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 >= initialCapacity11         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.