unit Tpl_meth;
{
Design pattern example -
some simple classes using the Template Method pattern.
}
interface
type
TAbstractTemplateClass = class(TObject)
protected
function Algorithm_StepA: Integer; virtual; abstract;
function Algorithm_StepB: Integer; virtual; abstract;
function Algorithm_StepC: Integer; virtual; abstract;
public
function Algorithm: Integer;
end;
TConcreteClassA = class(TAbstractTemplateClass)
protected
function Algorithm_StepA: Integer; override;
function Algorithm_StepB: Integer; override;
function Algorithm_StepC: Integer; override;
end;
TConcreteClassB = class(TAbstractTemplateClass)
protected
function Algorithm_StepA: Integer; override;
function Algorithm_StepB: Integer; override;
function Algorithm_StepC: Integer; override;
end;
implementation
function TAbstractTemplateClass.Algorithm: Integer;
begin
Result := Algorithm_StepA +
Algorithm_StepB +
Algorithm_StepC;
end;
function TConcreteClassA.Algorithm_StepA: Integer;
begin
Result := 1;
end;
function TConcreteClassA.Algorithm_StepB: Integer;
begin
Result := 2;
end;
function TConcreteClassA.Algorithm_StepC: Integer;
begin
Result := 3;
end;
function TConcreteClassB.Algorithm_StepA: Integer;
begin
Result := 4;
end;
function TConcreteClassB.Algorithm_StepB: Integer;
begin
Result := 5;
end;
function TConcreteClassB.Algorithm_StepC: Integer;
begin
Result := 6;
end;
end.
/////////////////////////////////////////////////////////////////////////////////
unit Unit1;
interface
uses
SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
Forms, Dialogs, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
uses tpl_meth;
procedure TForm1.Button1Click(Sender: TObject);
var
AnAbstractObject: TAbstractTemplateClass;
begin
AnAbstractObject := TConcreteClassA.Create;
try
ShowMessage('Algorithm Result = ' + Inttostr(AnAbstractObject.Algorithm));
finally
AnAbstractObject.Destroy;
end;
end;
procedure TForm1.Button2Click(Sender: TObject);
var
AnAbstractObject: TAbstractTemplateClass;
begin
AnAbstractObject := TConcreteClassB.Create;
try
ShowMessage('Algorithm Result = ' + Inttostr(AnAbstractObject.Algorithm));
finally
AnAbstractObject.Destroy;
end;
end;
end.
