Can a constructor in Java be private?

I expected that someone would've mentioned this (the 2nd point), but.. there are three uses of private constructors:

• to prevent instantiation outside of the object, in the following cases:

  • singleton
  • factory method
  • static-methods-only (utility) class
  • constants-only class
    .

• to prevent sublcassing (extending). If you make only a private constructor, no class can extend your class, because it can't call the super() constructor. This is some kind of a synonym for final

• overloaded constructors - as a result of overloading methods and constructors, some may be private and some public. Especially in case when there is a non-public class that you use in your constructors, you may create a public constructor that creates an instance of that class and then passes it to a private constructor.

Yes it can. A private constructor would exist to prevent the class from being instantiated, or because construction happens only internally, e.g. a Factory pattern. See here for more information.

Well, if all of your methods in a class are static, then a private constructor is a good idea.