清华大学：JAVA教学课件：8-17

程序8-17：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class DrawingExample implements ActionListener {
JFrame frame;
MyButton button;
MyPanel panel;
int tag = 1;
public static void main(String args[]) {
DrawingExample de = new DrawingExample();
de.go();
}
public void go() {
frame = new JFrame("Drawing Example");
button = new MyButton("Draw");
button.addActionListener(this);
frame.getContentPane().add(button,"South");
panel = new MyPanel();
frame.getContentPane().add(panel,"Center");

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(360,200);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent e) {
//按钮上的文本在Draw与Clear间切换
if (tag==0) {
tag = 1;
button.setText("Draw");
}else {
tag = 0;
button.setText("Clear");
}
panel.repaint();//重绘panel
}
//自定义的button
class MyButton extends JButton {
MyButton(String text) {
super(text);
}
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.red);
int width = getWidth();
int height = getHeight();
g.drawOval(4,4,width-8,height-8);//绘制椭圆
}
}
//自定义的panel
class MyPanel extends JPanel {
protected void paintComponent(Graphics g){
super.paintComponent(g);
if (tag==0) {
g.setColor(Color.blue); //设置颜色
g.drawLine(40,25,30,50); //绘制直线
g.setColor(Color.green);
g.drawRect(100,50,100,46);//绘制矩形
g.setColor(Color.red);
g.drawRoundRect(73,32,56,37,10,16); //绘制圆角矩形
g.setColor(Color.yellow);
g.fillOval(180,60,60,45); //绘制填充椭圆
g.setColor(Color.pink);
g.fillArc(250,32,90,60,15,30); //绘制填充圆弧
}
}
}
}