Circle和Triangle是Geometry的子类
public class Geometry{ public double area(){ return 0; } }
public class Circle extends Geometry{ private double r; public Circle(double r){ this.r=r; }
public double area(){ double t; t=Math.PI*r*r; return t; } }
public class Triangle extends Geometry{ private double a; private double b; private double c; public Triangle(double a,double b,double c){ this.a=a; this.b=b; this.c=c;
} public double area(){ double p; double t; p=(a+b+c)/2; t=Math.sqrt(p*(p-a)*(p-b)*(p-c)); return t; } }
public class Example01{ public static void main(String args[]){ Geometry g; g=new Circle(2); System.out.println(g.area()); } }
