// Class to represent a square
public class Square implements Shape {
   private double side;
   
   public Square(double side) {
      this.side = side;
   }
   
   // returns the area of this square
   public double area() {
      return side * side;
   }
   
   // compares this square to other by area
   // pre: other != null
   public int compareTo(Shape other) {
      if (this.area() < other.area()) {
         return -1;
      } else if (this.area() > other.area()) {
         return 1;
      } else {
         return 0;
      }
   }
   
   public String toString() {
      return "square of area " + String.format("%.3f", area());
   }   
}