int one = 10;
        int two = 20;
        int three = 0;
        three = one + two;  20+10
        System.out.println("three = one + two ==>"+three);    three = 30;
        three += one;    30+10
        System.out.println("three = one + two ==>"+three);    three = 40;
        three -= one;    
        System.out.println("three = one - two ==>"+three);