10.java

// Using run-time polymorphism.
class Figure {
    double dim1;
    double dim2; 

    Figure(double a, double b) {
        dim1 = a;
        dim2 = b;
    }

    double area() {
        System.out.println("Area for Figure is undefined.");
        return 0;
    }
}

class Rectangle extends Figure {
    Rectangle(double a, double b) {
        super(a, b);
    }

    // override area for rectangle
    double area() {
        System.out.println("Inside Area for Rectangle.");
        return dim1 * dim2;
    }
}

class Triangle extends Figure {
    Triangle(double a, double b) {
        super(a, b);
    }

    // override area for right triangle
    double area() {
        System.out.println("Inside Area for Triangle.");
        return dim1 * dim2 / 2;
    }
}

class FindAreas {
    public static void main(String args[]) {
        Figure f = new Figure(10, 10);
        Rectangle r = new Rectangle(9, 5);
        Triangle t = new Triangle(10, 8);
        
        Figure figref;

        figref = r;
        System.out.println("Area is " + figref.area());
        
        figref = t;
        System.out.println("Area is " + figref.area());
        
        figref = f;
        System.out.println("Area is " + figref.area());
    }
}