几何的类

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());
 }
}