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Thread: Problem altering text in JLabel
- 06-28-2009, 03:12 PM #1
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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:
I'm sure it is something forehead-slappingly obvious.Java Code:if (actionCommand.equalsIgnoreCase("press")) { bTotal++; bCounterString = ("Count: " + Integer.toString(bTotal)); bCounter.setText(bCounterString);
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)
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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?
- 06-29-2009, 12:35 AM #3
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