Graphics错误Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
zwyjn 2006-09-07 10:59:22 当我运行下面的程序时,出现标题出现的错误
import javax.swing.SwingUtilities;
import java.awt.BorderLayout;
import javax.swing.JPanel;
import javax.swing.JFrame;
import javax.swing.JLabel;
import java.awt.*;
public class Main extends JFrame {
private static final long serialVersionUID = 1L;
private JPanel jContentPane = null;
private JLabel jLabel = null;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
Main thisClass = new Main();
thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
thisClass.setVisible(true);
}
});
}
public Main() {
super();
initialize();
}
private void initialize() {
Graphics g;
this.setSize(300, 200);
this.setContentPane(getJContentPane());
g=jContentPane.getGraphics();
g.setColor(Color.black);
g.fillRect(0, 0, 20, 20);
this.setTitle("JFrame");
}
private JPanel getJContentPane() {
if (jContentPane == null) {
jLabel = new JLabel();
jLabel.setText("JLabel");
jContentPane = new JPanel();
jContentPane.setLayout(new BorderLayout());
jContentPane.add(jLabel, BorderLayout.CENTER);
}
return jContentPane;
}
}
错误提示:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at com.zw.Main.initialize(Main.java:51)
at com.zw.Main.<init>(Main.java:38)
at com.zw.Main$1.run(Main.java:26)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)