unit IntfUnit;

interface

uses
  Classes, SysUtils, Dialogs;

type
  IFormattedNumber = interface
    ['{2DE825C1-EADF-11D2-B39F-0040F67455FE}']
    function FormattedString: string;
    function GetName: string;
  end;

  TFormattedInteger = class(TInterfacedObject, IFormattedNumber)
  private
    FValue: Integer;
  public
    constructor Create(AValue: Integer);
    destructor Destroy; override;
    function FormattedString: string;
    function GetName: string;
  end;

  TFormattedHexInteger = class(TFormattedInteger, IFormattedNumber)
  public
    destructor Destroy; override;
    function FormattedString: string;
    function GetName: string;
  end;

implementation

uses
  MainForm;

{ TFormattedInteger }

constructor TFormattedInteger.Create(AValue: Integer);
begin
  inherited Create;

  FValue := AValue;
end;

destructor TFormattedInteger.Destroy;
begin
  Form1.Memo1.Lines.Add('TFormattedInteger.Destroy');

  inherited Destroy;
end;

function TFormattedInteger.FormattedString: string;
begin
  Result := 'The integer is ' + IntToStr(FValue);
end;

function TFormattedInteger.GetName: string;
begin
  Result := 'TFormattedInteger.GetName';
end;

{ TFormattedHexInteger }

destructor TFormattedHexInteger.Destroy;
begin
  Form1.Memo1.Lines.Add('TFormattedHexInteger.Destroy');

  inherited Destroy;
end;

function TFormattedHexInteger.FormattedString: string;
begin
  Result := 'The hex integer is $' + IntToHex(FValue, 4);
end;

function TFormattedHexInteger.GetName: string;
begin
  Result := 'TFormattedHexInteger.GetName';
end;

end.