Using super class Constructor

class Triangle{
    double base, height;
    Triangle(){
        base = 0;
        height = 0;
    }
    Triangle(double base, double height){
        this.height = height;
        this.base = base;
    }
    Triangle(double len){
        height = len;
        base = len;
    }
    void area(){
        System.out.println("The area of a Triangle is: " + 0.5*base*height);
    }
}
class Demo extends Triangle{
    double length;
    Demo(double b, double h, double l){
        base = b;
        height = h;
        length = l;
    }
    void area(){
        System.out.println(base*height*length);
    }
}
public class Main{
    public static void main(String args[]){
        Triangle tri = new Triangle(5.0,3.0);
        Demo dm  = new Demo(3.0,7.0,5.0);
        tri.area();
        dm.area();
    }
}