debugsquare.java

北京大学出版社的

package questions.c5;
class DebugShape {
   public abstract double getPerimeter() {};
   public abstract double getArea() {};
}
public class DebugSquare extends DebugShape {
   private double length;
   public DebugSquare( double l ) {
      length = l;
   }
   public abstract double getPerimeter() {
      return 4 * length;
   }
   public abstract double getArea() {
      return length * length;
   }
}