下面这个java多线程的笔试题怎么做？

Question

我觉得这个题应该考到volatile变量，虽然不大常用，借用了 tangweiwei_csdn() 的架子，不好意思，以下在Jbuilder9下通过：
public class Dif {
  volatile int hehe=0;
  Thread t1=new ThreadAdd1();
  Thread t2 = new ThreadAdd2();
  Thread t3 = new ThreadSub3();
  Thread t4 = new ThreadSub4();  class ThreadAdd1 extends Thread
{
        ThreadAdd1()
        {
                //this.start();;
        }
        public void run()
        {
                for(int i=0;i<10;i++)
                {
                hehe++;
                System.out.println("t1 Thread Run,Var="+hehe);
                try
                {
                sleep((int)Math.random()*1000);
                }catch(Exception E){}
                }
        }
}
class ThreadAdd2 extends Thread
{
        ThreadAdd2()
        {
                //this.start();;
        }
        public void run()
        {
                for(int i=0;i<10;i++)
                {
                hehe++;
                System.out.println("t2 Thread Run,Var="+hehe);
                try
                {
                sleep((int)Math.random()*1000);
                }catch(Exception E){}
                }
        }
}
class ThreadSub3 extends Thread
{
        ThreadSub3()
        {
                //this.start();;
        }
        public void run()
        {
                for(int i=0;i<10;i++)
                {
                hehe--;
                System.out.println("t3 Thread Run,Var="+hehe);
                try
                {
                sleep((int)Math.random()*1000);
                }catch(Exception E){}
                }
        }
}
class ThreadSub4 extends Thread
{
        ThreadSub4()
        {
                //this.start();;
        }
        public void run()
        {
                for(int i=0;i<10;i++)
                {
                hehe--;
                System.out.println("t4 Thread Run,Var="+hehe);
                try
                {
                sleep((int)Math.random()*1000);
                }catch(Exception E){}
                }
        }
}
  public Dif() {
    t1.start();
    t2.start();
    t3.start();
    t4.start();
  }  public static void main(String arg[])        {
    Dif dif=new Dif();
        }
}输出结果：（一种）
t1 Thread Run,Var=1t2 Thread Run,Var=2t3 Thread Run,Var=1t1 Thread Run,Var=2t2 Thread Run,Var=3t3 Thread Run,Var=2t4 Thread Run,Var=1t1 Thread Run,Var=2

t1 Thread Run,Var=2t2 Thread Run,Var=3t3 Thread Run,Var=2t4 Thread Run,Var=1t4 Thread Run,Var=0