(JAVA)ConcurrentHashMap initialCapacity 手动计算初始化容量大小过程

(JAVA)ConcurrentHashMap initialCapacity 手动计算初始化容量大小过程

package com.lius.test;import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;/*** (JAVA)ConcurrentHashMap initialCapacity 手动计算初始化容量大小过程* * 第一步：int cap = ((initialCapacity>=(MAXIMUM_CAPACITY/2))?MAXIMUM_CAPACITY:* 							initialCapacity+(initialCapacity/2) + 1);* initialCapacity如果大于最大值的一半,cap直接取最大值，否则取initialCapacity+initialCapacity/2再+1的值作为cap变量值* 第二部: cap = (cap-1)|/2|/4|/8|/16|/32;  解释:|/ => [cap/=2; cap|=cap;]* cap先自减1，然后除以2在进行或运算，...除以32再进行或运算，取最终结果* 第三步: cap = (cap<0)?1:(cap>=MAXIMUM_CAPACITY)?MAXIMUM_CAPACITY:cap+1;  * 如果cap小于0,cap取1，如果大于最大值，cap就取最大值，如果cap在0与最大值之间，cap就取cap+1* @author lius*/
public class testMap {private static final int MAXIMUM_CAPACITY = 0x40000000;//initialCapacity = 64private Map<String,Object> mapContainer = new ConcurrentHashMap<>(64);//mainProgram Point
public static void main(String[] args) {testMap tMap = new testMap();tMap.run();
}private void run() {//initialCapacity = 64int initialCapacity = 64;//MAXIMUM_CAPACITY >>> 1  equals MAXIMUM_CAPACITY/=2;//initialCapacity >>> 1   equals initialCapacity/=2;/*** int cap = ((initialCapacity  >= (MAXIMUM_CAPACITY/2)) ?MAXIMUM_CAPACITY :initialCapacity + (initialCapacity/2) + 1);*///int cap = 64+(64/2+1);    97int cap = ((initialCapacity  >= (MAXIMUM_CAPACITY >>> 1)) ?MAXIMUM_CAPACITY :initialCapacity + (initialCapacity >>> 1) + 1);//cap = (cap-1)|/2|/4|/8|/16|/32; cap = tableSizeFor(cap);
}
//
private static final int tableSizeFor(int c) {/*** n = (n-1)|/2|/4|/8|/16|/32; */int n = c - 1;//	n = c-1;n |= n >>> 1; //	n/=2;  96|48  0b1100000|0b0110000 => 0b1110000  112n |= n >>> 2; //	n/=4;  112|28 0b1110000|0b0011100 => 0b1111100  124n |= n >>> 4; //	n/=8;  124|31 0b1111100|0b0011111 => 0b1111111	127n |= n >>> 8; //    n/=16; 127|7  0b1111111|0b0000111 => 0b1111111  127n |= n >>> 16;//    n/=32; 127|3  0b1111111|0b0000011 => 0b1111111  127//n == 127; 127<0?1:(n>=max?max:127+1) => 128return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;//return 128;
}
}