HashMap 与 ConcurrentHashMap 在初始化不同大小容量时，实际分配的空间情况

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HashMap.java 

int capacity = 1;
    
int initialCapacitys[] = {1,2,3,4,5,6,7,8,9,10,11,13,15,16,17,26,31,32,33,50,60,63,64,65};
    
for(int initialCapacity : initialCapacitys)
{
    while (capacity < initialCapacity)
        capacity <<= 1;
        
    System.out.println("initialCapacity:" + initialCapacity + ", capacity:" + capacity);
}
    
/*
this.loadFactor = loadFactor;
threshold = (int)Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
table = new Entry[capacity];
 */

输出结果：

initialCapacity:1, capacity:1
initialCapacity:2, capacity:2
initialCapacity:3, capacity:4
initialCapacity:4, capacity:4
initialCapacity:5, capacity:8
initialCapacity:6, capacity:8
initialCapacity:7, capacity:8
initialCapacity:8, capacity:8
initialCapacity:9, capacity:16
initialCapacity:10, capacity:16
initialCapacity:11, capacity:16
initialCapacity:13, capacity:16
initialCapacity:15, capacity:16
initialCapacity:16, capacity:16
initialCapacity:17, capacity:32
initialCapacity:26, capacity:32
initialCapacity:31, capacity:32
initialCapacity:32, capacity:32
initialCapacity:33, capacity:64
initialCapacity:50, capacity:64
initialCapacity:60, capacity:64
initialCapacity:63, capacity:64
initialCapacity:64, capacity:64
initialCapacity:65, capacity:128

ConcurrentHashMap.java

int concurrencyLevel = 16; //默认是16
int MIN_SEGMENT_TABLE_CAPACITY = 2;
      
int sshift = 0;
int ssize = 1;
while (ssize < concurrencyLevel) {
    ++sshift;
    ssize <<= 1;
}        
      
int initialCapacitys[] = {1,10,16,31,32,33,63,64,65,127,128,129,256,257,512,513,1024,1025,2048,4096,8192,16384};
      
for(int initialCapacity : initialCapacitys)
{
    int c = initialCapacity / ssize;
    if (c * ssize < initialCapacity)
        ++c;
          
    int cap = MIN_SEGMENT_TABLE_CAPACITY;
          
    while (cap < c)
        cap <<= 1;
          
    System.out.println("initialCapacity:" + initialCapacity + ", c:" + c + ", cap:" + cap + ", ssize:" + ssize);
}
      
// create segments and segments[0]
/*
Segment<K,V> s0 =
    new Segment<K,V>(loadFactor, (int)(cap * loadFactor),
                     (HashEntry<K,V>[])new HashEntry[cap]);
Segment<K,V>[] ss = (Segment<K,V>[])new Segment[ssize];
*/

输出结果：

initialCapacity:1, c:1, cap:2, ssize:16
initialCapacity:10, c:1, cap:2, ssize:16
initialCapacity:16, c:1, cap:2, ssize:16
initialCapacity:31, c:2, cap:2, ssize:16
initialCapacity:32, c:2, cap:2, ssize:16
initialCapacity:33, c:3, cap:4, ssize:16
initialCapacity:63, c:4, cap:4, ssize:16
initialCapacity:64, c:4, cap:4, ssize:16
initialCapacity:65, c:5, cap:8, ssize:16
initialCapacity:127, c:8, cap:8, ssize:16
initialCapacity:128, c:8, cap:8, ssize:16
initialCapacity:129, c:9, cap:16, ssize:16
initialCapacity:256, c:16, cap:16, ssize:16
initialCapacity:257, c:17, cap:32, ssize:16
initialCapacity:512, c:32, cap:32, ssize:16
initialCapacity:513, c:33, cap:64, ssize:16
initialCapacity:1024, c:64, cap:64, ssize:16
initialCapacity:1025, c:65, cap:128, ssize:16
initialCapacity:2048, c:128, cap:128, ssize:16
initialCapacity:4096, c:256, cap:256, ssize:16
initialCapacity:8192, c:512, cap:512, ssize:16
initialCapacity:16384, c:1024, cap:1024, ssize:16

2013-05-14

HashMap 与 ConcurrentHashMap 在初始化不同大小容量时，实际分配的空间情况

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原文地址：http://www.cnblogs.com/personnel/p/4584896.html