----- Original Message -----
From: "Paule Ecimovic" <[EMAIL PROTECTED]>
To: "Borland's Delphi Discussion List" <[email protected]>
Sent: Monday, April 24, 2006 2:08 AM
Subject: Re: Delphi and Java
> Hi, Kevin and All
>
> Your comment about using instance variables as 'pointers' raises an
> interesting question of how object oriented programming has conceptually
> replaced pointers. A transition from a pointer-intensive language like C,
> where pointers are used compulsively even if they are not necessary, to an
> object-oriented language such as C++, Delphi or more restrictively Java.
> Where have all those pointers gone ? :-) and how do object-oriented
> languages design-pattern them out of explicit code all together?
The more I have been using a heavily OO approach, the less I have been using
pointers explicitly (I practically never use the Tpointer declaration);
however Delphi instance variables
are really pointers to assigned memory (Student.Course.Coursename is a
pointer to a pointer to a pointer to a string)
The use of namespaces and structs in C# (simple variables are not declared
as 'free' variables but
part of an object structure) favour or even impose an OO approach;
(I find it more ordered and intelligible: C was famous for causing ambiguity
with its use of pointers,
I have also seen globally declared variables in Delphi cause havoc due to
having several of them declared with
the same name but in different modules; I have also seen similar problems
caused by calling
the create method of a given variable several times, or by assigning its
owner to Nil);
In Delphi, in practice I pack all variables into classes or else declare
them locally within methods,
the only exception being global constants, though I am tending to pack them
into classes or records too:
var global_consts :
record
aa : integer;
bb : integer;
end;
implementation
begin
global_consts .aa = 12;//assign default value
global_consts .bb = 13;
end;
I prefer to use 'global_consts.aa' instead of just 'aa'
because you know what you are referencing (you could have multiples
instances of 'aa')
Typecasting is useful too in dereferencing objectlists, which I often use
for lists of custom object instances:
Type TCourseObjList;: TObjectList; (contains methods for adding/deleting
intances of TCourse)
var Courses: TCourseObjList;
var CurrentCourse: TCourse;
CurrentCourse:= TCourse(Courses[xx]);//xx is course index number
This type of structure is good if a single Student is assigned to multiple
courses (TCourseObjList)
of undetermined number (the TCourseObjList is dynamic);
The advantage of having the TCourseObjList component is that it has its own
methods for internally creating
the TCourse instances and adding them to the list, assigning default values
etc. Once it is tested and functional,
it is used by declaring an instance and using its methods and dereferencing
it: there is little scope for mistakes with pointers
(@CurrentCourse, CurrentCourse, CurrentCourse^ etc) and the possibility of
using Nil pointers by mistake is reduced;
These propositions work well in Delphi and C#, so I presume also in Java and
other OO languages;
Kevin
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