请高手帮忙---如何在多态下的一个子类中再写一个子类 ( 积分: 50 )

你已经写的差不多了，接着继续～
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TForm1 = class(TForm)
btn1: TButton;
btn2: TButton;
btn3: TButton;
btn4: TButton;
btn5: TButton;
btn6: TButton;
btn7: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure Button3Click(Sender: TObject);
procedure Button4Click(Sender: TObject);
procedure Button5Click(Sender: TObject);
procedure Button6Click(Sender: TObject);
procedure btn7Click(Sender: TObject);

private
{ Private declarations }
public
{ Public declarations }
end;

TTransform=class
public
procedure ChooseTransform;
virtual;
abstract;
end;

TPlane=class(TTransform)
public
procedure ChooseTransform;override;
end;

TBoat=class(TTransform)
public
procedure ChooseTransform;override;
end;

TCar=class(TTransform)
public
procedure ChooseTransform;override;
end;

TTrain=Class(TTransform)
public
procedure ChooseTransform;override;
end;

TSpaceShip=class(TTransform)
public
procedure ChooseTransform;
override;
end;

TBike=class(TTransform)
public
procedure ChooseTransform;
override;
end;

TRedBike = class(TBike)
public
procedure ChooseTransform;
override;
end;

var
Form1: TForm1;
implementation
{$R *.dfm}
{ TPlane }
procedure TPlane.ChooseTransform;
begin
inherited;
//飞机
ShowMessage('您已经选择了飞机');
end;

{ TBoat }
procedure TBoat.ChooseTransform;
begin
inherited;
// 船
ShowMessage('您已经选择了船');
end;

{ TCar }
procedure TCar.ChooseTransform;
begin
inherited;
//汽车
ShowMessage('您已经选择了汽车');
end;

{ TTrain }
procedure TTrain.ChooseTransform;
begin
inherited;
//火车
ShowMessage('您已经选择了火车');
end;

{ TSpaceShip }
procedure TSpaceShip.ChooseTransform;
begin
inherited;
//宇宙飞船
ShowMessage('您已经选择了宇宙飞船');
end;

{ TBike }
procedure TBike.ChooseTransform;
begin
inherited;
//自行车
ShowMessage('您已经选择了自行车');
end;

procedure TForm1.Button1Click(Sender: TObject);
var
a:TTransform;
begin
a:=TPlane.Create;
a.ChooseTransform;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
b:TTransform;
begin
b:=TCar.Create;
b.ChooseTransform;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
c:TTransform;
begin
c:=TTrain.Create;
c.ChooseTransform;
end;

procedure TForm1.Button4Click(Sender: TObject);
var
d:TTransform;
begin
d:=TBoat.Create;
d.ChooseTransform;
end;

procedure TForm1.Button5Click(Sender: TObject);
var
e:TTransform;
begin
e:=TSpaceShip.Create;
e.ChooseTransform;
end;

procedure TForm1.Button6Click(Sender: TObject);
var
f:TTransform;
begin
f:=TBike.Create;
f.ChooseTransform;
end;

{ TRedBike }
procedure TRedBike.ChooseTransform;
begin
inherited;
ShowMessage('您已经选择了自行车-Red');
end;

procedure TForm1.btn7Click(Sender: TObject);
var
f:TTransform;
begin
f:=TRedBike.Create;
f.ChooseTransform;
end;

end.

接受答案了.