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Posted by Daedalus.OS on 10/13/92 11:30
Well that's exactly where I took this idea from, some article about Design
Patterns.
I got really interesting answers and it help me a lot... I got my books now
but I will certainly have some questions about OOP in the future.
Thanks to all of you.
Dae
>> If you think about it, it is quite odd. The constructor is never called
>> directly, but it is a language construction. You give a "new" keyword,
>> some space in memory is reserved, the class name is attached to it as a
>> type, and its constructor is called. By whom? By the virtual machine
>> itself, basically.
>
>> Making it private is _really_ odd.
>
> Actually, it's a *very* common design pattern in many OO languages.
>
>> It is not very consequent either. "private" in java means "visible only
>> within the same instance". Only for constructors it suddenly means
>> "visible within the same class".
>
> Not true. "Private" means visible within the same class, e.g.:
>
> class Foo
> {
> private $v;
>
> function bar($theFoo)
> {
> echo $theFoo->$v;
> }
> }
>
> $a = new Foo;
> $b = new Foo;
> $b->bar($a);
>
> The equivalent works in Java, C++ and C#.
>
>
>> Declaring it abstract will certainly stop instantiation. However,
>> "abstract", communicates that it is meant as a superclass. I would not
>> create a constructor at all and not declare it abstract either. As the
>> static operator differs from the normal method calling, it is clear
>> enough that instantiation is pointless. Any instance does not have
>> properties or methods that can be called on it.
>
> One of the ideas of writing good OO code is to explicitly enforce a
> well-defined interface on your classes' users, i.e. what they can and
> can't do with it. If you don't want them to be able to instantiate a Foo,
> enforce it with a private constructor, don't leave it to chance.
>
> Another example would be, if it makes no semantic sense for a Foo to ever
> be extended, explicitly say so with the "final" keyword.
>
>
>
> --
> Oli
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