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Constructor in private

 
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Hi All,
I read in some book that "Math constructor is private, cannot be instantiated." Is this correct? If costructor is in private section, can't we create an instance? I tried this, its working fine. If costroctor is in private section, its not possible to Extend that class. Any information on this....
regards,
sri.
 
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If a constructor in a class definition is private, then you cannot create an instance of that class using that constructor outside of the class definition. If a class is declared final, then you can't extend it.
 
sri rallapalli
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If that is the case just check this code. Here constructor is in Private, and i am creating an object with that costructor.

public class Temp
{
private Temp()
{
System.out.println("Hello Rallapalli");
}
public void f()
{
int a=10;
System.out.println(a);
}
public static void main(String [] args)
{
Temp t = new Temp();
t.f();
}
}

According to ur explanation, it should not create an instance. But it is creating and working fine.
Please let me know.
regards,
sri.
 
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Originally posted by sri rallapalli:

According to ur explanation, it should not create an instance. But it is creating and working fine.
Please let me know.
regards,
sri.



Keith explanation is correct, but I'll give it another try.

A private constructor means that it is private. It can only be used by that class. For example, only code in the Math class can instantiate a Math object, because it is private to the Math class.

Anyway, try to instantiate a Temp object from another class -- you should not be able to.

Henry
 
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Just in addition to Henry's reply.

His explanation is valid for private members as well. So if you try to create an instance of the same class inside the same class you will be able to access its private members. On the other hand, if you try to create an instance for that class inside another class, for sure you will not be able to access its private members.
 
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Just to remind that this kind of pattern is often used in J2EE called Singleton Pattern.


Regards,
Narendranath
 
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Yes, its true...

Private constructor will not allow to instantiate from another class...
but it will allow from within its class...

I learned one more point...

Thank u...

Devisri.
 
With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.
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