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What is Private Constructor? and it's use? Can you create instance of a class which has Private Constructor?

Posted By :Amit Mehra     Posted Date :September 07, 2008    Points :10   Category :.NET Framework 
When a class declares only private instance constructors, it is not possible for classes outside the program to derive from the class or to directly create instances of it. (Except Nested classes)
Make a constructor private if:

1) You want it to be available only to the class itself. For example, you might have a special constructor used only in the implementation of your class' Clone method.

2) You do not want instances of your component to be created. For example, you may have a class containing nothing but Shared utility functions, and no instance data. Creating instances of the class would waste memory.

You can also find related Interview Question to What is Private Constructor? and it's use? Can you create instance of a class which has Private Constructor?  below: 

Whether we can create a private constructor for a class?

  
Yes it is possible. we can create a private constructor for a class (More...)

What is a private constructor? Where will you use it?

  
When you declare a Constructor with Private access modifier then it is called Private Constructor. We can use the private constructor in singleton pattern.

If you declare a Constructor as private then it doesn't allow to create object for its derived class, i.e you loose inherent facility for that class. (More...)

A constructor can be private. True or False

  
False. A constructor should not be private. (More...)

Where we can use the private constructor?

  
A private constructor is a special instance constructor. It is commonly used in classes that contain static members only. (More...)

Which design pattern should have private or protected constructor?

  
singleton design pattern should have private or protected constructor (More...)

What is the use of private constructor in Java?

  
A private constructor is used when there is no requirement of another class to invoke that. It is used mostly in implementing singletons. A static method is used for managing the creating the instances of that class.

The following is the example of private constructor.

public class Singleton {
private static Singleton instance;.
//private constructor
private Singleton {
// some code goes here
}
} (More...)

How Many Constructor we can create in side the class.

  
we can create more constructor inside the class (More...)

Difference between type constructor and instance constructor? What is static constructor, when it will be fired? And what is its use?

  
(Class constructor method is also known as type constructor or type initializer)
Instance constructor is executed when a new instance of type is created and the class constructor is executed after the type is loaded and before any one of the type members is accessed. (It will get executed only 1st time, when we call any static methods/fields in the same class.) Class constructors are used for static field initialization. Only one class constructor per type is permitted, and it cannot use the vararg (variable argument) calling convention. (More...)

Are private class-level variables inherited?

  
Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are. (More...)

Are private class-level variables inherited?

  
Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are. (More...)

Can namespace contain the private class?

  
no, having a single private class does not mean anything , it is applicable only in case of nested class.
(More...)

How can you access a private method of a class?

  
Use .Net Reflection. Using reflection we can invoke private methods too.

Example:

Car car = new Car();
Type type = car.GetType();
MethodInfo methodInfo = type.GetMethod("ShiftGearUp", BindingFlags.NonPublic | BindingFlags.Instance);
methodInfo.Invoke(car, null);

Pre: Create a class Car with private method "ShiftGearUp" (More...)

In which order the constructor is called for an inherited class?

  
Constructor of Parent class is called

Then,

Constructor of Child class (More...)

Are private class-level variables inherited?

  
Yes,private class members are inheritable, but they are not accessible (More...)

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