Entry
Delphi: Class: Inheritance: Create: Simple: Can you give an example of inheritance?
Jan 10th, 2004 16:00
Knud van Eeden,
----------------------------------------------------------------------
--- Knud van Eeden --- 27 September 2003 - 06:59 pm ------------------
Delphi: Class: Inheritance: Create: Simple: Can you give an example of
inheritance?
1. In general:
---
Steps: Overview:
---
1. -Create a class <yourclassnameparent>:
http://www.faqts.com/knowledge_base/view.phtml/aid/24789/fid/175
---
2. -Create another class <yourclassnamechild>:
1. To indicate that you want to use inheritance, use the following
notation:
<yourclassnamechild> = class ( <yourclassnameparent> )
// do something
// e.g. -add new variables, functions and procedures
//
// and or
//
// -overwrite existing variables, functions
// and procedures of that 'parent' class
end;
2. So you indicate that your class is inheriting, by writing:
1. first the name of the 'child' class
2. followed by the equal sign '='
3. followed by the word 'class'
4. followed by an open parenthesis '('
5. followed by the name of the 'parent' class
6. followed by a closed parenthesis ')'
---
---
2. In specific:
---
1. -Create a parent class 'addressC':
addressC = class
//
private
//
nameS : string;
streetS : string;
cityS : string;
countryS : string;
telephoneS : string;
emailS : string;
//
procedure PROCView;
//
// constructor for parent class
constructor Create( nameS : string; streetS : string; cityS :
string; countryS : string; telephoneS : string; emailS : string );
//
destructor Destroy;
end;
---
2. -Create another child class 'addresscompanyC':
addresscompanyC = class ( addressC )
//
private
//
companynameS : string;
//
procedure PROCView;
//
constructor Create( nameS : string; streetS : string; cityS :
string; countryS : string; telephoneS : string; emailS : string;
companynameS : string );
//
destructor Destroy;
end;
---
3. -Then give the code for the procedures or functions used in that
class:
1. For the parent class:
procedure addressC.PROCView;
begin
ShowMessage( nameS + ' ' + '-' + ' ' + streetS + ' ' + '-'
+ ' ' + cityS + ' ' + '-' + ' ' + countryS + ' ' + '-' + ' ' +
telephoneS + ' ' + '-' + ' ' + emailS );
end;
constructor addressC.Create( nameS : string; streetS :
string; cityS : string; countryS : string; telephoneS : string;
emailS : string );
begin
self.nameS := nameS;
self.streetS := streetS;
self.cityS := cityS;
self.countryS := countryS;
self.telephoneS := telephoneS;
self.emailS := emailS;
end;
---
See also:
http://www.faqts.com/knowledge_base/view.phtml/aid/16108/fid/175
---
destructor addressC.Destroy;
begin
end;
---
2. For the child class:
procedure addresscompanyC.PROCView;
begin
ShowMessage( nameS + ' ' + '-' + ' ' + streetS + ' ' + '-'
+ ' ' + cityS + ' ' + '-' + ' ' + countryS + ' ' + '-' + ' ' +
telephoneS + ' ' + '-' + ' ' + emailS + ' ' + '-' + ' ' +
companynameS );
end;
constructor addresscompanyC.Create( nameS : string; streetS :
string; cityS : string; countryS : string; telephoneS : string;
emailS : string; companynameS : string );
begin
inherited Create( nameS, streetS, cityS, countryS,
telephoneS, emailS ); // call the constructor of the parent class
self.companynameS := companynameS;
end;
destructor addresscompanyC.Destroy;
begin
inherited Destroy;
end;
---
4. -Declare the variables which you intend to use with your class:
var
knudO : addressC;
vanessaO : addressC;
knudcompanyO : addresscompanyC;
vanessacompanyO : addresscompanyC;
---
5. -Supply some source code where you use your class:
1. Put a button on the form
2. Double click on it
3. Type the following source code text:
procedure TForm1.Button1Click(Sender: TObject);
// create
var knudO : addressC;
var vanessaO : addressC;
var knudcompanyO : addresscompanyC;
var vanessacompanyO : addresscompanyC;
begin
// initialize using constructor
knudO := addressC.Create( 'myname', 'mystreet
1', 'mycity', 'mycountry', '01-2345678', 'myemail@address' );
vanessaO := addressC.Create( 'anothername', 'anotherstreet
1', 'anothercity', 'anothercountry', '01-
3456789', 'anotheremail@address' );
knudcompanyO := addresscompanyC.Create( 'myname', 'mystreet
1', 'mycity', 'mycountry', '01-
2345678', 'myemail@address', 'thecompany1name' );
vanessacompanyO := addresscompanyC.Create
( 'anothername', 'anotherstreet
1', 'anothercity', 'anothercountry', '01-
3456789', 'anotheremail@address', 'thecompany2name' );
// do something
knudO.PROCView;
knudcompanyO.PROCView;
// remove using destructor
knudO.Free;
vanessaO.Free;
knudcompanyO.Free;
vanessacompanyO.Free;
end;
---
6. -This gives alltogether the following source code:
--- cut here ---------------------------------------------------------
// save e.g. as 'unit1.pas' in directory 'testinheritance'.
// and save the project e.g. as 'testinheritance.dpr'
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics,
Controls, Forms,
Dialogs, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
// --- 1. declaration of the 'parent' class --- //
addressC = class
//
// it can be 'private', because
// classes have access to each others
// private and protected variables,
// if they are put in the same unit file
// (as is the case here) in Delphi.
//
private
//
nameS : string;
streetS : string;
cityS : string;
countryS : string;
telephoneS : string;
emailS : string;
//
// 1.1.1 a getter for the 'parent' class
procedure PROCView;
//
//
// 1.1.2 the 'constructor' for the 'parent' class
constructor Create( nameS : string; streetS : string; cityS :
string; countryS : string; telephoneS : string; emailS : string );
//
//
// 1.1.3 the 'destructor' for the 'parent' class
destructor Destroy;
end;
// --- 2. declaration of the 'child' class --- //
addresscompanyC = class ( addressC )
//
private
//
companynameS : string;
//
//
// 2.1.1 a 'getter' for the 'child' class
procedure PROCView;
//
//
// 2.1.2 the 'constructor' for the 'child' class
constructor Create( nameS : string; streetS : string; cityS :
string; countryS : string; telephoneS : string; emailS : string;
companynameS : string );
//
//
// 2.1.3 the 'destructor' for the 'child' class
destructor Destroy;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
// --- 1.1 functions and procedures of the 'parent' class --- //
// 1.1.1 a 'getter' of the 'parent' class
procedure addressC.PROCView;
begin
ShowMessage( nameS + ' ' + '-' + ' ' + streetS + ' ' + '-'
+ ' ' + cityS + ' ' + '-' + ' ' + countryS + ' ' + '-' + ' ' +
telephoneS + ' ' + '-' + ' ' + emailS );
end;
// 1.1.2 the 'constructor' of the 'parent' class
constructor addressC.Create( nameS : string; streetS : string;
cityS : string; countryS : string; telephoneS : string; emailS :
string );
begin
self.nameS := nameS;
self.streetS := streetS;
self.cityS := cityS;
self.countryS := countryS;
self.telephoneS := telephoneS;
self.emailS := emailS;
end;
// 1.1.3 the 'destructor' of the 'parent' class
destructor addressC.Destroy;
begin
inherited Destroy;
end;
// --- 2.1 functions and procedures of the 'child' class --- //
// 2.1.1 a 'getter' of the 'child' class
procedure addresscompanyC.PROCView;
begin
ShowMessage( nameS + ' ' + '-' + ' ' + streetS + ' ' + '-'
+ ' ' + cityS + ' ' + '-' + ' ' + countryS + ' ' + '-' + ' ' +
telephoneS + ' ' + '-' + ' ' + emailS + ' ' + '-' + ' ' +
companynameS );
end;
// 2.1.2 the 'constructor' for the 'child' class (which calls
the 'constructor' of the 'parent' class first)
constructor addresscompanyC.Create( nameS : string; streetS :
string; cityS : string; countryS : string; telephoneS : string;
emailS : string; companynameS : string );
begin
inherited Create( nameS, streetS, cityS, countryS, telephoneS,
emailS ); // call the constructor of the parent class
self.companynameS := companynameS;
end;
// 2.1.3 the 'destructor' of the 'child' class
destructor addresscompanyC.Destroy;
begin
inherited Destroy;
end;
// --- 3. do something --- //
procedure TForm1.Button1Click(Sender: TObject);
//
// 3.1.1 create variables representing that 'parent' class:
//
var knudO : addressC;
var vanessaO : addressC;
//
// 3.2.1 create variables representing that 'child' class:
//
var knudcompanyO : addresscompanyC;
var vanessacompanyO : addresscompanyC;
begin
//
// 3.1.2 initialize variables representing that 'parent' class:
//
knudO := addressC.Create
( 'myname', 'mystreet', 'mycity', 'mycountry', '01-
2345678', 'myemail@address' );
vanessaO := addressC.Create( 'anothername', 'anotherstreet
1', 'anothercity', 'anothercountry', '01-
3456789', 'anotheremail@address' );
//
// 3.2.2 initialize variables representing that 'child' class:
//
knudcompanyO := addresscompanyC.Create( 'myname', 'mystreet
1', 'mycity', 'mycountry', '01-
2345678', 'myemail@address', 'thecompany1name' );
vanessacompanyO := addresscompanyC.Create
( 'anothername', 'anotherstreet
1', 'anothercity', 'anothercountry', '01-
3456789', 'anotheremail@address', 'thecompany2name' );
//
// 3.3 do something
//
// 3.3.1 view variables stored in the variables representing
that 'parent' class:
//
knudO.PROCView;
vanessaO.PROCView;
//
// 3.3.2 view variables stored in the variables representing
that 'child' class:
//
knudcompanyO.PROCView;
vanessacompanyO.PROCView;
//
// 3.4.1 remove variables from 'parent' class,
using 'destructor'
//
knudO.Free;
vanessaO.Free;
//
// 3.4.2 remove variables from 'child' class, using 'destructor'
//
knudcompanyO.Free;
vanessacompanyO.Free;
end;
end.
--- cut here ---------------------------------------------------------
7. -When you run this source code, you will see a message box with
that address information:
+---------------------------------------------------------------------+
|myname - mystreet - mycity - mycountry - 01-2345678 - myemail@address|
| |
| +----+ |
| | OK | |
| +----+ |
+---------------------------------------------------------------------+
Followed by another message box:
+---------------------------------------------------------------------+
|anothername - anotherstreet 1 - anothercity - anothercountry - |
|01-3456789 - anotheremail@address |
| |
| +----+ |
| | OK | |
| +----+ |
+---------------------------------------------------------------------+
Followed by another message box:
+--------------------------------------------------------------------+
|myname - mystreet 1 - mycity - mycountry - 01-2345678 - |
|myemail@address - thecompany1name |
| |
| +----+ |
| | OK | |
| +----+ |
+--------------------------------------------------------------------+
Followed by another message box:
+---------------------------------------------------------------------+
|anothername - anotherstreet 1 - anothercity - anothercountry - |
|01-3456789 - anotheremail@address - thecompany2name |
| |
| +----+ |
| | OK | |
| +----+ |
+---------------------------------------------------------------------+
---
---
Internet: see also:
---
C#: Class: Inheritance: Create: Simple: Can you give an example of
inheritance?
http://www.faqts.com/knowledge_base/view.phtml/aid/24889/fid/791
---
C++: Class: Inheritance: Create: Simple: Can you give an example of
inheritance?
http://www.faqts.com/knowledge_base/view.phtml/aid/24882/fid/163
---
Delphi: Class: Inheritance: What is inheritance?
http://www.faqts.com/knowledge_base/view.phtml/aid/24869
---
Java: Class: Inheritance: Create: Simple: Can you give an example of
inheritance?
http://www.faqts.com/knowledge_base/view.phtml/aid/24891/fid/165
----------------------------------------------------------------------
