if I declare a constructor as private can i call this constructor in another class

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If I declare a constructor as private can I call this constructor in another class?

class A{

private A(){

...
}


class B {

A  a_obj=new A(){}           //shows an error--not visible 

}

I want to declare a private constructor anyhow, I can't violate that, but still can I use it in other way around?

Posted 16-Feb-11 20:49pm

ziaur25

Updated 16-Feb-11 21:39pm

Dalek Dave

v3

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Dalek Dave 17-Feb-11 3:39am

Edited for Grammar.

2 solutions

Solution 2

Not only you cannot instantiate a class with all constructors private (not from outside of the class, but class can provide a factory creating an instance), but this is also a well known method of programming.

In particular, this is the only way to created functionality of abstract classes (there is no "abstract" keyword in C++, in contrast to newer OOP languages). Such classes are very useful it a class hierarchy needs a common base class with common functionality which can only be used as a base class; an accidental attempt to create an instance of such class with be prevented by compiler.

—SA

Posted 16-Feb-11 21:56pm

Sergey Alexandrovich Kryukov

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Manfred Rudolf Bihy 17-Feb-11 5:00am

Good answer! 5+

Sergey Alexandrovich Kryukov 17-Feb-11 20:07pm

Thank you.
--SA

Espen Harlinn 17-Feb-11 9:26am

Factory methods are a well-known pattern, my 5.

Abstract methods in c++ are called pure virtual functions.
class Abstract {
public:
virtual void pure_virtual() = 0;
};

Sergey Alexandrovich Kryukov 17-Feb-11 20:07pm

Thank you for the note, I should have mentioned that in my Answer.
The thing is: it does not make whole class abstract (and in C# would not compile).
--SA

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Venkatesh Mookkan · Accepted Answer · 2011-02-16T21:08:00

Solution 1

You cannot initialize a object using private constructor.

Please see this[^]

Posted 16-Feb-11 21:08pm

Venkatesh Mookkan

Comments

Dalek Dave 17-Feb-11 3:39am

Good Link.

Venkatesh Mookkan 17-Feb-11 3:41am

Thanks DD