Java How to Program, Early Objects, 11th Edition

21.2 Self-Referential Classes

A self-referential class contains an instance variable that refers to another object of the same class type. For example, the generic Node class declaration

class Node<E> { 
   private E data;
   private Node<E> nextNode; // reference to next linked node
   public Node(E data) { /* constructor body */ }
   public void setData(E data) { /* method body */ }
   public E getData() { /* method body */ }
   public void setNext(Node<E> next) { /* method body */ }
   public Node<E> getNext() { /* method body */ } 
}

has two private instance variables—data (of the generic type E) and Node<E> variable nextNode. Variable nextNode references a Node<E> object, an object of the same class being declared here—hence the term “self-referential class.” ...