How to unselect and undo with checkboxes using Java Swing?

I have a checkbox, when the checkbox is selected I want to add int 2 to my total. Then I want to be able to unselect it and then subtract int 2 to my total.

At the moment, I cant unselect and subtract 2.

Also, my checkbox is in a button group so I need to use clearSelection() as a solution to deselect.

The code I currently have for this is (which isn't work too well):

monTill4ChckBox.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {

            if(monTill4ChckBox.isSelected()){

                mondayCost= mondayCost + 2; 
            }
            else{
            mondayCost= mondayCost - 2;             
            monAftergroup.clearSelection();
            }