The use of private constructor is to serve singleton classes. A singleton class is one which limits the number of objects creation to one. Using private constructor we can ensure that no more than one object can be created at a time..
Furthermore, why would you use a private constructor?
Private constructors are used to prevent creating instances of a class when there are no instance fields or methods, such as the Math class, or when a method is called to obtain an instance of a class. If all the methods in the class are static, consider making the complete class static.
Also, can we define constructor as private? Yes, class can have a private constructor. It is needed as to disallow to access the constructor from other classes and remain it accessible within defined class. A singleton is a design pattern that allows only one instance of your class to be created, and this can be accomplished by using a private constructor.
Likewise, what happens if we make constructor private?
With private constructor instance of that class can only be created inside declaring class . By making a constructor private, we can prevent a class from being extended by any other class. To limit the number of instance creation. To give meaningful name for object creation using static factory method.
Can we create object of private constructor in Java?
Yes we can have private constructors in a class and yes they can be made accessible by making some static methods which in turn create the new object for the class. So to make an object of this class, the other class has to use the static methods.
Related Question Answers
Can constructor be inherited?
Constructors are not members of classes and only members are inherited. You cannot inherit a constructor. That is, you cannot create a instance of a subclass using a constructor of one of it's superclasses.Can a constructor be final?
No, a constructor can't be made final. A final method cannot be overridden by any subclasses. In other words, constructors cannot be inherited in Java therefore, there is no need to write final before constructors. Therefore, java does not allow final keyword before a constructor.Can a constructor be static?
constructor is implicitly called to initialize an object, so there is no purpose in having a static constructor. Java does not permit to declare a constructor as static. A constructor always belongs to some object. If a constructor is static, an object of subclass cannot access.What is the difference between static and private constructor?
Static Constructor is called automatically before the first instance of the class or any static data is referenced. It is called only once for any number of classes instance is created. Private constructor is a special constructor that generally used in class that contains only static members.Can we override private methods?
No, a private method cannot be overridden since it is not visible from any other class. You have declared a new method for your subclass that has no relation to the superclass method. One way to look at it is to ask yourself whether it would be legal to write super.Can a class with private constructor be inherited?
If class with private constructor and sealed class cannot be inherited , then what is the use of class which cannot be inherited. And as said previously private constructor can be excused as we have static classes now. So private constructor + sealed means pure static class. Also sealed class cannot be inherited.Can a constructor be protected?
protected constructor can be accessed from its own class, its subclasses, all other classes belonging to the same package and subclasses of other packages. A class with both private and protected constructors available can be inherited; but subclass has the accessibility for protected constructors only.Can we override static method?
Static methods cannot be overridden because they are not dispatched on the object instance at runtime. The compiler decides which method gets called. Static methods can be overloaded (meaning that you can have the same method name for several methods as long as they have different parameter types).Can I declare constructor as private?
The use of private constructor is to serve singleton classes. Using private constructor we can ensure that no more than one object can be created at a time. By providing a private constructor you prevent class instances from being created in any place other than this very class.Can copy constructor be private?
Yes, a copy constructor can be made private. When we make a copy constructor private in a class, objects of that class become non-copyable.Can constructor return a value?
Constructors cannot return a value; they return the constructed object, so to speak. You get an error because the compiler is looking for a constructor that takes a string as its argument. A class contains constructors that are invoked to create objects from the class blueprint.Can we use this () and super () in a method?
this() and super(), both are the constructors that's why must be the first statement. But we can use both in a program. this(): It is used to call, same class Default or Parametrized Constructor. super(): It is used to call, immediate super/parent class Default or Parametrized Constructor.Can abstract class have private constructor?
A private constructor in an abstract class can also serve the purpose of sealed classes (like in Scala or Kotlin etc.). Since you can still provide subclasses from within the abstract class, but outsiders cannot extend/implement (as @Marko Topolnik answered).Should a constructor be public or private?
No, Constructors can be public , private , protected or default (no access modifier at all). Making something private doesn't mean nobody can access it. It just means that nobody outside the class can access it. So private constructor is useful too.Can you use both this () and super () in a constructor?
this() calls another constructor in the same class whereas super() calls a super constructor. So both are constructor calls. Constructor must always be the first statement. So we can not have two statements as first statement, hence either we can call super() or we can call this() from the constructor, but not both.What is constructor in OOP?
A constructor is a special method of a class or structure in object-oriented programming that initializes an object of that type. A constructor is an instance method that usually has the same name as the class, and can be used to set the values of the members of an object, either to default or to user-defined values.Can static class have private constructor?
A static constructor does not take access modifiers or have parameters. A class or struct can only have one static constructor. Static constructors cannot be inherited or overloaded. A static constructor cannot be called directly and is only meant to be called by the common language runtime (CLR).What happens if constructor is private in C++?
If some constructor is private, it means that no one but the class itself (and friends) should be able to create instances of it using that constructor. Therefore, you can provide static methods like getInstance() to create instances of the class or create the instances in some friend class/method.Is constructor public or private in C++?
If a constructor is not provided to a class in C++, the compiler adds a default 'public' constructor. However if a constructor is provided and is declared as private, that would imply that the object of the class cannot be created outside the class scope. 
William Jenkins 
