java 接口实现多态

package unit4;
import java.awt.Graphics;

public interface Shape {
    void drowme(Graphics g);
    double area();
    double length();
    String getName();

}

package unit4;

import java.awt.Graphics;

public class Point implements Shape{
    int x,y;
    Point (int x,int y){this.x=x;this.y=y;}
    
    public double area() {
        // TODO Auto-generated method stub
        return 0;
    }
    public void drowme(Graphics g) {
        g.fillOval(x,y,5,5);
        
    }
    public String getName() {
        // TODO Auto-generated method stub
        return "Point";
    }
    public double length() {
        // TODO Auto-generated method stub
        return 0;
    }
}

package unit4;

import java.awt.Graphics;

public class Triangle implements Shape {
    Point a,b,c;
    public Triangle(Point aa,Point bb,Point cc) {
        // TODO Auto-generated constructor stub
        a=aa;
        b=bb;
        c=cc;
        
    }

    public double area() {
        
        double a_b=Math.sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
        double a_c=Math.sqrt((a.x-c.x)*(a.x-c.x)+(a.y-c.y)*(a.y-c.y));
        double b_c=Math.sqrt((b.x-c.x)*(b.x-c.x)+(b.y-c.y)*(b.y-c.y));
        double l=(a_b+a_c+b_c)/2;
        double s=Math.sqrt((l-a_b)*(l-b_c)*(l-a_c)*l);
        return s;
    }

    public void drowme(Graphics g) {
        g.drawLine(a.x,a.y,b.x,b.y);
        g.drawLine(a.x,a.y,c.x,c.y);
        g.drawLine(b.x,b.y,c.x,c.y);
        
    }

    public String getName() {
        return "triangle";
    }

    public double length() {
        double a_b=Math.sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
        double a_c=Math.sqrt((a.x-c.x)*(a.x-c.x)+(a.y-c.y)*(a.y-c.y));
        double b_c=Math.sqrt((b.x-c.x)*(b.x-c.x)+(b.y-c.y)*(b.y-c.y));
        double l=(a_b+a_c+b_c);
        return l;
    }
    

}

package unit4;

import java.awt.Graphics;

public class Circl implements Shape {

    Point c;
    int r;
    public Circl(Point cc,int rr) {
        c=cc;
        r=rr;
    }
    public double area() {
        return 3.14159*r*r;
    }

    public void drowme(Graphics g) {
        g.drawOval(c.x-r,c.y-r,2*r,2*r);
        
    }

    public String getName() {
        return "circle";
    }

    public double length() {
        return 2*3.14159*r;
    }
    

}

package unit4;

import java.awt.Graphics;

public class Rect implements Shape{
    Point a,b;
    Rect(Point aa,Point bb){a=aa;b=bb;}

    public double area() {
        
        return (a.x-b.x)*(a.y-b.y);
    }

    public void drowme(Graphics g) {
        g.drawRect(a.x,a.y,b.x-a.x,b.y-a.y);
        
    }

    public String getName() {
        return "rectangle";
    }

    public double length() {
        return (b.x-a.x)*2+(b.y-a.y)*2;
    }
    

}

package unit4;

import java.applet.Applet;
import java.awt.Graphics;

public class Shapetest extends Applet{
     Shape[]myshapes=new Shape[5];
    public  void init() {
        
         Point a0=new Point(50,50);
         Point a1 = new Point(24,24);
         Point a2=new Point(100,200);
         Point a3 = new Point(200,120);
         myshapes[0]=a0;
         myshapes[1]=new Triangle(a1,a2,a3);
         myshapes[2]=new Circl(a2,50);
         myshapes[3]=new Circl(a3,100);
         myshapes[4]=new Rect(new Point(100,100),new Point(200,200));
        
        
    }
    public void paint(Graphics g){
        for(int i=0;i<myshapes.length;i++){
            myshapes[i].drowme(g);
            System.out.println(myshapes[i].getName()+": area: "+myshapes[i].area()+", length: "+myshapes[i].length());
        }
    }

}

这里可以直接在eclipse上运行位applet，但是，我发现一个严重的问题，我没法部署网站，哎，先不管了，以后用到了在慢慢调吧。

每次都要费老大劲配置。我日。。

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <applet code="shapetest.class" width=400 height=400>
    </applet>

</body>
</html>

理论上，配置成功可以在网页上启动小程序的。