Vector and Hashtable are two collection classes that are inherently thread safe or synchronized; whereas, the classes ArrayList and HashMap are unsynchronized a... [hashmap]
HashMap是Hashtable的轻量级实现（非线程安全的实现），他们都完成了Map接口，主要区别在于HashMap允许空（null）键值（key）,由于非线程安全，效率上可能高于Hashtable。HashMap允许将null... [hashmap]