import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
import java.util.*;
public class Bounce {
public static void main(String[] args){
BounceFrame frame = new BounceFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
class Ball{
private static final int XSIZE = 15;
private static final int YSIZE = 15;
private double x = 0;
private double y = 0;
private double dx = 1;
private double dy = 1;
public void move(Rectangle2D bounds){
x = x + dx;
y = y + dy;
if(x<bounds.getMinX()){
x = bounds.getMinX();
dx = -dx;
}
if(x+XSIZE>=bounds.getMaxX()){
x = bounds.getMaxX()-XSIZE;
dx = -dx;
}
if(y<bounds.getMinY()){
y = bounds.getMinY();
dy = - dy;
}
if(y+YSIZE>=bounds.getMaxY()){
y = bounds.getMaxY()-YSIZE;
dy = -dy;
}
}
public Ellipse2D getShape(){
return new Ellipse2D.Double(x,y,XSIZE,YSIZE);
}
}
class BallPanel extends JPanel{
private ArrayList<Ball> balls = new ArrayList<Ball>();
public void add(Ball b){
balls.add(b);
}
public void paintCommponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D)g;
for(Ball b : balls){
g2.fill(b.getShape());
}
}
}
class BounceFrame extends JFrame{
private BallPanel panel;
private JPanel buttonPanel;
private JButton btnStart,btnClose;
private static final int DEFAULT_WIDTH = 450;
private static final int DEFAULT_HEIGHT = 350;
public static final int STEPS = 1000;
public static final int DELAY = 3;
public BounceFrame(){
setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);
setTitle("Bounce");
setLayout(new BorderLayout());
panel = new BallPanel();
add(panel,BorderLayout.CENTER);
buttonPanel = new JPanel();
btnStart = new JButton("Start");
btnClose = new JButton("Close");
add(buttonPanel,BorderLayout.SOUTH);
buttonPanel.add(btnStart);
buttonPanel.add(btnClose);
btnStart.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent enent){
addBall();
}
});
btnClose.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent enent) {
System.exit(0);
}
});
}
public void addBall(){
try{
Ball ball = new Ball();
panel.add(ball);
for(int i = 1;i<=STEPS;i++){
ball.move(panel.getBounds());
panel.paint(panel.getGraphics());
Thread.sleep(DELAY);
}
}catch(Exception er){
er.printStackTrace();
}
}
}
为什么我运行的时候我画的哪个圆显示不出来.
