Thread: Can somone please check my code???

keep getting ERROR in eclipse

Exception in thread "main" java.lang.NullPointerException
at com.jbooktrader.platform.util.MessageDialog.showEx ception(MessageDialog.java:23)
at com.jbooktrader.platform.startup.JBookTrader.main( JBookTrader.java:62)





First page for this first message
---------------------------------------------------

package com.jbooktrader.platform.util;
 
import com.jbooktrader.platform.model.*;
import com.jbooktrader.platform.startup.*;
 
import javax.swing.*;
 
/**
 * Utility class to display message and error dialogs.
 */
public class MessageDialog {
 
    public static void showMessage(String msg) {
        JOptionPane.showMessageDialog(null, msg, JBookTrader.APP_NAME, JOptionPane.INFORMATION_MESSAGE);
    }
 
    public static void showError(String msg) {
        JOptionPane.showMessageDialog(null, msg, JBookTrader.APP_NAME, JOptionPane.ERROR_MESSAGE);
    }
 
    public static void showException(Throwable t) {
        showError(t.getMessage());
        Dispatcher.getInstance().getEventReport().report(t);
    }
}

second page-------------------------------------------------------------------

package com.jbooktrader.platform.startup;
 
import com.jbooktrader.platform.model.*;
import com.jbooktrader.platform.util.*;
 
import javax.swing.*;
import java.io.*;
import java.nio.channels.*;
 
 
/**
 * Application starter.
 */
public class JBookTrader {
    public static final String APP_NAME = "JBookTrader";
    public static final String VERSION = "8.07";
    public static final String RELEASE_DATE = "January 9, 2012";
    private static String appPath;
 
    /**
     * Instantiates the necessary parts of the application: the application model,
     * views, and controller.
     */
    private JBookTrader() throws JBookTraderException {
        try {
            Dispatcher.getInstance().setReporter();
            for (UIManager.LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (Exception e) {
            throw new JBookTraderException(e);
        }
        new MainFrameController();
    }
 
    /**
     * Starts JBookTrader application.
     *
     * @param args
     */
    public static void main(String[] args) {
        try {
            File file = new File(System.getProperty("user.home"), APP_NAME + ".tmp");
            FileChannel channel = new RandomAccessFile(file, "rw").getChannel();
 
            if (channel.tryLock() == null) {
                MessageDialog.showMessage(APP_NAME + " is already running.");
                return;
            }
 
            if (args.length != 1) {
                String msg = "Exactly one argument must be passed. Usage: JBookTrader <JBookTraderDirectory>";
                throw new JBookTraderException(msg);
            }
            appPath = args[0];
            new JBookTrader();
        } catch (Throwable t)
        {
            MessageDialog.showException(t);
        }
    }
 
    public static String getAppPath() {
        return appPath;
    }
 
}

My program arguments are on the file location and

vm argumnets are

-Xmx256M


any help??

Thank you!!!!

Exception in thread "main" java.lang.NullPointerException
at com.jbooktrader.platform.util.MessageDialog.showEx ception(MessageDialog.java:23)
at com.jbooktrader.platform.startup.JBookTrader.main( JBookTrader.java:62)

A NullPointerException occurs when you use a variable or expression as if it had a non null value (eg call a method on it) when it is really null.

The stack trace is saying that this happens on line 23 of MessageDialog.java, and what you have to do is find the variable or expression that is null. Guessing that problem occurs in the showException() method (I could be wrong) you would use System.out.println() to examine the values of variables and expressions you are "dereferencing" with method calls:

public static void showException(Throwable t) {
    System.out.println("At showException t=" + t);
    showError(t.getMessage());
    System.out.println("Dispatcher instance is " + Dispatcher.getInstance());
    System.out.println("Event report is " + Dispatcher.getInstance().getEventReport());
    Dispatcher.getInstance().getEventReport().report(t);
}

Once you have found out which thing is null you need to go back through your code to where you thought you had given it a non null value and figure out why that didn't happen.

---

If I'm wrong in my guess, say which line 23 really is. But the approach remains the same: use System.out.println() to examine everything that might possibly be null, then go back through your code to see how come it ended up null.