Thanks Roedy, I've read the source of JRButton and ButtonGroup, I find
that I can change the uiClassID from "JRadioButtonUI"
to "JButtonUI" to let the RadioButton look like normal JButton. But
I'm not very familiar with define my own event and listener,
like you suggest to add listener for ButtonGroup events. Can you
please brief a little more about what kind of event and event
method I may be used ?
Many thanks.

Ray

You should never try to guess the customers of a design. You assume
the software is used by public users while
it's always possible that the special user group want some feature
which may against the common
accepting standard. I suggest never try to type such question if you
don't know how to answer my technical question.

I've come up with a solution here.
define my new class:
ChangedRadioButton extends JRadioButton{

in constructor:
public ChangedRadioButton (){
  super();
  setModel(new ChangedRBModel());//force to use new ButtonModel
}

//define an inner class that extends that JToggleButtonModel used by
the JRadioButton
private class ChangedRBModel extends JToggleButtonModel{
  public void setSelected(boolean b){//try to override this method
       ....//copy code from JToggleButtonModel
        if(b)
            ChangedRadioButton.this.setBackground(colorSelected);
        else
            ChangedRadioButton.this.setBackground(colorUnselected);
  }
}

}//ends ChangedRadioButton class

This works because I guess when one radioButton of a group get
selected, rest buttons will call their ButtonModel.setSelected(false),
so the setBackground(color) line is called also.
However, if you try to add simple ActionListner or ItemListener, they
will listen to user input.
They won't get executed if another button in the group get selected
which require the previous selected button on which these Listener is
added get unselected.

The reason I don't use JToggleButton is that the toggle has two states
and associate with two appearances.
When click and selected, it's hightlighted, second click will
disselect and unhighlight. But our need is when
click it's always selected, acting like a normal button.

Ray