我正在尝试从目录加载图像，并在单击其中一个按钮时显示它们。不幸的是，我仍然收到此错误：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at picsFrom.dir.SSGui.NextActionPerformed(SSGui.java:95)
at picsFrom.dir.SSGui.access$200(SSGui.java:11)
at picsFrom.dir.SSGui$3.actionPerformed(SSGui.java:60)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6539)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6304)
at java.awt.Container.processEvent(Container.java:2239)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2297)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476)
at java.awt.Container.dispatchEventImpl(Container.java:2283)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
at java.awt.EventQueue$4.run(EventQueue.java:733)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
Main.java
package picsFrom.dir;
import java.awt.*;
public class Main {
public static void main(String args[]) {
image i = new image();
i.ListFiles();
String[] cmb = i.combined;
System.out.println(i.ListFiles().length);
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
new SSGui().setVisible(true);
}
});
}
}
image.java
package picsFrom.dir;
import java.io.File;
import java.io.FilenameFilter;
public class image {
private String[] namesPNG, namesJPG, namesGIF;
public String[] combined;
public String[] ListFiles() {
File dir = new File("C:\\Users\\John\\Pictures\\");
namesPNG = dir.list(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.endsWith(".png");
}
});
namesJPG = dir.list(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.endsWith(".jpg");
}
});
namesGIF = dir.list(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.endsWith(".gif");
}
});
combined = new String[namesPNG.length + namesJPG.length + namesGIF.length];
int combLenght = namesPNG.length + namesJPG.length;
System.arraycopy(namesPNG, 0, combined, 0, namesPNG.length);
System.arraycopy(namesJPG, 0, combined, namesPNG.length, namesJPG.length);
System.arraycopy(namesGIF, 0, combined, combLenght, namesGIF.length);
return combined;
}
}
SSGui.java
package picsFrom.dir;
import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
public class SSGui extends javax.swing.JFrame {
public SSGui() {
initComponents();
}
@SuppressWarnings("unchecked")
private void initComponents() {
iP = new javax.swing.JPanel() {
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawImage(img, 0, 0, this.getWidth(), this.getHeight(), this);
System.out.println(img);
}
/*public void setImage(BufferedImage img) {
this.img = img;
repaint();
}*/
};
Prev = new javax.swing.JButton();
Next = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
javax.swing.GroupLayout iPLayout = new javax.swing.GroupLayout(iP);
iP.setLayout(iPLayout);
iPLayout.setHorizontalGroup(
iPLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 0, Short.MAX_VALUE)
);
iPLayout.setVerticalGroup(
iPLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 450, Short.MAX_VALUE)
);
Prev.setText("Prev");
Prev.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
PrevActionPerformed(evt);
}
});
Next.setText("Next");
Next.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
NextActionPerformed(evt);
}
});
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
.addComponent(iP, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(layout.createSequentialGroup()
.addComponent(Prev, javax.swing.GroupLayout.PREFERRED_SIZE, 250, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(Next, javax.swing.GroupLayout.PREFERRED_SIZE, 244, javax.swing.GroupLayout.PREFERRED_SIZE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(iP, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(Prev, javax.swing.GroupLayout.DEFAULT_SIZE, 44, Short.MAX_VALUE)
.addComponent(Next, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addGap(0, 0, 0))
);
Next.getAccessibleContext().setAccessibleDescription("");
pack();
}// </editor-fold>
private void NextActionPerformed(java.awt.event.ActionEvent evt) {
int cL = i.ListFiles().length;
try {
for (int i = cL; cL > -1; i--) {
img = ImageIO.read(new File("C:\\Users\\John\\Pictures\\" + cmb[i]));
}
} catch (IOException ex) {}
//iP.setImage(img);
}
private void PrevActionPerformed(java.awt.event.ActionEvent evt) {
int cL = i.ListFiles().length;
try {
for (int i = 0; i < cL; i++) {
img = ImageIO.read(new File("C:\\Users\\John\\Pictures\\" + cmb[i]));
}
} catch (IOException ex) {}
//iP.drawImage(img);
}
// Variables declaration - do not modify
private javax.swing.JButton Next;
private javax.swing.JButton Prev;
//private JLabel image;
image i = new image();
//imgPanel iP = new imgPanel();
private BufferedImage img;
String[] cmb = i.combined;
private javax.swing.JPanel iP;
}
有人可以告诉我我做错了什么吗？我不知道该如何解决。 我是新手，使用的是IntelliJ Idea，但是UI来自NetBeans。 预先感谢！