Null pointer exception JLabel

Question

Why do I get a NullPointerException when I try and run this on a label:

JLabel player1CurrentScore = new JLabel("" + matchPlay.returnPL1GamesWon(),
                                        JLabel.CENTER);

Is it because I cannot have two strings concatenated like this?

Ideally, I am trying to set the label as the score of the player so it can be incremented correctly as and when is needed.

Here is my Exception stackdump:

java.lang.NullPointerException
at GUI.makeFrame(GUI.java:71)
at GUI.<init>(GUI.java:28)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at bluej.runtime.ExecServer$3.run(ExecServer.java:808)

Aside: If matchPlay.returnPL1GamesWon() is numeric, the better way to do this in recent JVMs is String.valueOf(matchPlay.returnPL1GamesWon()) and to avoid ""+ to "stringize" a number. As others said, the NullPointerException MUST be from matchPlay being null. — Eddie
– Eddie, Commented Mar 16, 2009 at 14:50

brabster · Accepted Answer · 2009-03-16 15:02:16Z

3

Based on the information in the question: the reference matchPlay is null.

Updated: Given the info that matchPlay cannot be null, then the method that is called on matchPlay must be throwing the exception. Check the stack trace for the previous method call, should help to pinpoint the problem.

edited Mar 16, 2009 at 15:02

answered Mar 16, 2009 at 14:44

brabster

43.7k29 gold badges150 silver badges189 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Roberto Duran Over a year ago

it cant be tho becuase some of the other methods from matchPlay are working, i have the following private Game matchPlay <constructor> matchPlay = new Game() so how can it be null?

brabster Over a year ago

Ah. You didn't say that. In that case, see @Paul Tomblin's answer below.

Paul Tomblin · Accepted Answer · 2009-03-16 15:16:28Z

3

There's nothing there that will cause a null pointer exception unless matchPlay is null or matchPlay.returnPL1GamesWon() throws a null pointer exception itself.

Update: Based on the fact that the exception is coming from GUI.makeFrame, I have to ask if you've actually got a graphic display? Is this a command line app, a Swing app, or an Applet? It looks like you're trying to create a JLabel without a graphics context.

edited Mar 16, 2009 at 15:16

answered Mar 16, 2009 at 14:44

Paul Tomblin

184k59 gold badges324 silver badges412 bronze badges

4 Comments

brabster Over a year ago

I think if matchPlay.returnPL1GamesWon() returns null, it will just print 'null', not throw an NullPointerException?

Eddie Over a year ago

Yes, what Brabster said. However, it's possible that matchPlay.returnPL1GamesWon() is itself throwing a NullPointerException.

Roberto Duran Over a year ago

if i new how to use this site i wouldo post the error message exactly <stacktrace or whatever its called> however i did leave a comment above saying how it cant be possible

Paul Tomblin Over a year ago

@Roberto, you should be able to edit your question - just click the "edit" button below it.

Ruwan Pathirana · Accepted Answer · 2022-09-17 10:03:07Z

1

Change to:

player1CurrentScore = new JLabel("" + matchPlay.returnPL1GamesWon(),
                                    JLabel.CENTER);

Moreover then you can add Jlabel variable in public class if error occurred,

    public class YourClass{
             private JLabel player1CurrentScore;
    }

answered Sep 17, 2022 at 10:03

Ruwan Pathirana

1872 silver badges11 bronze badges

Comments

Roberto Duran · Accepted Answer · 2009-03-16 15:15:26Z

0

i have managed to answer it,

it was the order of which i was assigning fields in the constructor

sorry for the bother

thanks everyone

answered Mar 16, 2009 at 15:15

Roberto Duran

Collectives™ on Stack Overflow

Null pointer exception JLabel

4 Answers 4

2 Comments

4 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

4 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related