java 传值

public   class   Test  
{   public int   i,j;    
    public   void   test_m(Test   a)  
    {     Test   b   =  new   Test();  
          b.i   =   1;  
          b.j   =   2;  
          a   =   b;  
    }  
    public   void   test_m1(Test   a   )  
    {     a.i   =   1;  
        a.j   =   2;  
    }  
    public   static   void   main(String   argv[])  
    {     Test   t=   new   Test();  
          t.i   =   5;  
          t.j   =   6;  
          System.out.println( "t.i   =   "+   t.i   +   "   t.j=   "   +   t.j); //5,6  
          t.test_m(t);  
          System.out.println( "t.i   =   "+   t.i   +   "   t.j=   "   +   t.j); //5,6,a和t都指向了一个对象，而在test_m中s又指向了另一个对象，所以对象t不变！！！  
  
          t.test_m1(t);  
  
          System.out.println( "t.i   =   "+   t.i   +   "   t.j=   "   +   t.j); //1,2  
    }  
}