private String getImageClass() {

        switch (m_state) {
            case on:
                return CSS.triStateOn();
            case off:
                return CSS.triStateOff();
            case middle:
            default:
                return CSS.triStateMedium();
        }

    }
private String getImageClass ( ) { switch ( m_state ) { case on : return CSS . triStateOn ( ) ; case off : return CSS . triStateOff ( ) ; case middle : default : return CSS . triStateMedium ( ) ; } }
Gets the image class to use for the check box.<p>

@return the image class