==>是什么有什么用？

不加不也能正常运行吗？

  int one = 10 ;

       int two = 20 ;

       int three = 0 ;

       three = one + two ;

       System.out.println(three = one + two);

       System.out.println(  three += one  );

       System.out.println(three -= one);

       System.out.println( three *= one);

       System.out.println( three /= one);

       System.out.println( three %= one);