if ( constraint==null ) { center = c; return; }
if (constraint == null) constraint = CENTER;
    public void addComponent(SComponent c, Object constraint) {        if ( constraint==null ) {            center = c;            return;        }        if ( constraint.equals(NORTH) )            north = c;        else if ( constraint.equals(SOUTH) )            south = c;        else if ( constraint.equals(EAST) )            east = c;        else if ( constraint.equals(WEST) )            west = c;        else            center = c;    }