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Thread: Problem with ItemListener.... help pleas

  1. #1
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    Lightbulb Problem with ItemListener.... help pleas

    My problem is with ItemListener I'm not sure why it is not working. Well I'm trying to split the ItemListener
    into two class.

    in the main class I have this

    final JCheckBox whole_C_CheckBox = new JCheckBox("Whole");
    whole_C_CheckBox.addItemListener(new CheckBox(whole_C_QTextField, whole_C_WTextField, whole_C_PTextField));
    whole_C_CheckBox.setVerticalAlignment(SwingConstants.BOTTOM);
    whole_C_CheckBox.setHorizontalAlignment(SwingConstants.LEFT);
    whole_C_CheckBox.setBounds(12, 66, 113, 25);
    chikenPanel.add(whole_C_CheckBox);

    In the other class I have

     
    public class CheckBox implements ItemListener{
     
     
     
    	private JTextField q;
    	private JTextField p;
    	private JTextField w;
    	private JCheckBox whole_C_CheckBox;
     
    	public CheckBox(JTextField whole_C_QTextField, JTextField whole_C_WTextField, JTextField whole_C_PTextField) {
     
    		this.q = whole_C_QTextField;
    		this.w = whole_C_WTextField;
    		this.p = whole_C_PTextField;
     
     
    	}
    	@Override
    	public void itemStateChanged(ItemEvent e) {
     
    		if(whole_C_CheckBox.isSelected()){
     
    			q.setText("");
    			w.setText("");
    			p.setText("");
     
    		}
    	       else{
     
    			q.setText("0");
    			w.setText("0.00");
    			p.setText("0.00");
    		}	
     
     
    }}

    will when I try to run the program its working.However, when I click on the Check Box for (whole_C_CheckBox ) it give an error I don't know what is wrong with my code.

    Note: in the main class all these whole_C_QTextField, whole_C_WTextField, whole_C_PTextField has
    been set in default to (0, 0.00, 0.00), so I'm trying when I click on Check Box for (whole_C_CheckBox )
    it will set them to nothing, and if I unchecked them again they will return to their default (0, 0.00, 0.00).


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Problem with ItemListener.... help pleas

    it give an error
    Please copy the full text of the error message and paste it here. It has important info about the error.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Problem with ItemListener.... help pleas

    What error does it give you? Can you post an SSCCE that demonstrates the problem?
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  4. #4
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    Default Re: Problem with ItemListener.... help pleas

    Quote Originally Posted by Dragon3002 View Post
    public class CheckBox implements ItemListener{
     
    	private JCheckBox whole_C_CheckBox;
     
    	public CheckBox(JTextField whole_C_QTextField, JTextField whole_C_WTextField, JTextField whole_C_PTextField) {
     
    		this.q = whole_C_QTextField;
    		this.w = whole_C_WTextField;
    		this.p = whole_C_PTextField;
     
     
    	}
    }
    One thing is sure: the whole_C_CheckBox instance variable is not initialized.
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  5. #5
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    Default Re: Problem with ItemListener.... help pleas

    This is the error I get:

     
    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    	at test1.CheckBox.itemStateChanged(CheckBox.java:31)
    	at javax.swing.AbstractButton.fireItemStateChanged(Unknown Source)
    	at javax.swing.AbstractButton$Handler.itemStateChanged(Unknown Source)
    	at javax.swing.DefaultButtonModel.fireItemStateChanged(Unknown Source)
    	at javax.swing.JToggleButton$ToggleButtonModel.setSelected(Unknown Source)
    	at javax.swing.JToggleButton$ToggleButtonModel.setPressed(Unknown Source)
    	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    	at java.awt.Component.processMouseEvent(Unknown Source)
    	at javax.swing.JComponent.processMouseEvent(Unknown Source)
    	at java.awt.Component.processEvent(Unknown Source)
    	at java.awt.Container.processEvent(Unknown Source)
    	at java.awt.Component.dispatchEventImpl(Unknown Source)
    	at java.awt.Container.dispatchEventImpl(Unknown Source)
    	at java.awt.Component.dispatchEvent(Unknown Source)
    	at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    	at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    	at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    	at java.awt.Container.dispatchEventImpl(Unknown Source)
    	at java.awt.Window.dispatchEventImpl(Unknown Source)
    	at java.awt.Component.dispatchEvent(Unknown Source)
    	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    	at java.awt.EventQueue.access$200(Unknown Source)
    	at java.awt.EventQueue$3.run(Unknown Source)
    	at java.awt.EventQueue$3.run(Unknown Source)
    	at java.security.AccessController.doPrivileged(Native Method)
    	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    	at java.awt.EventQueue$4.run(Unknown Source)
    	at java.awt.EventQueue$4.run(Unknown Source)
    	at java.security.AccessController.doPrivileged(Native Method)
    	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    	at java.awt.EventQueue.dispatchEvent(Unknown Source)
    	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    	at java.awt.EventDispatchThread.run(Unknown Source)

    I looked at line 31, but I can not find what is wrong.

    Note: this is the line 31: if(whole_C_CheckBox.isSelected()){...etc

  6. #6
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    Default Re: Problem with ItemListener.... help pleas

    Quote Originally Posted by Dragon3002 View Post
    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    	at test1.CheckBox.itemStateChanged(CheckBox.java:31)

    I looked at line 31, but I can not find what is wrong.

    Note: this is the line 31: if(whole_C_CheckBox.isSelected()){...etc
    Quote Originally Posted by andbin View Post
    One thing is sure: the whole_C_CheckBox instance variable is not initialized.
    Excuse me, but isn't this clear? You have a whole_C_CheckBox that you use in itemStateChanged but that you don't inizialize.

    You have (at least) 2 options:
    1) Pass the JCheckBox reference to the CheckBox constructor and store it in whole_C_CheckBox instance variable.
    2) Use the JCheckBox reference from the ItemEvent object (since the event comes from JCheckBox the e.getSource() clearly gives that JCheckBox!)
    Andrea, www.andbin.net SCJP 5 (91%) SCWCD 5 (94%)

    Useful links for Java beginners My new project Java Examples on Google Code

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