Why use property in a class?

Question

I was just wondering about why should I use property in a class instead of \"normal\" variables (class attributes?). What I mean is this:

TSampleClass = clas         


        

Answer 1

I know that I can define getter and setter methods for getting or saving the property respectively, but that is possible even without the variable being a "property".

Well, no. Setters and getters are just normal methods that are called as such only once they are used as the read and write members of a property. Not having a property means not having a getter or a setter, even if they are named as such. Furthermore; setters and getters are typically declared private or protected. So being able to call them when you use a public field instead of using a public property would require to move those methods to the public section.

Also, a big difference between fields and properties is the ability to be published and thus can be used in the object inspector. Fields (of other types then class or interface) can not be declared as published.

Properties can also be of great importance - or be usefull - in inheritance. Technically, you can't override a property, but you can mimic override in several ways. Some examples where property Name can be called from TDescendant, each with its own purpose:

1) Abstraction:

TBase = class(TObject)
protected
  function GetName: String; virtual; abstract;
  procedure SetName(const Value: String); virtual; abstract;
public
  property Name: String read GetName write SetName;
end;

TDescendant = class(TBase)
private
  FName: String;
protected
  function GetName: String; override;
  procedure SetName(const Value: String); override;
end;

2a) Protection (like Krom mentioned, ):

TBase = class(TObject)
private
  FName: String;
  function GetName: String;
  procedure SetName(const Value: String);
protected
  property Name: String read GetName write SetName;
end;

TDescendant = class(TBase)
public
  property Name;
end;

2b)

TBase = class(TObject)
private
  FName: String;
protected
  function GetName: String;
  procedure SetName(const Value: String);
end;

TDescendant = class(TBase)
public
  property Name: String read GetName write SetName;
end;

By combinination of the above, you could change the behaviour of properties for descendant classes.