Posted by Jerry Stuckle on 11/21/72 11:30

Dikkie Dik wrote:
> Daedalus.OS wrote:
>
>
>
> The PHP help does not say anything about private constructors. I guess
> it is a java thing to make them private to disallow instantiation. 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. As the object is
> still unreferenced, _no_ object can call it (the reference is only
> returned when the constructor has finished). Even the object itself
> cannot call it, as it is still in the process of coming to existence.
> 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".
> 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.
>

Actually, it's not uncommon to have *some* constructors be private. If
all of them are private, you can only instantiate the class through a
static function.

But for instance - it's not unusual in C++ to have a copy constructor be
private. It means the following code will fail:

MyClass a; // Default constructor
MyClass b = a; // Copy constructor - fails if it is private



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Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
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