three -= one; （此处three=40，上一步得到的）  //three-=one ==40-10=30

        System.out.println(three);  //30

        three *= one;    //300

        System.out.println(three);

        three /= one;  //30

        System.out.println(three);

        three %= one;

        System.out.println(three);  0

 int one = 10 ;

        int two = 20 ;

        int three = 0 ;

        three = one+two; = 30

        three += one;  =40

        System.out.println(three);  

        three -= one; （此处three=40，上一步得到的）

        System.out.println(three);

        three *= one;

        System.out.println(three);

        three /= one;

        System.out.println(three);

        three %= one;

        System.out.println(three);

 别忘了，three的值一直在变化