Understand the Delphi Class (V)

To create a new VCL Forms application project, two classes already appear in the code:

One is the Tform class; One is the TForm1 class; TForm1 inherited from Tform.

Tform is the parent class of TForm1; TForm1 is a subclass of Tform.

unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, StdCtrls;
type
　TForm1 = class(TForm)
　　Button1: TButton;
　　Button2: TButton;
　　procedure Button1Click(Sender: TObject);
　　procedure Button2Click(Sender: TObject);
　end;
The following custom two classes, Tchild inherited from Tbass
　TBass = class
　　procedure msg1;
　end;
　TChild = class(TBass)
　　procedure msg2;
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
{ TBass }
procedure TBass.msg1;
begin
　ShowMessage('is Bass');
end;
{ TChild }
procedure TChild.msg2;
begin
　ShowMessage('is Child');
end;
Test 1: The parent class has only one method Msg1
procedure TForm1.Button1Click(Sender: TObject);
var
　b: TBass;
begin
　b := TBass.Create;
　b.msg1; {is Bass}
　b.Free;
end;
Test 2: Subclass has two methods, one MSG2, and inherits a MSG1
procedure TForm1.Button2Click(Sender: TObject);
var
　c: TChild;
begin
　c := TChild.Create;
　c.msg1; {is Bass}
　c.msg2; {is Child}
　c.Free;
end;
end.