// The Shape class is an abstract class that serves as the superclass of a
// family of Shape classes.  It implements the Comparable interface, ordering
// shapes by their area.
public abstract class Shape implements Comparable<Shape> {
    private String name;
    
    public Shape(String name) {
        this.name = name;
    }
    
    public abstract double area();
    
    public final int compareTo(Shape other) {
        double difference = area() - other.area();
        if (difference < 0) {
            return -1;
        } else if (difference > 0) {
            return 1;
        } else { // difference == 0
            return 0;
        }
    }
    
    public final String toString() {
        return name + " of area " + area();
    }
}