书读的少你别骗我。。。hashmap源码  int capacity = 1 ; // 初始容量

14 while (capacity < initialCapacity) //确保容量为2的n次幂，使capacity为大于initialCapacity的最小的2的n次幂 15 capacity <<= 1; 16 17 this.loadFactor = loadFactor; 18 threshold = (int)(capacity * loadFactor); 19 table = new Entry[capacity]; 

1. if  (numKeysToBeAdded > threshold) {  
2.             // 重新计算新的容量先resize   
3.             int  targetCapacity = ( int )(numKeysToBeAdded / loadFactor +  1 );  
4.             if  (targetCapacity > MAXIMUM_CAPACITY)  
5.                 targetCapacity = MAXIMUM_CAPACITY;  
6.             int  newCapacity = table.length;  
7.             while  (newCapacity < targetCapacity)  
8.                 newCapacity <<= 1 ;  
9.             if  (newCapacity > table.length)  
10.                 resize(newCapacity);