import java.util.Collections;

 import java.util.HashMap;

 import java.util.HashSet;

 import java.util.Hashtable;

 import java.util.Map;

 import java.util.concurrent.ConcurrentHashMap;

 //测试三种并发集合的读写效率

 public class ConcurrentHashMapTest {

     public static void main(String[] args) {

         //HashMap不是线程安全的,通过 Collections.synchronizedMap()转换成线程安全的.

         final Map<Integer, Integer> hm = Collections.synchronizedMap(new HashMap<Integer, Integer>());

         //HashTable内部自带同步,线程安全的.

         final Map<Integer, Integer> ht = new Hashtable<Integer, Integer>();

         //JDK1.5之后提供的并发集合.

         final Map<Integer, Integer> chm = new ConcurrentHashMap<Integer, Integer>();

         putMap(hm);//输出:13321

         putMap(ht);//输出:11834

         putMap(chm);//输出:8312  数据量达到一定程度之后,会比前两种快3~4倍左右.

     }

     private static void putMap(final Map<Integer, Integer> hm) {

         long begin = System.currentTimeMillis();

         for (int k = 0; k < 100; k++) {//为了让效果更明显,再循环100次.

             for (int i = 0; i < 1000; i++) {//1000条线程

                 final int key = i;

                 new Thread(new Runnable() {

                     @Override

                     public void run() {

                         for (int j = 0; j < 1000; j++) {//每条线程向其中添加1000次

                             hm.put(key, j);

                         }

                     }

                 }).start();

             }

         }

         long end = System.currentTimeMillis();

         System.out.println(end - begin);

     }

 }