Problem with ItemListener.... help pleas

**Dragon3002** · February 24th, 2014, 07:48 AM

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).

**Norm** · February 24th, 2014, 08:32 AM

it give an error

Please copy the full text of the error message and paste it here. It has important info about the error.

**KevinWorkman** · February 24th, 2014, 08:34 AM

What error does it give you? Can you post an SSCCE that demonstrates the problem?

**andbin** · February 24th, 2014, 08:38 AM

Originally Posted by Dragon3002

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.

**Dragon3002** · February 26th, 2014, 05:11 AM

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

**andbin** · February 26th, 2014, 06:21 AM

Originally Posted by Dragon3002

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

Originally Posted by andbin

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!)

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