public class HelloWorld{

    public static void main(String[] args) {

    int one = 10 ;

        int two = 20 ;

        int three = 0 ;这个地方已经有定义了three变量

        three=one+two;所以在这里加int会出现报错

//

error: variable three is already defined in method main(String[])
        int three=one+two;

//

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

        three=three+one;

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

        three=three-one;

        System.out.println(" three -= one ==> "+three);

        three=three*one;

        System.out.println(" three *= one ==> "+three);

        three=three/one;

        System.out.println(" three /= one ==> "+three);

        three=three%one;

        System.out.println(" three %= one ==> "+three);

}

}