Question

I’ve been programming in Java for a little while now but have never really done much with the swing packages. I am currently designing a GUI for an A.I. call and response program despite the relative complexity (for me at least) of the rest of what I have been doing, this image loading problem, which seemed extremely simple to implement is stumping me.

The below classes work if not in a package, which is what really confuses me. I’ve tried several different implementation suggestions (one from Head First Java, one from the docs.oracle.com tutorials and another using what http://leepoint.net/notes-java/GUI-lowlevel/graphics/45imageicon.html suggests).

package CaRII;


import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class P{


public static void main(String [] args){

    P p = new P();
    p.go();

}
public void go(){

    JFrame frame = new JFrame("CaRRI: Call and Response Intelligent Improviser");
    PBackground mainPanel = new PBackground();

    frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

    frame.setSize(800,500);
    frame.setVisible(true);


}

}

package CaRII;
import java.awt.*;
import javax.swing.*;

public class PBackground extends JPanel{

public Image backgroundImage;


public PBackground(){

    backgroundImage = Toolkit.getDefaultToolkit().createImage("CaRIIBackGround.jpg");

}

public PBackground(LayoutManager layout){

    backgroundImage = Toolkit.getDefaultToolkit().createImage("CaRIIBackGround.jpg");

}
public void paint(Graphics g){

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

Like I said the strange thing is that it doesn’t display the image if these two classes are in package CaRRI; but if I compile and run them without the package declaration they run fine(albiet the image not loading until the window resizes… but i have seen solutions online for that so I will be able to sort that once I get it loading within the package). I have been writing in XCode and JEdit and the image is stored within the package folder inside source (/src/CaRII/P.java … /src/CaRII/CaRIIBackGround.jpg), I have also tried storing the image in a resources folder within /src/ and using

ImageIcon(getClass().getResource("/resources/CaRIIBackGround.jpg)).getImage(); 

but that that causes another error when run

Exception in thread "main" java.lang.NullPointerException
at javax.swing.ImageIcon.<init>(ImageIcon.java:181)
at CaRII.PBackground.<init>(PBackground.java:19)
at CaRII.P.go(P.java:21)
at CaRII.P.main(P.java:15)

Any help would be much appreciated as despite its simplicity this has been stumping me all morning and I have a lot of other classes to write.

Thanks
(Heres the image(im a new user so i cant post images but this is a link to it))
http://imageshack.us/photo/my-images/189/cariibackground.jpg

Answer 1

package CaRII;

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
import java.net.URL;
import javax.imageio.ImageIO;

public class P{

    public static void main(String [] args){
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                P p = new P();
                p.go();
            }
        });
    }

    public void go(){
        try {
            JFrame frame = new JFrame("CaRRI: Call and Response Intelligent Improviser");
            frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            PBackground mainPanel = new PBackground();

            frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

            //frame.setSize(800,500);
            frame.pack();
            frame.setMinimumSize(frame.getSize());
            frame.setLocationByPlatform(true);
            frame.setVisible(true);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }
}

class PBackground extends JPanel{

    public BufferedImage backgroundImage;


    public PBackground() throws Exception {
        URL url = new URL("http://desmond.imageshack.us/Himg189/" + 
            "scaled.php?server=189&filename=cariibackground.jpg&res=medium");
        // You might form that URL using something like..
        //URL url = this.getClass().getResource("/CaRIIBackGround.jpg");

        backgroundImage = ImageIO.read(url);
        Dimension d = new Dimension(
            backgroundImage.getWidth(),
            backgroundImage.getHeight());
        setPreferredSize(d);
    }

    /*  What was this supposed to achieve?
    public PBackground(LayoutManager layout){
        backgroundImage = Toolkit.getDefaultToolkit().createImage("CaRIIBackGround.jpg");
    }
    */

    // Don't override paint() in a Swing panel!
    //public void paint(Graphics g){
    @Override
    public void paintComponent(Graphics g) {
        // USE the ImageObserver!
        //g.drawImage(backgroundImage,0,0,null);
        g.drawImage(backgroundImage,0,0,getWidth(),getHeight(),this);
    }
}