A private constructor is a special instance constructor. It is commonly used in classes that contain static members only. If a class has one or more private constructors and no public constructors, then other classes (except nested classes) are not allowed to create instances of this class

Private constructors are used to prevent the creation of instances of a class when there are no instance fields or method, 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 entire class static