public Object getValueAt(int row, int col) {
            Object result = null;
            if(col==0)
                result =  parts[row].getGateClass().getName();
            else if (col==1) {
                if (parts[row] instanceof CompositeGate)
                    result = COMPOSITE_GATE;
                else if (parts[row] instanceof BuiltInGate)
                    result = BUILTIN_GATE;
            }
            else if (col==2)
                result = new Boolean(parts[row].getGateClass().isClocked());
            return result;
        }