Java swing, cannot get an image to work

Question

I have wrote a simple program just to draw an image, I cannot get it to work at all. It should just show 1 picture within a pane within a frame. p.s. there are prolly imports i do not need, i tried many different things.

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Panel;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import javax.swing.*;


import javax.imageio.ImageIO;

public class ShowImage {
private Graphics g;
private BufferedImage lionImage=null;
private JFrame frame;
private JPanel totalGUI,values;

 public static void main(String[] args) {
       SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }

   });
   }
 public JPanel createContentPane(){
     totalGUI = new JPanel();


        totalGUI.setLayout(null);

        values = new JPanel();
        values.setLayout(null);
        values.setLocation(10, 10);
        values.setSize(490, 290);
        values.setBackground(Color.WHITE);
        totalGUI.add(values);
        getImage();
        Graphics g = values.getGraphics();

        g.drawImage(lionImage,100,100,null);

        totalGUI.setOpaque(true);
        return totalGUI;
 }


    private static void createAndShowGUI() {
        JFrame.setDefaultLookAndFeelDecorated(true);
        JFrame frame = new JFrame("Calculator");

        ShowImage demo = new ShowImage();
        frame.setContentPane(demo.createContentPane());

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(500, 300);
        frame.setVisible(true);

}

void getImage(){
    try{
    lionImage =ImageIO.read(new File("imgres.jpg"));// *see note
    }catch (IOException e){}
    }

}

I get the error. Which I have no idea what the problem is.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at ShowImage.createContentPane(ShowImage.java:43)
at ShowImage.createAndShowGUI(ShowImage.java:55)
at ShowImage.access$0(ShowImage.java:50)
at ShowImage$1.run(ShowImage.java:23)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(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.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)

Where is the image stored? If its within the jar see [this answer](http://stackoverflow.com/questions/13796331/jar-embedded-resources-nullpointerexception/13797070#13797070). Also see [here](http://stackoverflow.com/questions/12996501/how-to-display-an-image-in-a-frame/12996718#12996718) for how to paint image to JPanel.BTW Where is your `ex.printStackTrace()` within catch block? always use it — David Kroukamp, Feb 11 '13 at 16:11

score 1 · Answer 1 · edited May 23 '17 at 11:50

1

This is because your g is null. This happens when the path to the JPanel is not yet displayed on screen.

In order to draw an image inside a JPanel, you would usually create a new class that extends JPanel and override its paintComponent(Graphics g) method. See this for an example, just that you would need to call the drawImage() method.

I suggest you never catch an Exception and don't handle it in any way. You do this in the getImage() method where you try to load the image.

edited May 23 '17 at 11:50

Community

1
1

answered Feb 11 '13 at 12:35

Dan D.

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I am using the method suggested to me by my lecturer. How do I fix the path? – user1817988 Feb 11 '13 at 12:42
It is either g or lionImage null. – Dan D. Feb 11 '13 at 12:59
1

@user1817988 Get a new lecturer. You should never use the getGraphics method directly. Instead create a custom component, override its paintComponent method and render the image within it. Alternatively, use a ImageIcon and apply it to a JLabel – MadProgrammer Feb 11 '13 at 20:01

score 1 · Answer 2 · answered Feb 11 '13 at 12:56

public static void main (String [] args) throws Exception 
{
    final BufferedImage lionImage = ImageIO.read (new File ("imgres.jpg"));

    JComponent image = new JComponent () 
    {
        @Override
        protected void paintComponent (Graphics g) 
        {
            super.paintComponent (g);

            g.drawImage (lionImage, 0, 0, null);
        }

        @Override
        @Transient
        public Dimension getPreferredSize () 
        {
            return new Dimension (lionImage.getWidth (), lionImage.getHeight ());
        }
    };
    image.setOpaque (true);

    JFrame frame = new JFrame ("Image");
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
    frame.getContentPane ().setLayout (new BorderLayout ());
    frame.getContentPane ().add (image, BorderLayout.CENTER);
    frame.pack ();
    frame.setVisible (true);
}

A `JLabel` (with `ImageIcon` displaying the image) could do all that `JComponent` seems to be doing. `g.drawImage (lionImage, 0, 0, null);` It would also tend to paint the image using an image observer, like `this` e.g. `g.drawImage (lionImage, 0, 0, this);`. — Andrew Thompson, Feb 11 '13 at 21:19

Java swing, cannot get an image to work

2 Answers2