HashMap简单的实现ThreadLocal

/**
 * 用HashMap简单的实现ThreadLocal
 */
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import org.junit.Test;
public class MyThreadLocal {
 /**
  * 用一个弱引用保存value，便于线程结束后垃圾回收器的回收
  */
   private static Map<Thread,WeakReference<Integer>> map=new HashMap<Thread,WeakReference<Integer>>();
   public static Integer getNum(){
    //第一次先得WeakReference
    WeakReference<Integer> refer=map.get(Thread.currentThread());
    if(refer==null){
    //若为空，得到一个随机数，用这个随机数创建一个WeakReference对象，作为value存入map
     Random random=new Random();
     int number = random.nextInt(100);
     refer=new WeakReference<Integer>(number);
     map.put(Thread.currentThread(),refer );
    }
    //返回weakReference里保存的number
    return refer.get();
   }
   /**
    *以下是测试代码
    */
   public static void main(String[] args) {
    Integer num1 = MyThreadLocal.getNum();
    Integer num2 = MyThreadLocal.getNum();
    System.out.println(num1+":::"+num2);
    new Thread(){
     @Override
  public void run() {
   Integer num3 = MyThreadLocal.getNum();
   Integer num4 = MyThreadLocal.getNum();
   System.out.println(num3+":::"+num4);
  }
    }.start();
 }
}