class round{
    double x,y,r;
    round(double x,double y,double r){
        this.x=x;
        this.y=y;
        this.r=r;
    }
    double zc(){
        return (2*3.14159*r);
    }
    double mj(){
        return (3.14159*r*r);
    }
}

class column extends round{
    double h;
    column(int x,int y,int r,int h){
        this.x=x;
        this.y=y;
        this.r=r;
        this.h=h;
    }
    double mj(){
        return (2*3.14159*r*h);
    }
    double tj(){
        return (3.14159*r*r*h);
    }
}
为什么在column构造函数处提示Implicit super constructor round() is undefined. Must explicitly invoke another constructor