Private constructor in abstract class

Question

In Java what is the purpose of using private constructor in an abstract class?

In a review I got this question, and I am curious, for what situation we need to use

Answer 1

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).

It does look like we will be getting sealed interface to more cleanly support this. See https://openjdk.java.net/jeps/8222777