我正在为一个类编写一个小程序,并认为代码看起来正确,我在小程序启动时收到一个空指针异常。任何帮助将不胜感激。
错误信息:
java.lang.NullPointerException
at sun.applet.AppletAudioClip.(AppletAudioClip.java:65)
at java.applet.Applet.newAudioClip(Applet.java:311)
at Lab5b.(Lab5b.java:14)
at sun.reflect.NativeConstructorAccessorImpl .newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstruct orAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingC onstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor .java:525)
在 java.lang.Class.newInstance0(Class.java:372)
在 java.lang.Class.newInstance(Class.java:325)
在 sun.applet.AppletPanel.createApplet(AppletPanel.java:795)
在 sun.applet.AppletPanel.runLoader(AppletPanel.java:724 ) 在 sun.applet.AppletPanel.run(
AppletPanel.java:378)
在 java.lang。线程运行(线程.java:722)
代码:
import javax.swing.*;
import java.awt.event.*;
import java.net.URL;
import java.applet.*;
import java.awt.*;
public class Lab5b extends JApplet {
private AudioClip audioClip;
public Lab5b() {
add(new ImagePanel());
URL urlForAudio = getClass().getResource("audio/us.mid");
audioClip = Applet.newAudioClip(urlForAudio);
audioClip.loop();
}
public void start() {
if (audioClip != null) audioClip.loop();
}
public void stop() {
if (audioClip != null) audioClip.stop();
}
/** Main method */
public static void main(String[] args) {
// Create a frame
JFrame frame = new JFrame("Lab 5");
// Create an instance of the applet
Lab5b applet = new Lab5b();
applet.init();
// Add the applet instance to the frame
frame.add(applet, java.awt.BorderLayout.CENTER);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Display the frame
frame.setSize(200, 660);
frame.setVisible(true);
}
}
class ImagePanel extends JPanel {
private ImageIcon imageIcon = new ImageIcon("image/us.gif");
private Image image = imageIcon.getImage();
private int y = 550;
public ImagePanel() {
Timer timer = new Timer(120, new TimerListener());
timer.start();
}
class TimerListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
increaseY();
}
}
public void increaseY() {
if (y > 0) {
y--;
repaint();
}
}
/** Draw image on the panel */
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (image != null) {
g.fillRect(0, 0, 10, 660);
g.drawImage(image, 11, y, 160, 84, this);
}
}
}