我试图从某人的计算机加载文件,然后将其作为图标放入标签中。当我尝试运行它时,出现NullPointer错误。当我到达setIcon代码时会中断
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
TheChooser frame = new TheChooser();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public TheChooser() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JButton searchButton = new JButton("Search Picture");
searchButton.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent arg0) {
FileFilter filter = new FileNameExtensionFilter("JPEG file", "jpg", "jpeg");
fc.setFileFilter(filter);
int response = fc.showOpenDialog(null);
try{
if (response == JFileChooser.APPROVE_OPTION) {
String pathName = fc.getSelectedFile().getPath();
JOptionPane.showMessageDialog(null, pathName);
ImageIcon icon = new ImageIcon(pathName);
picPanel.setIcon(icon);
} else {
JOptionPane.showMessageDialog(null, "Feel Free to Look Later");
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
searchButton.setBounds(141, 11, 139, 23);
contentPane.add(searchButton);
JLabel picPanel = new JLabel("");
picPanel.setIcon(null);
picPanel.setBounds(10, 58, 414, 192);
contentPane.add(picPanel);
}
怎么办呢?
我尝试进行以下修复,但仍然出现了很多错误
java.lang.NullPointerException
at chooser.TheChooser$2.mouseClicked(TheChooser.java:70)
at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
java.lang.NullPointerException
at chooser.TheChooser$2.mouseClicked(TheChooser.java:70)
at java.awt.AWTEventMulticaster.mouseClicked(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
最佳答案
我的猜测是,您已将picPanel
声明为类成员。 JLabel picPanel
(朝下)不是您在setIcon
中从mouseClicked
引用的那个。如果没有类成员picPanel
,则将导致编译错误,因为在尝试通过picPanel
对其进行访问之前,必须先声明本地mouseClicked
。
移动JLabel picPanel = new JLabel(“”);在添加侦听器之前,可能会解决此问题。并摆脱setIcon(null)
。但是话又说回来,我不知道您在代码中还想使用picPanel
做些什么,因此您可能希望摆脱局部声明,因为它使类成员蒙上了阴影。所以基本上不是
JLabel picPanel = new JLabel();
searchButton.addMouseListener(new MouseAdapter()
采用
picPanel = new JLabel();
searchButton.addMouseListener(new MouseAdapter()
这是完整程序中的修复程序
public class TheChooser extends JFrame {
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
TheChooser frame = new TheChooser();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
private JPanel contentPane;
private JFileChooser fc = new JFileChooser();
private JLabel picPanel;
public TheChooser() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
//JLabel picPanel = new JLabel("");
picPanel = new JLabel();
JButton searchButton = new JButton("Search Picture");
searchButton.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent arg0) {
FileFilter filter = new FileNameExtensionFilter("JPEG file", "jpg", "jpeg");
fc.setFileFilter(filter);
int response = fc.showOpenDialog(null);
try {
if (response == JFileChooser.APPROVE_OPTION) {
String pathName = fc.getSelectedFile().getPath();
JOptionPane.showMessageDialog(null, pathName);
ImageIcon icon = new ImageIcon(pathName);
picPanel.setIcon(icon);
} else {
JOptionPane.showMessageDialog(null, "Feel Free to Look Later");
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
searchButton.setBounds(141, 11, 139, 23);
contentPane.add(searchButton);
picPanel.setBounds(10, 58, 414, 192);
contentPane.add(picPanel);
}
}