FUDforum
Fast Uncompromising Discussions. FUDforum will get your users talking.
Home » Imported messages » comp.lang.php » out of sheer curiosity...
Show: Today's Messages :: Polls :: Message Navigator
Return to the default flat view Create a new topic Submit Reply
Re: out of sheer curiosity... [message #177623 is a reply to message #177619] Tue, 10 April 2012 23:50 Go to previous messageGo to previous message
Jerry Stuckle is currently offline  Jerry Stuckle
Messages: 2598
Registered: September 2010
Karma:
Senior Member
On 4/10/2012 5:57 PM, Thomas Mlynarczyk wrote:
> Jerry Stuckle schrieb:
>
>> Although not a separate entity, the parent is still considered an
>> object. You can, for instance, call public methods which are defined
>> in the parent but not the child. Those methods will operate on the
>> parent, just as if you had a parent object.
>
> Hm. Makes sense.
>
>> So basically what you have is "dual identity" - the object is
>> considered both a parent and a child, depending on the context.
>
> Yes, thinking more about it, it becomes a bit clearer. A child is also
> an instance of all of its parent classes.
>
>> And the parent's constructor is responsible for constructing the
>> parent object; the child is only responsible for constructing the
>> child object.
>
> So the parent has a "private part" and the child has a "private part",
> but they might also have a "shared part" ("protected") and there both
> child and parent are responsible.
>

Generally, protected variables are frowned upon. Remember - ANYTHING
exposed outside the class can never be changed once the class is put
into production. You don't know how it will affect other classes.

Also, protected member variables leave the possibility open that a child
class can place an invalid value in it, potentially corrupting the base
class.

Private members (both variables and methods) and the code in the methods
are never available outside the class. As long as the result is the
same, how the class is implemented is immaterial.

This can be very handy when prototyping, for instance. You can create a
"quick and dirty" implementation of the class and use it. Later you can
come back and clean it up, making it more efficient, etc.

> If the child overwrites a parent method, this will also affect the
> parent since $this->method() will refer to the child's method, even if
> called from a method defined in the parent class.
>

Nope. If it's important to the parent, then the child's method should
call the parent's method. But many times I've had methods in the child
class which don't call the parent method for various reasons.

>> This is actually quite important. This allows you to change the
>> implementation (code and private variables) of the parent object
>> without affecting any child objects.
>
> So if there is no "shared part" between parent and child, does that mean
> the child class should not have been derived from the parent in the
> first place? Like "nothing to share -- nothing to inherit"?
>
> Greetings,
> Thomas
>

There is always something to inherit - the public interface. But the
child class should always be a more specific instance of the parent
class. For instance, Person->Employee would be ok, because Employee is
a more specific instance of Person. However, Employee->Contractor would
not - a contractor is not an employee.

The Person class can have private members for name, address, etc.
Employee would have additional fields such as start_date, employee_id, etc.

And from Employee you could derive Manager.

--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex(at)attglobal(dot)net
==================

Report message to a moderator

[Message index]
 
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Read Message
Previous Topic: 5.4 windows installer.
Next Topic: Does PHP5 treat $_SERVER['PHP_AUTH_USER']) differently?
Goto Forum:
  

-=] Back to Top [=-
[ Syndicate this forum (XML) ] [ RSS ]

Current Time: Fri Nov 22 14:31:30 GMT 2024

Total time taken to generate the page: 0.05407 seconds
.:: Contact :: Home ::.

Powered by: FUDforum 3.1.3.
Copyright ©2001-2023 FUDforum Bulletin Board Software