Vector
Hashtable
ConcurrentHashMap
StringBuffer
Enumeration(枚举,相当于迭代器)
ConcurrentHashMap与Hashtable的区别:https://www.cnblogs.com/DDiamondd/p/10722160.html
HashMap与Hashtable的区别:https://www.cnblogs.com/DDiamondd/p/10721539.html