JAVA多线程问题,求助,在线等

Question

import java.math.*;
import java.util.*;
class multi_track implements Runnable
{   
    static int NUM=0;
    static int temp=2;
    static int N=100;
    public boolean judge_prime(int N)
    { 
      if(N==2)return true;
      if(N%2==0) 
      return false;
       for(int i=3;i<=Math.sqrt(N);i+=2)
        {  
          if(N%i==0)
          return false;
        } 
      return true;
    }
public void run()
{       
         
   
             multi_track sin=new multi_track();
             for(;temp<N;temp++)
             if(sin.judge_prime(temp)==true)
             {
              System.out.println(temp);
                 NUM++;
               System.out.println(Thread.currentThread());
             }
           
       }
   public static void main(String[] args) 
  {  
      
      long startTime=System.nanoTime();
      Runnable Thread_1=new multi_track();
      Runnable Thread_2=new multi_track();
      Thread t1=new Thread(Thread_1);
      Thread t2=new Thread(Thread_2);
      t1.start();
      t2.start();
     while(t1.isAlive()||t2.isAlive());
      System.out.println(NUM);
      System.out.println(temp);
      long endTime=System.nanoTime();
       
       System.out.println(endTime-startTime);
   }
}