Java Swing NullPointerException

Question

paul ince 0 Newbie Poster

13 Years Ago

Hello, I am quite new to swing, and I was trying the JFrame component, when this exception occurred , just when I tried to instantiate the JFrame object. It says the following:

Exception in thread "main" java.lang.NullPointerException

at JFrameDemo.main(JFrameDemo.java:8)

and line 8 is the following

JFrame frame = new JFrame("Title");

How come the nullexc. occurs when I try to instantiate a new JFrame object?

Here's the complete code.

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


public class JFrameDemo {
	
	public static void main(String[] args) {
		JFrame frame = new JFrame("Title");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		JLabel textLabel = new JLabel("I'm a bloody label",SwingConstants.CENTER);
		textLabel.setPreferredSize(new Dimension(300,100));
		frame.getContentPane().add(textLabel,BorderLayout.CENTER);
		
		
		frame.pack();
		frame.setVisible(true);
		
	}
}

java

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Latest Post 13 Years Ago Latest Post by Stefano Mtangoo

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NormR1 563 Posting Sage

13 Years Ago

I don't see how you can get a NPE at the line of code you show.

Are you sure that the code you posted is what you are executing? Compile it again and try to execute it again.

Edited 13 Years Ago by NormR1 because: n/a

NormR1 563 Posting Sage

13 Years Ago

Execute the program in a command prompt window and copy and paste the contents of the window here.

Your program compiled and execute with no problem for me.

NormR1 563 Posting Sage

13 Years Ago

I guess there's something wrong with your java installation. Try uninstalling and reinstalling it.

javaAddict 900 Nearly a Senior Poster

13 Years Ago

At errors you get it says this:

at JFrameDemo.main(JFrameDemo.java:8)

What does it say at the line 8 of the file JFrameDemo.java. Something there is null

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paul ince 0 Newbie Poster · Answer 1 · 2010-07-16T04:11:21+00:00

I don't see how you can get a NPE at the line of code you show.
Are you sure that the code you posted is what you are executing? Compile it again and try to execute it again.

I'm positive man, that's what's running. I compiled it and ran it, that is the exception. I do not see how's that possible myself. Maybe I need to set something so I can use Java Swing? Some paths, system variables or something? I don't have a clue...

paul ince 0 Newbie Poster · Answer 2 · 2010-07-16T15:02:42+00:00

Execute the program in a command prompt window and copy and paste the contents of the window here.
Your program compiled and execute with no problem for me.

I compiled it using cmd, and when I tried to execute it this message showed up:

Exception in thread "main" java.lang.NullPointerException
        at sun.awt.FontConfiguration.getVersion(Unknown Source)
        at sun.awt.FontConfiguration.readFontConfigFile(Unknown Source)
        at sun.awt.FontConfiguration.<init>(Unknown Source)
        at sun.awt.windows.WFontConfiguration.<init>(Unknown Source)
        at sun.awt.Win32GraphicsEnvironment.createFontConfiguration(Unknown Sour
ce)
        at sun.java2d.SunGraphicsEnvironment$2.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.java2d.SunGraphicsEnvironment.<init>(Unknown Source)
        at sun.awt.Win32GraphicsEnvironment.<init>(Unknown Source)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)

        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Sou
rce)
        at java.lang.reflect.Constructor.newInstance(Unknown Source)
        at java.lang.Class.newInstance0(Unknown Source)
        at java.lang.Class.newInstance(Unknown Source)
        at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(Unknown Sour
ce)
        at java.awt.Window.init(Unknown Source)
        at java.awt.Window.<init>(Unknown Source)
        at java.awt.Frame.<init>(Unknown Source)
        at javax.swing.JFrame.<init>(Unknown Source)
        at JFrameDemo.main(JFrameDemo.java:8)

NormR1 563 Posting Sage Team Colleague · Answer 3 · 2010-07-16T18:01:18+00:00

at javax.swing.JFrame.<init>(Unknown Source)
at JFrameDemo.main(JFrameDemo.java:8)

It looks like its in the constructor for JFrame.

javaAddict 900 Nearly a Senior Poster Team Colleague Featured Poster · Answer 4 · 2010-07-16T19:04:40+00:00

It looks like its in the constructor for JFrame.

I find it hard to believe that that code could throw such exception. Don't forget that the line numbers you get from the errors have nothing to do with the line numbers that appear in the post. You shouldn't rely that a line of code here is at the exact line in the poster's java file

NormR1 563 Posting Sage Team Colleague · Answer 5 · 2010-07-16T19:09:53+00:00

Look at the stack trace.
What was called when the NPE occurred?
It looks to me like the constructor for the JFrame class was called at line 8 in the OP's program.

paul ince 0 Newbie Poster · Answer 6 · 2010-07-16T21:14:44+00:00

It's definitely the constructor of JFrame, but as it was said back on the top - there
s nothing wrong with the code. I suspected it earlier, and now a friend suggested that I try running this via NetBeans instead of Eclipse, and it succeeded. So I guess Eclipse is missing something so it can execute java swing, but why couldn't I execute it via cmd?

NormR1 563 Posting Sage Team Colleague · Answer 7 · 2010-07-16T21:20:22+00:00

You should say you are running the code from inside of an IDE.
I guess we should have asked.

You never tried it the way I suggested several posts back:

Execute the program in a command prompt window and copy and paste the WHOLE contents of the window here.

Try that and see what happens

paul ince 0 Newbie Poster · Answer 8 · 2010-07-16T21:28:50+00:00

Dude, I pasted the WHOLE contents earlier. After I compiled it, I typed "Java JFrameDemo" and the exception that I've pasted earlier occurred. Again - I used Eclipse the first time, then I tried it using cmd, as you said and it didn't work. Then I tried NetBeans and it worked. But I want it to work via cmd.

JamesCherrill 4,733 Most Valuable Poster Team Colleague Featured Poster · Answer 9 · 2010-07-16T21:44:19+00:00

Looks a lot like a Java install/config issue to me. Do you have multiple JRE installations - if so how many, where, and what versions? May be a good idea to clear it all out and just do a clean install of the latest Java

NormR1 563 Posting Sage Team Colleague · Answer 10 · 2010-07-16T22:05:29+00:00

@paul ince
I asked you to paste the WHOLE contents of the window
The whole contents shows the directory and the command line.
You edited out/left off the commmand line
the WHOLE contents of the command prompt (on Windows):

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
D:\Norms\Norms Tools>java asdf
Exception in thread "main" java.lang.NoClassDefFoundError: asdf
Caused by: java.lang.ClassNotFoundException: asdf
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: asdf. Program will exit.
D:\Norms\Norms Tools>

Stefano Mtangoo 455 Senior Poster · Answer 11 · 2010-07-16T23:14:25+00:00

For me it sounds like installation problems.
It is working fine for me. see screenshot. Which OS do you use.
I guess you should re-install JDK

Java Swing NullPointerException

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