今天模拟书上的一个例题做了一个弹弹球，是在画布上的指定位置画多个圆，经过一段的延时后，在附近位置重新画。使球看起来是动，通过JSpinner组件调节延时，来控制弹弹球的移动速度.
BallsCanvas.java
public class BallsCanvas extends Canvas implements ActionListener,
FocusListener {
private Ball balls[]; // 多个球
private Timer timer;
private static class Ball {
int x, y; // 坐标
Color color; // 颜色
boolean up, left; // 运动方向
Ball(int x, int y, Color color) {
this.x = x;
this.y = y;
this.color = color;
up = left = false;
}
}
public BallsCanvas(Color colors[], int delay) { // 初始化颜色、延时
this.balls = new Ball[colors.length];
for (int i = 0, x = 40; i < colors.length; i++, x += 40) {
balls[i] = new Ball(x, x, colors[i]);
}
this.addFocusListener(this);
timer = new Timer(delay, this); // 创建定时器对象，delay指定延时
timer.start();
}
// 设置延时
public void setDelay(int delay) {
timer.setDelay(delay);
}
// 在canvas上面作画
public void paint(Graphics g) {
for (int i = 0; i < balls.length; i++) {
g.setColor(balls[i].color); // 设置颜色
balls[i].x = balls[i].left ? balls[i].x - 10 : balls[i].x + 10;
if (balls[i].x < 0 || balls[i].x >= this.getWidth()) { // 到水平方向更改方向
balls[i].left = !balls[i].left;
}
balls[i].y = balls[i].up ? balls[i].y - 10 : balls[i].y + 10;
if (balls[i].y < 0 || balls[i].y >= this.getHeight()) { // 到垂直方向更改方向
balls[i].up = !balls[i].up;
}
g.fillOval(balls[i].x, balls[i].y, 20, 20); // 画指定直径的圆
}
}
// 定时器定时执行事件
@Override
public void actionPerformed(ActionEvent e) {
repaint(); // 重画
}
// 获得焦点
@Override
public void focusGained(FocusEvent e) {
timer.stop(); // 定时器停止
}
// 失去焦点
@Override
public void focusLost(FocusEvent e) {
timer.restart(); // 定时器重启动
}
}
BallsJFrame.java
class BallsJFrame extends JFrame implements ChangeListener {
private BallsCanvas ball;
private JSpinner spinner;
public BallsJFrame() {
super("弹弹球");
this.setBounds(300, 200, 480, 360);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
Color colors[] = { Color.red, Color.green, Color.blue,
Color.magenta, Color.cyan };
ball = new BallsCanvas(colors, 100);
this.getContentPane().add(ball);
JPanel panel = new JPanel();
this.getContentPane().add(panel, "South");
panel.add(new JLabel("Delay"));
spinner = new JSpinner();
spinner.setValue(100);
panel.add(spinner);
spinner.addChangeListener(this);
this.setVisible(true);
}
@Override
public void stateChanged(ChangeEvent e) {
// 修改JSpinner值时，单击JSpinner的Up或者down按钮时，或者在JSpinner中按Enter键
ball.setDelay(Integer.parseInt("" + spinner.getValue()));
}
public static void main(String[] args) {
new BallsJFrame();
}
}
效果如下：
