Question

Say I define a class that has as a member a variable of the same type as itself.

public class Abc {
    private Abc p;
}

This actually works, much to my surprise.

Why I think it shouldn’t: creating an instance of Abc, it contains a variable of type Abc, which contains a variable of type Abc, which contains a variable of type Abc, which …..

Obviously I’m wrong, could someone enlighten me as to how?

Answer 1

You’re only declaring the variable and not creating it. Try creating it at declaration or in the constructor and let me know what happens:

public class Abc {
   private Abc p = new Abc(); // have fun!

   public static void main(String[] args) {
      new Abc();
   }
}

Incidentally, if you don’t create it in the class, but rather accept a reference to it in a getter method or a constructor parameter, your code will work just fine. This is how some linked lists work.