想手动对对象实现同步,只想用一个线程安全的集合而无需创建底层数组的全新副本(如```CopyOnWriteArrayList```一样)。这种情况下,我使用```Vector```合理吗?

然后就是关于栈的问题,它是Vector的一个子类,我应该用什么代替它?
### 回答
Vector中对每一个独立操作都实现了同步,这通常不是我们想要的做法。对单一操作实现同步通常不是线程安全的(举个例子,比如你想遍历一个Vector实例。你仍然需要申明一个锁来防止其他线程在同一时刻修改这个Vector实例。如果不添加锁的话

通常会在遍历实例的这个线程中导致一个``` ConcurrentModificationException ```)同时这个操作也是十分慢的(在创建了一个锁就已经足够的前提下,为什么还需要重复的创建锁)

当然,即使你不需要同步,Vector也是有锁的资源开销的。

总的来说,在大多数情况下,这种同步方法是存在很大缺陷的。正如Mr Brain Henk指出,你可以通过调用```Collections.synchronizedList```来装饰一个集合 -事实上 ```Vector``` 将"可变数组"的集合实现与"同步每一个方法"结合起来的做法是另一个糟糕的设计;

各个装饰方法能够更明确的指示其关注的功能实现。

对于```Stack```这个类-我更乐于使用```Deque/ArrayDeque```来实现

stackoverflow讨论地址: http://stackoverflow.com/questions/1386275/why-is-java-vector-class-considered-obsolete-or-deprecated

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