Use of protected construtor?

[Thiru Thangavelu]

Why constructor is declared with different modfiers? I know that constructors are not inherited and what is the use to declare with diff. modifiers?

[Thomas Paul]

A private constructor prevents the class from being instantiated (see the Math class). A class with protected constructors could only be instantiated by a child of that class or by a class within the same package as that class.
jls:

A protected constructor of an object may be accessed from outside the package in which it is declared only by code that is responsible for the implementation of that object.

[Thiru Thangavelu]

Thanks Paul, but most of the constructors are public(to be accessed anywhere) or default(to be accessed in the same package). Isn't?

[Thomas Paul]

Yes, most are.