[说明] 下面程序定义了一个类Shape及其成员函数，然后从类Shape派生出类Point、类Circle、类Cylinder，以及它们的成员函数。 [Java程序] (1) Shape public abstract void printShapeName(); //纯虚函数。 public double area()return 0.0; public double volumn()return 0.0; class Point extends Shape private double x.y; public Point (double a, double b)x=a; y=b; public void setPoint (double a,double b)x=a;y=b; final public double getX() return x; final public double getY()return y; public void printShapeName() (2) ; class Circle extends Point private double radius; public Circle(double r, double a, double b) (3) ; radius=r＞0 r:0; public void setRadius (double r) radius=r＞0 r:0; public double getRadius () return radius; public double area()return 3.14259 * radius * radius; public void printshapeName () System.out.print ("circle: ") ; ; ; class Cylinder (4) private double height; public Cylinder(double h, double r, double x, double y) super (r, x, y) ; height = h＞0 h:0; public void setHeight (double h) height = h＞0 h:0; public double area () //计算表面积 return (5) ; public double volumn () double r=super.getRadius () ; return 3.14159 * r * r * height; public void printShapeName () System. out .print ("cylinder: ") ;