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，我得到一个NullPointer错误。当我到达setIcon代码时，它会中断
/**
* 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);
}
这不起作用？
我尝试在下面进行修复，但我仍然会得到一长串错误
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)
答案 0 :(得分：2)
我的猜测是，您已将picPanel声明为类成员。 JLabel picPanel（位于底部） 是您setIcon中mouseClicked引用的那个。如果没有类成员picPanel，则会导致编译错误，因为在尝试访问picPanel之前需要声明本地mouseClicked。
移动JLabel picPanel = new JLabel（“”）;在添加侦听器之前，可以解决问题。并摆脱setIcon(null)。但话说回来，我不知道你的代码中还有什么用picPanel试图做的，所以你可能想要摆脱本地声明，因为它影响了类成员。所以基本上不是
JLabel picPanel = new JLabel();
searchButton.addMouseListener(new MouseAdapter()
使用
picPanel = new JLabel();
searchButton.addMouseListener(new MouseAdapter()
以下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);
}
}