unit Unit1;
interface
uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls;
type
   //定义接口如果接口独立成一个文件，则在应用程序中和实现程序中都要引用该接口文件；
    ICar = interface (IInterface)
        ['{ED52E264-6683-11D7-B847-001060806215}']
        procedure drive;
    end;
 
//接口实现类1，一定要加入TinterfacedObject才能使用；
    TCar = class(TInterfacedObject,ICar)
    public
        procedure drive;
    end;
//接口实现类2，一定要加入TinterfacedObject才能使用；
    THouseCar = class(TInterfacedObject,ICar)
    public
        procedure drive;
    end;
 
 TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
 private
    { Private declarations }
 public
    { Public declarations }
    function getCar:ICar; //此处可用别的方式来实现获取ICAR，如放在DLL文件中；
 end;
 
var
 Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
{ TCar }
procedure TCar.drive;
begin
 ShowMessage('TCar.drive');
end;
 
{ THouseCar }
procedure THouseCar.drive;
begin
   ShowMessage('THouseCar.drive');
end;
 
procedure TForm1.Button1Click(Sender: TObject);
var
 s:ICar;
begin
 s:= getCar;
 s.drive;
end;
 
function TForm1.getCar:ICar;
begin
   Result:=THouseCar.Create; //此处为整个实现的关键点；
//或Result:=TCar.Create;
end;
 
end.