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  1. #1
    porchrat is offline Senior Member
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    Default Problem altering text in JLabel

    I'm trying to create a little swing program consisting of just a single JFrame and some buttons and some labels. It is just for fun and I thought it would be easy, but I've run into a strange problem that I just can't figure out.

    Essentially when the user clicks a button a JLabel has a number that needs to increment by 1 (it essentially displays a value that indicates how many times that button has been pressed).

    Problem is that when I click the button the JLabel_name.setText("String" + Integer.toString(newly_incremented_integer) creates a stack trace with what looks like a NullPointerException.

    Even when I try to use the JLabel.getText() method it throws the stack trace. Why would this happen?

    This is the section of code in the Listener that deals with that button:

    Java Code:
    if (actionCommand.equalsIgnoreCase("press"))
    			{
    				bTotal++;
    					
    				bCounterString = ("Count: " + Integer.toString(bTotal));
    					bCounter.setText(bCounterString);
    I'm sure it is something forehead-slappingly obvious.

    Here is the stack trace:
    Java Code:
    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    	at test.MyWindow$mainListener.actionPerformed(MyWindow.java:132)
    	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
    	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
    	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    	at java.awt.Component.processMouseEvent(Component.java:6041)
    	at javax.swing.JComponent.processMouseEvent(JComponent.java:3265)
    	at java.awt.Component.processEvent(Component.java:5806)
    	at java.awt.Container.processEvent(Container.java:2058)
    	at java.awt.Component.dispatchEventImpl(Component.java:4413)
    	at java.awt.Container.dispatchEventImpl(Container.java:2116)
    	at java.awt.Component.dispatchEvent(Component.java:4243)
    	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
    	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
    	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
    	at java.awt.Container.dispatchEventImpl(Container.java:2102)
    	at java.awt.Window.dispatchEventImpl(Window.java:2440)
    	at java.awt.Component.dispatchEvent(Component.java:4243)
    	at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
    	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
    	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
    	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    	at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

  2. #2
    Fubarable's Avatar
    Fubarable is offline Moderator
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    Default

    My guess (without seeing more code, it can only be a guess), is that the JLabel you are trying to change the text on is not the one being displayed. Have you declared the JLabel twice per chance?

  3. #3
    porchrat is offline Senior Member
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    Default

    Quote Originally Posted by Fubarable View Post
    My guess (without seeing more code, it can only be a guess), is that the JLabel you are trying to change the text on is not the one being displayed. Have you declared the JLabel twice per chance?
    You are 100% correct sir! I had indeed declared it twice. Stupid error.

    Thank you so much for your help.:D

  4. #4
    Fubarable's Avatar
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