关于多态的理解，有助于理解TStream抽象类的多态机制。

unit Unit11;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm11 = class(TForm)
    btn1: TButton;
    btn2: TButton;
    procedure btn1Click(Sender: TObject);
    procedure btn2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

  TFuLei = class
    public
      function func1(): string; virtual;
  end;

  TZiLei = class(TFuLei)
    public
      function func1(): string; override;
  end;

var
  Form11: TForm11;

implementation

{$R *.dfm}

function TFuLei.func1(): string;
begin
  Exit(‘func1‘);
end;

function TZiLei.func1(): string;
begin
  Exit(‘func2‘);
end;

/// <summary>
/// 注意这里的参数是父类,意思是如果传入子类也是可以的,因为子类拥有父类所有的功能,可以向上递归
/// 且如果子类的覆盖度了父类的方法,那么传入子类的话,delphi会自动调用子类覆盖后的方法
/// </summary>
procedure wokao(ALei: TFuLei);
begin
  ShowMessage(ALei.func1);
end;

procedure TForm11.btn1Click(Sender: TObject);
var
  lei: TFuLei;
begin
  lei := TFuLei.Create;
  wokao(lei);//func1
  lei.Free;
end;

procedure TForm11.btn2Click(Sender: TObject);
var
  lei: TZiLei;
begin
  lei := TZiLei.Create;
  wokao(lei);//func2
  lei.Free;
end;

end.