前面已经声明过了three是int类型，不能重复声明，直接写three=one+two，后面都不能再写int了

直接在输出后面写公式就好可，干嘛还要int，这样太复杂了。

public class HelloWorld{

    public static void main(String[] args) {

    int one = 10 ;

        int two = 20 ;

        int three = 30 ;

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

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

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

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

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

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

}

}