5-13.txt

清华大学第二版

程序5-13
interface Shape2D{	//定义Shape2D接口
	final double pi=3.14;	//数据成员一定要初始化
	public abstract double area();	//抽象方法，不需要定义处理方式
}

class Circle implements Shape2D{
	double radius;
	public Circle(double r){	//构造方法
		radius=r;
	}
	public double area(){
		return (pi * radius * radius);
	}
}

class Rectangle implements Shape2D{
	int width,height;
	public Rectangle(int w,int h){	//构造方法
		width=w;
		height=h;
	}
	public double area(){
		return (width * height);
	}
}
public class InterfaceTester {
	public static void main(String args[]){
		Rectangle rect=new Rectangle(5,6);
		System.out.println("Area of rect = " + rect.area());
		Circle cir=new Circle(2.0);
		System.out.println("Area of cir = " + cir.area());
	}
}