Can we have a private constructor ?
Answers were Sorted based on User's Feedback
Answer / srikanth
We can make a constructor Private or protected.
1. Private constructor is classic example of implementing a
singleton class( A class with a single instance)
2. Protected constructors can be used when the class cannot
be instantiated but can only be inherited.
Is This Answer Correct ? | 108 Yes | 2 No |
Answer / prabha govind
yes
and if a constructor is made private/protected...then that
class cannot be inherited
Is This Answer Correct ? | 116 Yes | 23 No |
Answer / baikunta
yes , we can creat private constructor trrough static
method we can access the class (constructor), for example
singleton, there are a lot of use in design pattern
here is example of single ton
class Singleton {
static Singleton s;
int i;
Singleton(int x) : i(x) { }
void operator=(Singleton&);
Singleton(const Singleton&);
public:
static Singleton& getHandle() {
return s;
}
int getValue() { return i; }
void setValue(int x) { i = x; }
};
Singleton Singleton::s(47);
int main() {
Singleton& s = Singleton::getHandle();
cout << s.getValue() << endl;
Singleton& s2 = Singleton::getHandle();
s2.setValue(9);
cout << s.getValue() << endl;
} ///:~
Is This Answer Correct ? | 34 Yes | 1 No |
Answer / arun
1. Yes we can make a constructor private. By implementing
this concept we can create a singleTon class.
2. Suppose we have a static method is a class that is used
to create the object of the class by using private
constructor then that member function is named as "Named
Constructor".
3. Using this named constructor concept we can create
SingleTon class as well as normal class.
Example:
class Singleton
{
public:
static Singleton* Instance();
protected:
Singleton();
Singleton(const Singleton&);
Singleton& operator= (const Singleton&);
private:
static Singleton* pinstance;
};
Singleton* Singleton::pinstance = 0;// initialize pointer
Singleton* Singleton::Instance ()
{
if (pinstance == 0) // is it the first call?
{
pinstance = new Singleton; // create sole instance
}
return pinstance; // address of sole instance
}
Singleton::Singleton()
{
//... perform necessary instance initializations
}
Singleton *p1 = Singleton::Instance();
Singleton *p2 = p1->Instance();
Singleton & ref = * Singleton::Instance();
Is This Answer Correct ? | 25 Yes | 0 No |
Answer / arun
#include<iostream>
using namespace std;
class Singleton
{
public:
static Singleton* Instance();
private:
static Singleton* pinstance;
Singleton();
};
Singleton* Singleton::pinstance = 0;// initialize pointer
Singleton* Singleton::Instance ()
{
if (pinstance == 0) // is it the first call?
{
pinstance = new Singleton; // create sole instance
}
return pinstance; // address of sole instance
}
Singleton::Singleton()
{
//... perform necessary instance initializations
}
void main()
{
Singleton *p1 = Singleton::Instance();
cout<<p1<<endl;
Singleton *p2 = p1->Instance();
cout<<p2<<endl;
Singleton & ref = * Singleton::Instance();
}
Is This Answer Correct ? | 9 Yes | 4 No |
Answer / aj
Yes, only if we want to prevent instantiation from other
class, but then the class itself cannot be sub classed.
this the heart of singleton design pattern
Is This Answer Correct ? | 3 Yes | 1 No |
#include<iostream>
using namespace std;
class A
{
int value;
A* ptr;
A()
{
cout<<"\n\t\tConctructor\n";
}
public:
static A* CreateObject()
{
A* ptr=NULL;
ptr=new A;
return ptr;
}
void getdata()
{
cout<<"\n\tEnter the Value of A class\t:\t";
cin>>value;
}
void putdata()
{
cout<<"\n\t\tThe Value of A Class\t:\t";
cout<<value<<endl;
}
~A()
{
cout<<"\n\t\tDestructor\n";
}
};
int main()
{
A *ptr,*ptr1,*ptr3;
ptr=A::CreateObject();
ptr1=A::CreateObject();
ptr3=A::CreateObject();
ptr->getdata();
ptr1->getdata();
ptr3->getdata();
ptr->putdata();
ptr1->putdata();
ptr3->putdata();
delete ptr;
delete ptr1;
delete ptr3;
return 0;
}
Ref:
Singleton and Factory
Classes...
Is This Answer Correct ? | 3 Yes | 5 No |
Answer / ashwini
Yes, We can.
By doing so, we can create only single instance of the
class.(singleton)
Is This Answer Correct ? | 0 Yes | 6 No |
Answer / arpitha
no, its of no use having a private constructor,,, bcoz
declaring constructor as private makes it blocked.
Is This Answer Correct ? | 6 Yes | 24 No |
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