//   interface--------abstract class-----------class
//     abstract---------------------------concrete

// Simple interface for a shape
public abstract class Shape implements Comparable<Shape> {
   private String name;
   
   public Shape(String name) {
      this.name = name;
   }

   public abstract double area();
   
   // compares this rectangle to other by area
   // pre: other != null
   public final int compareTo(Shape other) {
      if (this.area() < other.area()) {
         return -1;
      } else if (this.area() > other.area()) {
         return 1;
      } else {
         return 0;
      }
   }
   
   public final String toString() {
      return name + " of area " + String.format("%.3f", area());
   }
   
}