shapeccd_ex.java

刘艺编著的java教程的课本习题加例题代码 很有用哦！

abstract class Shape    
{abstract protected double area();
 }
class Circle extends Shape
{float r;
 public Circle(float a)
  {r=a;}
 public double area()
 {System.out.print("Calculate the area of circle:  ");
   return Math.PI*r*r;}
 }
class Cylinder extends Circle
{float h;
 public Cylinder(float a,float b)
  {super(a);
   h=b;}
 public double area()
 {System.out.print("Calculate the area of cylinder:  "); 
  return 2*Math.PI*r*r+2*Math.PI*r*h;}
 }
public class Shapeccd_ex
{public static void main(String args[])
 {Circle cl=new Circle(3);
  Cylinder cd=new Cylinder(2,5);
  System.out.println(cl.area());
  System.out.println(cd.area());
  cl=cd;
  System.out.println(cl.area());}
}