EVALUATION

The getClickCount() method in MouseEvent is more flexible than a double-click event would be, because it allows detection of double, triple, or any tuple click.

As the code below demonstrates, it is possible to get the behavior you expect using mouseClicked() by checking that the click count is divisible by 2:

// Test that checking for an event number of clicks in click count will
// correctly toggle a Component

import java.awt.*;
import java.awt.event.*;

public class BClickCountTest extends Frame implements MouseListener {
    public BClickCountTest () {
        addMouseListener(this);
        setSize(400, 400);
    }

    public static void main(String[] args) {
        BClickCountTest t = new BClickCountTest();
        t.show();
    }

    public void toggle() {
        if (getBackground() == Color.red) {
            setBackground(Color.green);
        } else {
            setBackground(Color.red);
        }
    }

    public void mouseClicked (MouseEvent e){
        System.out.print("clickcount = " + e.getClickCount());
        if (e.getClickCount() % 2 == 0) {
            System.out.println(", TOGGLE");
            toggle();
        } else {
            System.out.println("");
        }
    }
    public void mousePressed(MouseEvent e){}
    public void mouseReleased(MouseEvent e){}
    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}
}

When the mouse is double-(or quadruple-, or sextuple-, or octuple-, etc)clicked, the Frame's background color is toggled between red and green.  This behaves in a similar fashion to the windows Explorer, in that each even-numbered click causes a toggle.  You don't need to use mousePressed()/mouseReleased() for this.

The reason that JTree doesn't behave this way is that BasicTreeUI checks if the number of clicks in the MouseEvent is equal to the desired number of clicks, not modulo:

    protected boolean isToggleEvent(MouseEvent event) {
	if(!SwingUtilities.isLeftMouseButton(event)) {
	    return false;
	}
	int           clickCount = tree.getToggleClickCount();

	if(clickCount <= 0) {
	    return false;
	}
-->	return (event.getClickCount() == clickCount);
    }

You should be able to install your own TreeUI that uses your own isToggleEvent() which responds to every even-numbered click.  However, the Windows Look & Feel should also behave this way.  I'm going to pass this to Swing to fix that aspect.
###@###.### 2001-12-07

Interestingly Windows explorer does not exhibit the behavior that a click count % 2 is equivalent to a toggle, where as the tree in regedit does.
I've provided a workaround that will provide windows behavior.
###@###.### 2005-1-03 18:39:19 GMT

Windows doesn't appear to offer up a click count, only single and double click events.  What Java generates as a quarduple click is equivalent to two double clicks on windows.  So, tree should be using % here (at least for windows).
The change will offer a new ui property, "Tree.useEqualsForToggle", that if flase will use %.  The default is true, so that == is used.
###@###.### 2005-1-06 17:37:42 GMT

After talking with Shannon we decided to make the change for all look and feels and remove the property.
###@###.### 2005-1-06 19:22:10 GMT
                                     

WORK AROUND



Name: gm110360			Date: 12/05/2001


Use mouse pressed / released instead of mouse clicked to detect double clicks.
This works at least on Windows.
======================================================================

You can also install your own TreeUI that responds to all even-numbered clicks.
###@###.### 2001-12-07

A simpler approach is set the toggle click count to a negative number, say -1, and install a MouseListener that handles the actual toggling.  Here's a rough cut at it:

        tree.addMouseListener(new MouseAdapter() {
                public void mouseClicked(MouseEvent e) {
                    if (e.getModifiers() == InputEvent.BUTTON1_MASK &&
                              e.getClickCount() > 0 &&
                              e.getClickCount() % 2 == 0) {
                        int row = tree.getRowForLocation(e.getX(), e.getY());
                        if (row != -1) {
                            if (tree.isExpanded(row)) {
                                tree.collapseRow(row);
                            }
                            else {
                                tree.expandRow(row);
                            }
                        }
                    }
                }

            });

###@###.### 2005-1-03 18:39:19 GMT
                                     

SUGGESTED FIX

------- BasicTreeUI.java -------
*** /tmp/sccs.3eaOUs    Fri Dec  7 16:33:06 2001
--- BasicTreeUI.java    Fri Dec  7 16:33:02 2001
***************
*** 2141,2147 ****
        if(clickCount <= 0) {
            return false;
        }
!       return (event.getClickCount() == clickCount);
      }
  
      /**
--- 2141,2147 ----
        if(clickCount <= 0) {
            return false;
        }
!       return (event.getClickCount() % clickCount == 0);
      }
  
      /**