各位好，小弟刚学java一个月，更是刚接触swing没几天，现遇到一些问题，希望大家能够帮忙指导下，下面的代码是学习班我们组刚开的一个项目，是做的航空公司柜员系统，我负责界面设计，因为我看了论坛上各位大大用SWING做的界面很帅~很羡慕，所以就自告奋勇接了下来，下面的代码是设置背景图片，改变外观的代码，编译无错，运行出界面，但也报了很多异常，小弟实在不知道怎么处理，望有人帮忙
package clientframe;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
/**
- @author dj2041
- @version V1.0
-
/
public class CloginFrame {
private JFrame mainFrame;
private JPanel loginJpanel;
private JLabel idJlabel;
private JLabel passwordJlabel;
private JTextField idTextField;
private JPasswordField passwordField;
private JButton enterButton;
private JButton cancerButton;
public CloginFrame() {
mainFrame=new JFrame();
idJlabel=new JLabel("工号");
idTextField=new JTextField(15);
passwordJlabel=new JLabel("密码");
passwordField=new JPasswordField(15);
enterButton=new JButton("确定");
cancerButton=new JButton("取消");
loginJpanel=new JPanel();
ImageIcon img = new ImageIcon("背景.jpg");
setBackground(mainFrame,img);
init();
eventhandler();
}
/*- @param frame 被设置的容器
-
@param img 被设置为背景的图片
*/
public void setBackground(JFrame frame,ImageIcon img){
JLabel imgLabel=new JLabel(img);//将图片放入一个JLabel中
imgLabel.setBounds(0, 0, img.getIconWidth(), img.getIconHeight());//设置图片所在的JLabel的属性
frame.getLayeredPane().add(imgLabel,new Integer(Integer.MIN_VALUE));//将图片添加到LayeredPane层
((JPanel) frame.getContentPane()).setOpaque(false);//使内容层透明
}
private void init(){
mainFrame.setLayout(null);//设置为自定义布局
mainFrame.add(loginJpanel);//添加登陆界面
loginJpanel.add(idJlabel);
loginJpanel.add(idTextField);
loginJpanel.add(passwordJlabel);
loginJpanel.add(passwordField);
loginJpanel.add(enterButton);
loginJpanel.add(cancerButton);//顺序添加组件
loginJpanel.setSize(200, 120);//设置大小
loginJpanel.setLocation(Toolkit.getDefaultToolkit().getScreenSize().width/2-120, Toolkit.getDefaultToolkit().getScreenSize().height/2+60);
//根据分辨率设置登陆界面相对位置
loginJpanel.setOpaque(false);//将登陆界面设置为透明
}
public void showMe(){mainFrame.setVisible(true);//设置frame 可见
mainFrame.setLocation(0,0);//设置frame的位置
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//设置关闭按钮命令
mainFrame.setSize(Toolkit.getDefaultToolkit().getScreenSize().width, Toolkit.getDefaultToolkit().getScreenSize().height);//根据系统分辨率设置frame大小
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");//设置外观风格
SwingUtilities.updateComponentTreeUI(mainFrame);
} catch (Exception e) {
e.printStackTrace();
}
}
public void eventhandler(){
//?????
cancerButton.addActionListener(new ActionListener(){
@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
System.exit(0);
}});
}
public static void main(String[] args) {
new CloginFrame().showMe();
}
}
异常如下：Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.plaf.synth.SynthLookAndFeel.paintRegion(SynthLookAndFeel.java:387)
at javax.swing.plaf.synth.SynthLookAndFeel.update(SynthLookAndFeel.java:351)
at javax.swing.plaf.synth.SynthRootPaneUI.update(SynthRootPaneUI.java:77)
at javax.swing.JComponent.paintComponent(JComponent.java:763)
at javax.swing.JComponent.paint(JComponent.java:1027)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5122)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:277)
at javax.swing.RepaintManager.paint(RepaintManager.java:1217)
at javax.swing.JComponent._paintImmediately(JComponent.java:5070)
at javax.swing.JComponent.paintImmediately(JComponent.java:4880)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:803)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:714)
at javax.swing.RepaintManager.seqPaintDirtyRegions(RepaintManager.java:694)
at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:128)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
