HashSet随笔

HashSet说白了其实就是HashMap.Entry[capacity], HashMap.Entry实现的链表 相当于LinkedList.

参数loadFactor对其性能有很大影响.

capacity: the number of buckets.

initialCapacity: Default value is 16, 用于初始化数组的槽位, capacity永远 >= initialCapacity 并且capacity永远为2的n次幂 最大值为1<<30.

因为源码已经解释的很清楚了.

 1 if (initialCapacity < 0)
 2             throw new IllegalArgumentException("Illegal initial capacity: " +
 3                                                initialCapacity);
 4         if (initialCapacity > MAXIMUM_CAPACITY)
 5             initialCapacity = MAXIMUM_CAPACITY;
 6         if (loadFactor <= 0 || Float.isNaN(loadFactor))
 7             throw new IllegalArgumentException("Illegal load factor: " +
 8                                                loadFactor);
 9 
10         // Find a power of 2 >= initialCapacity
11         int capacity = 1;
12         while (capacity < initialCapacity)
13             capacity <<= 1;
14 
15         this.loadFactor = loadFactor;
16         threshold = (int)(capacity * loadFactor);
17         table = new Entry[capacity];

loadFactor: Default value is 0.75, 影响resize容器的频率与内存占用, 越小则需要更多内存占用, 越大则增加get()与put()/putAll()的系统开销.

threshold: 始终为当前capacity*loadFactor, 每次添加数据时会判断size()是否 >= threshold, 大于则resize(). resize()的同时会再次计算新的threshold值.

 

posted @ 2012-12-18 17:57  D.Wang  阅读(177)  评论(0)  编辑  收藏  举报