Using Super

class Triangle{
    double base, height;
    Triangle(){
        base = 0;
        height = 0;
    }
    Triangle(Triangle tri){
        base = tri.base;
        height = tri.height;
    }
    Triangle(double base, double height){
        this.base = base;
        this.height = height;
    }
    Triangle(double len){
        this.base = len;
        this.height = len;
    }
    void area(){
        System.out.println(0.5*base*height);
    }
}
class Demo extends Triangle{
    double length;
    Demo(double h, double b, double l){
        super(h,b);
        length = l;
    }
    Demo(Demo dm){
        super(dm);
        length = dm.length;
    }
    void area(){
        System.out.println(height*base*length);
    }
}
public class Main{
    public static void main(String args[]){
        Triangle tri = new Triangle(5.0,3.0);
        Demo dm = new Demo(5.0,3.0,3.0);
        tri.area();
        dm.area();
    }
}