FULL PRODUCT VERSION :
Java 1.5.0
Java 1.4.2_05

ADDITIONAL OS VERSION INFORMATION :
Windows XP 5.1.2600
Mac OS X

A DESCRIPTION OF THE PROBLEM :
If you create a JSlider using the constructor that takes a BoundedRangeModel and then add a ChangeListener to the slider, then programmatically setting the value of the slider will result in the ChangeListener being called twice. I have located the problematic code.

The code for the JSlider constructor that takes a BoundedRangeModel is:

    public JSlider(BoundedRangeModel brm)
    {
        this.orientation = JSlider.HORIZONTAL;
        setModel(brm);
        sliderModel.addChangeListener(changeListener);
        updateUI();
    }

Note that after adding an internal ChangeListener you call setModel(). The problem is that setModel itself adds a ChangeListener. This results in a double call to the user's ChangeListener when programmatically setting the value of the JSlider.

Fortunately there is an easy workatound in this case. Rather than calling the constructor that takes a BoundedRangeModel, call the one that takes a min, max and value. Here is the code for that constructor:

    public JSlider(int orientation, int min, int max, int value)
    {
        checkOrientation(orientation);
        this.orientation = orientation;
        sliderModel = new DefaultBoundedRangeModel(value, 0, min, max);
        sliderModel.addChangeListener(changeListener);
        updateUI();
    }

Note that rather than calling setModel(), this code just assigns a new BoundedRangeModel to the sliderModel variable directly. You don't end up with two change listeners installed.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Just create a JSlider using the constructor that takes a BoundedRangeModel. Then add a ChangeListener to the slider. Then programattically set the slider's value.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
When the sliders's value is programmatically set, my ChangeListener should be called once.
ACTUAL -
The ChangeListener is called twice in succession.

REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
If you can call the constructor that takes min, max and value, the bug will not happen.
###@###.### 2005-06-01 10:51:03 GMT