This class implements the Set interface, backed by a hash table (actually a HashMapinstance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.
HashSet是基于HashMap来实现的,操作很简单,更像是对HashMap做了一次“封装”,而且只使用了HashMap的key来实现各种特性,我们先来感性的认识一下这个结构:
其大致的结构是这样的:
map
是整个HashSet的核心,而PRESENT
则是用来造一个假的value来用的。
基本操作也非常简单,就是调用HashMap的相关方法,其中value就是之前那个dummy的Object。所以,只要了解#7 HashMap的实现就可以了。