How to set a third state in a JCheckBox

Question

Hello
Does someone know how can I set a third state (for example if the value is null instead of true or false) on a JCheckBox.
The goal is that I can set this state myself with a click on the checkbox, so the method setEnabled(false) doesn't work.
Thanks

Answer 1

How about tinkering with the "enabled" property?
That is, a 3-state check box is a check box that
the user can disable/enable by clicking on it.
I changed the code, assuming that the UI asks the
model if the control is enabled. It apparently works
(I'm using 1.3)
Any comments?
import java.awt.*;
import javax.swing.*;
// A Three State JCheckBox which takes an int via getSelected/setSelected methods
// The null state is drawn as "disabled"
// after http://forum.java.sun.com/thread.jsp?forum=57&thread=124056
public class ThreeCheckBox extends JCheckBox
     ThreeToggleButtonModel theModel = new ThreeToggleButtonModel();
     public ThreeCheckBox(String aString)
          this(aString, 2);
     public ThreeCheckBox(String aString, int v)
          super(aString);
          theModel.setSelected(v);
          setModel(theModel);
     public void paintComponent(Graphics g)
          theModel.beforePaint();          
          super.paintComponent(g);
          theModel.afterPaint();          
     public int getSelected() { return theModel.getSelected(); }
     public void setSelected(int v)
          theModel.setSelected(v);
     class ThreeToggleButtonModel extends JToggleButton.ToggleButtonModel
          private boolean isPaint = false;
          private int theValue = 2;
          public int getSelected() { return theValue; }
          public boolean isEnabled()
               return isPaint && theValue > 1 ? false : super.isEnabled();
          public void beforePaint() { isPaint = true; }
          public void afterPaint() { isPaint = false; }
          public void setSelected(int v)
               theValue = v < 0 ? 2 : v;
               super.setSelected(v == 1);
          public void setSelected(boolean b)
               theValue = (theValue + 1) % 3;
               super.setSelected(theValue == 1);