（初学者）为什么按自己最笨的方法能运行但是答案是错的啊~

public class HelloWorld{

    public static void main(String[] args) {

    int one = 10 ;

        int two = 20 ;

        int three = 0 ;

        int s1 = one+two;

        System.out.println("three = one +two==>"+s1);

        int s2 =three+one;

        System.out.println("three += one ==>"+s2);

        int s3 =three-one;

        System.out.println("three -= one ==>"+s3);

        int s4 =three*one; 

        System.out.println("three *= one ==>"+s4);

        int s5 = three/one;                 

        System.out.println("three /= one ==>"+s5);

        int s6 = three%one;

        System.out.println("three %= one ==>"+s6);

}

}