Simple slideshow help

Question

Hi, I want to create a simple slideshow but my app fails with a NPE when it attempts to read in the first image.
import javax.swing.JFrame;
import javax.swing.JFileChooser;
import java.io.*;
import java.awt.*;
import java.awt.image.*;
import javax.swing.*;
import java.awt.image.BufferedImage;
import java.util.Vector;
import java.awt.Graphics;
public class Main extends JPanel implements Runnable
    private static Vector imagesArray;
    private static volatile Image currentImage;
    private static volatile boolean isInterrupted=false;
    private String strCurrentDir=System.getProperty("user.dir");
    //gets the current working directory
    private JFrame frame;
    private JPanel panel;
    public static void main(String[] args)
        new Main();
    public Main()
        frame = new JFrame();
        panel = new JPanel();
        frame.getContentPane().add(panel);
        getImages();    //prompt the user to select images
        Thread animationThread = new Thread(this);
        animationThread.start();
    public void getImages()
        String strTextFieldContents="";
        //open file chooser so the user can find the file
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setCurrentDirectory(new File(strCurrentDir));
        //sets file choose to use the current working directory
        fileChooser.addChoosableFileFilter((new ImagesFilter()));
        fileChooser.setDialogTitle("Please select image files");
        int returnVal = fileChooser.showOpenDialog(new JFrame());
        if (returnVal == JFileChooser.APPROVE_OPTION)
                File temp=fileChooser.getSelectedFile();
                strTextFieldContents=temp.getAbsolutePath();
                imagesArray.add((String)strTextFieldContents);
        else{}
        imagesArray.trimToSize();
    public void run()
        while(isInterrupted==false)
            for(int i=0; i<imagesArray.size(); i++)
                try
                    Thread.sleep(200);   //display the image for 200ms at a time
                catch(InterruptedException e)
                    System.out.println("Interrupted");
                // If the Toolkit cannot find the file or load the data it
                // gives no warning. You must check on the loading status
                // for yourself.
                MediaTracker mt = new MediaTracker(this);
                mt.addImage(currentImage, 0);
                try
                    mt.waitForID(0);
                catch(InterruptedException e)
                    System.out.println("media tracker interrupted");
                        int status = mt.statusAll(false);
                if((status & MediaTracker.COMPLETE) != MediaTracker.COMPLETE)
                    System.out.println("status = " + status);
                // getImage is asynchronous, ie, it doesn't wait for the
                // image data to load. So you may need to stop to load it.
                Toolkit toolkit = Toolkit.getDefaultToolkit();
                String strImageLoc=(String)imagesArray.elementAt(i);
                //currentImage = toolkit.getImage("Cuboid_Obstacle.jpg");
                currentImage = toolkit.getImage(strImageLoc);
                currentImage=(BufferedImage)imagesArray.elementAt(i);
                panel.repaint();
    public void paintComponent(Graphics g)
        //super.paintComponent(g);
        Toolkit.getDefaultToolkit().sync();
        if (currentImage!=null)
            g.drawImage (currentImage, 0, 0, this);
}

Answer 1

The compiler tells you which line of your code generates the NullPointerException. Analyze that line to determine which of your references may be null.
Hint: Declaring a variable reference does not initialize it!
Then deal with the ClassCastException the same way.
db