Abstraction Using abstract methods and classes

// Using abstract methods and classes. 
abstract class Figure { 
double dim1; 
double dim2; 
Figure(double a, double b) { 
dim1 = a; 
dim2 = b; 
} 
// area is now an abstract method 
abstract double area(); 
}

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 AbstractAreas { 
public static void main(String args[]) { 
// Figure f = new Figure(10, 10); // illegal now 
Rectangle r = new Rectangle(9, 5); 
Triangle t = new Triangle(10, 8); 
Figure figref; // this is OK, no object is created 
figref = r; 
System.out.println("Area is " + figref.area()); 
figref = t; 
System.out.println("Area is " + figref.area()); 
} 
}