image loading using a JFileChooser into a JFrame
Solution 1
The value of img
will only have a real value after the user click the button and chooses the file to display. Until this time, the value of img
is null
, so when it continues through your method and calls the line ImageIcon icon=new ImageIcon(img);
, it is trying to create an ImageIcon
object for null
.
To correct this, you should only be creating the ImageIcon
when the user has chosen the file. Here is a change that should be closer to working correctly. (see the comments //ADDED
and //REMOVED
in the code below to see the changes...
...
class power extends JFrame {
JFileChooser chooser;
BufferedImage img;
JButton button,button2;
JFrame comp;
String filename;
File file ;
JLabel label; // ADDED
public power() {
...
public void actionPerformed(ActionEvent e) {
if (e.getSource()==button) {
chooser.showOpenDialog(null);
file = chooser.getSelectedFile();
try {
img=ImageIO.read(file);
ImageIcon icon=new ImageIcon(img); // ADDED
label.setIcon(icon); // ADDED
Dimension imageSize = new Dimension(icon.getIconWidth(),icon.getIconHeight()); // ADDED
label.setPreferredSize(imageSize); // ADDED
label.revalidate(); // ADDED
label.repaint(); // ADDED
}
catch(IOException e1) {}
}
if (e.getSource()==button2){
comp.setVisible(true);
}
}
};
//ImageIcon icon=new ImageIcon(img); // REMOVED
//JLabel label=new JLabel(icon); // REMOVED
label = new JLabel(); // ADDED
JPanel secpanel=new JPanel();
...
To explain what I've changed...
- The
label
will now be created as an emptyJLabel
when you first start the program. It is also stored as a global variable so we can access it later - When the button is clicked, the
img
is created, as before, and then it is loaded into yourlabel
usingsetIcon();
- The label is resized, then
revalidate()
andrepaint()
to make sure that the image is drawn after it is set.
Solution 2
The ImageIO.read
is only executed when that specific JButton
is pressed. That is because it's inside the ActionListener
. Because of this, img
is null which causes a NullPointerException
when ImageIcon icon=new ImageIcon(img)
is executed.
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Admin
Updated on June 04, 2022Comments
-
Admin about 2 years
I am trying to write a code that displays an image selected using a JFileChooser into another JFrame .I tried the following code below but only got the following errors.
Exception in thread "main" java.lang.NullPointerException at javax.swing.ImageIcon.<init>(ImageIcon.java:228) at power.<init>(fCGUI.java:53) at fCGUI.main(fCGUI.java:11)
Here is the code:
import javax.imageio.ImageIO; import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.awt.image.BufferedImage; import java.io.File; import java.io.IOException; public class fCGUI { public static void main(String []args) { power p=new power(); p.setVisible(true); } } class power extends JFrame { JFileChooser chooser; BufferedImage img; JButton button,button2; JFrame comp; String filename; File file ; public power() { setSize(450,450); panel.setLayout(new BorderLayout()); JPanel panel=new JPanel(); getContentPane().add(panel); button =new JButton("press"); panel.add(button,BorderLayout.NORTH); chooser = new JFileChooser(); ActionListener action=new ActionListener() { public void actionPerformed(ActionEvent e) { if (e.getSource()==button) { chooser.showOpenDialog(null); file = chooser.getSelectedFile(); try { img=ImageIO.read(file); } catch(IOException e1) {} } if (e.getSource()==button2) { comp.setVisible(true); } } }; ImageIcon icon=new ImageIcon(img); JLabel label=new JLabel(icon); JPanel secpanel=new JPanel(); comp=new JFrame(); comp.setSize(650,500); comp.setLayout(new BorderLayout()); comp.setTitle("View Report"); JRootPane compPane=comp.getRootPane(); Container contePane=compPane.getContentPane(); contePane.add(secpanel); secpanel.add(label,BorderLayout.CENTER); button2=new JButton("access"); button2.addActionListener(action); button.addActionListener(action); panel.add(button2,BorderLayout.SOUTH); } }