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要求

定义4个类，MyShape、MyLine、MyRectangle和MyOval，其中MyShape是其他三个类的父类。MyShape为抽象类，包括图形位置的四个坐标；一个无参的构造方法，将所有的坐标设置为0；一个带参的构造函数，将所有的坐标设置为相应值；每个坐标的设置和读取方法；abstract void draw(Graphics g)方法。MyLine类负责画直线，实现父类的draw方法；MyRectangle负责画矩形，实现父类的draw方法；MyOval负责画椭圆，实现父类的draw方法。编写一个应用程序，使用上面定义的类，随机选取位置和形状，绘制20个图形。示例输出如图所示。

代码

import javax.swing.*;
import java.util.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;abstract class MyShape{int x = 0;int y = 0;int z = 0;int k = 0;public MyShape(){;}public abstract void draw(Graphics g);
}class MyLine extends MyShape{Random rd = new Random();@Overridepublic void draw(Graphics g){g.drawLine(x,y,z,k);}public MyLine(){int _x = rd.nextInt(200);int _y = rd.nextInt(200);int _z = rd.nextInt(200);int _k = rd.nextInt(200);x = _x;y = _y;z = _z;k = _k;}
}class MyRectangle extends MyShape{Random rd = new Random();@Overridepublic void draw(Graphics g){g.drawRect(x,y,z,k);}public MyRectangle(){int _x = rd.nextInt(200);int _y = rd.nextInt(200);int _z = rd.nextInt(200);int _k = rd.nextInt(200);x = _x;y = _y;z = _z;k = _k;}
}class MyOval extends MyShape{Random rd = new Random();@Overridepublic void draw(Graphics g){g.drawOval(x,y,z,k);}public MyOval(){int _x = rd.nextInt(200);int _y = rd.nextInt(200);int _z = rd.nextInt(200);int _k = rd.nextInt(200);x = _x;y = _y;z = _z;k = _k;}
}class DrawComponent extends JComponent
{@Overridepublic void paintComponent(Graphics g){for(int i=0;i<20;i++) {if(i<6) {MyOval mo = new MyOval();mo.draw(g);}else if(i<12) {MyRectangle mr = new MyRectangle();mr.draw(g);}else {MyLine ml = new MyLine();ml.draw(g);}}}
}class Game extends JFrame{Random rd = new Random();public Game(){this.add(new DrawComponent());this.setSize(600,600);this.setTitle("Graphics");this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);this.setLocationRelativeTo(null);this.setVisible(true);}
}public class Main1{public static void main(String [] args){new Game();}
}

代码分析

• 使用抽象类
• 覆写draw方法来绘画
• 自定一个JComponent来调用各类的绘画方法