Project Structure

• Animals3.dpr
• AnimF.pas
• Anim.pas
• AnimF.dfm

program Animals3;

uses
  Forms,
  AnimF in 'AnimF.pas' {FormAnimals},
  Anim in 'Anim.pas';

{$R *.RES}

begin
  Application.Initialize;
  Application.CreateForm(TFormAnimals, FormAnimals);
  Application.Run;
end.

unit AnimF;

interface

uses
  SysUtils, Windows, Messages, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls, Anim;

type
  TFormAnimals = class(TForm)
    LabelVoice: TLabel;
    BtnVoice: TButton;
    RbtnAnimal: TRadioButton;
    RbtnDog: TRadioButton;
    RbtnCat: TRadioButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure BtnVoiceClick(Sender: TObject);
    procedure RbtnAnimalClick(Sender: TObject);
    procedure RbtnDogClick(Sender: TObject);
    procedure RbtnCatClick(Sender: TObject);
  private
    MyAnimal: TAnimal;
  public
    { Public declarations }
  end;

var
  FormAnimals: TFormAnimals;

implementation

{$R *.DFM}

procedure TFormAnimals.FormCreate(Sender: TObject);
begin
  MyAnimal := TDog.Create;
end;

procedure TFormAnimals.FormDestroy(Sender: TObject);
begin
  MyAnimal.Free;
end;

procedure TFormAnimals.BtnVoiceClick(Sender: TObject);
begin
  LabelVoice.Caption := MyAnimal.Voice;
end;

procedure TFormAnimals.RbtnAnimalClick(Sender: TObject);
begin
  MyAnimal.Free;
  MyAnimal := TAnimal.Create;
end;

procedure TFormAnimals.RbtnDogClick(Sender: TObject);
begin
  MyAnimal.Free;
  MyAnimal := TDog.Create;
end;

procedure TFormAnimals.RbtnCatClick(Sender: TObject);
begin
  MyAnimal.Free;
  MyAnimal := TCat.Create;
end;

end.

unit Anim;

interface

type
  TAnimal = class
  public
    constructor Create;
    function GetKind: string;
    function Voice: string; virtual; abstract;
  private
    Kind: string;
  end;

  TDog = class (TAnimal)
  public
    constructor Create;
    function Voice: string; override;
    function Eat: string; virtual;
  end;

  TCat = class (TAnimal)
  public
    constructor Create;
    function Voice: string; override;
    function Eat: string; virtual;
  end;

implementation

uses
  MMSystem;

constructor TAnimal.Create;
begin
  Kind := 'An animal';
end;

function TAnimal.GetKind: string;
begin
  GetKind := Kind;
end;

constructor TDog.Create;
begin
  Kind := 'A dog';
end;

function TDog.Voice: string;
begin
  Voice := 'Arf Arf';
  PlaySound ('dog.wav', 0, snd_Async);
end;

function TDog.Eat: string;
begin
  Eat := 'A bone, please!';
end;

constructor TCat.Create;
begin
  Kind := 'A cat';
end;

function TCat.Voice: string;
begin
  Voice := 'Mieow';
  PlaySound ('cat.wav', 0, snd_Async);
end;

function TCat.Eat: string;
begin
  Eat := 'A mouse, please!';
end;

end.

object FormAnimals: TFormAnimals
  Left = 208
  Top = 106
  Width = 278
  Height = 233
  ActiveControl = BtnVoice
  Caption = 'Animals'
  Color = clBtnFace
  Font.Charset = ANSI_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = True
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  PixelsPerInch = 96
  TextHeight = 13
  object LabelVoice: TLabel
    Left = 39
    Top = 168
    Width = 201
    Height = 17
    Alignment = taCenter
    AutoSize = False
    Caption = 'Voice'
    Font.Charset = ANSI_CHARSET
    Font.Color = clBlack
    Font.Height = -16
    Font.Name = 'Arial'
    Font.Style = [fsBold]
    ParentFont = False
  end
  object BtnVoice: TButton
    Left = 152
    Top = 56
    Width = 89
    Height = 33
    Caption = '&Voice'
    TabOrder = 0
    OnClick = BtnVoiceClick
  end
  object RbtnAnimal: TRadioButton
    Left = 24
    Top = 40
    Width = 113
    Height = 41
    Caption = '&Animal'
    TabOrder = 1
    OnClick = RbtnAnimalClick
  end
  object RbtnDog: TRadioButton
    Left = 24
    Top = 72
    Width = 113
    Height = 41
    Caption = '&Dog'
    Checked = True
    TabOrder = 2
    TabStop = True
    OnClick = RbtnDogClick
  end
  object RbtnCat: TRadioButton
    Left = 24
    Top = 104
    Width = 113
    Height = 41
    Caption = '&Cat'
    TabOrder = 3
    OnClick = RbtnCatClick
  end
end