demoofsimplefigure.java

提供了常用的JAVA技术的示例

/*
 例5-23  用接口改造 例5-22   增加 area()
 增加了四个返回值，将其显示出来。

 问题：  如果不用接口定义 Area(),程序也可以实现！
        坐标量有什么作用??  去掉也可以吗？
*/
package DemoOfSimpleFigure;

import javax.swing.UIManager;
import java.awt.*;

interface Shape{
    int position_x=50,position_y=50;  // 坐标量有什么作用??
    double PI=3.1415926;
    //void draw();
}

interface Area extends Shape{
    //double area();
}

class Square implements Shape,Area{
    private int length;
    void setSize(int l){
        length=l;
    }
    int give(){
        return length;
    }
    public void draw(){
        System.out.print("this is a square.");
    }
    public double area(){
        return length*length;
    }
}


class Circle implements Shape,Area{
    private int radius;
    void setSize(int r){
        radius=r;
    }
    int give(){
        return radius;
    }
    public void draw(){
        System.out.print("this is a circle.");
    }
    public double area(){
        return PI*radius*radius;
    }
}


class Trigon implements Shape,Area{
    private int bottom;
    private int highness;
    void setSize(int b,int h){
        bottom=b;
        highness=h;
    }
    int give1(){
        return bottom;
    }
    int give2(){
        return highness;
    }
    public void draw(){
        System.out.print("this is a Trigon.");
    }
    public double area(){
        return 0.5*bottom*highness;
    }
}

public class DemoOfSimpleFigure {
    public static void main(String[] args) {
        Square sq=new Square();
        Circle ci=new Circle();
        Trigon tr=new Trigon();

        sq.draw();
        sq.setSize(5);
        System.out.print("  length="+sq.give()+"  Area="+sq.area()+"\n");

        ci.draw();
        ci.setSize(2);
        System.out.print("  radius="+ci.give()+"  Area="+ci.area()+"\n");

        tr.draw();
        tr.setSize(4,3);
        System.out.print("  bottom="+tr.give1()+"  highness="+tr.give2()+"  Area="+tr.area());
  }
}