类的封装与抽象

//Programme Name TestCylinder.java

class Circle

{

   private double radius;

    Circle()

{

radius=0.0;

}

Circle(double r)

{

radius=r;

}

double getPerimeter()

{

return 2*Math.PI*radius;

}

double getArea()

{

return Math.PI*radius*radius;

}

void disp()

{

System.out.println("圆半径 ="+radius);

System.out.println("圆周长 ="+getPerimeter());

System.out.println("圆面积 ="+getArea());

}

}

class Cylinder extends Circle

{

private double hight;

Cylinder(double r,double h)

{

super(r);

hight=h;

}

public double getVol()

{

return getArea()*hight;

}

public void dispVol()

{

System.out.println("圆柱体积 ="+getVol());

}

}

public class TestCylinder

{

public static void main(String[] args)

{

Circle Ci=new Circle(10.0);

Ci.disp();

Cylinder Cyl=new Cylinder(5.0,10.0);

Cyl.disp();

Cyl.dispV ol();

}

}