Java Notes: Simple Linked List Exercise 1

import java.util.Scanner;

public class SimpleDoublyLinkedList {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        Elem2 front = null;    // First element of list.
        Elem2 back  = __________;    // Last element of list.
        
        //... Read a list of words.
        while (in.hasNext()) {
            String word = in.next();
            
            Elem2 e = new __________();     // Create a new list element.
            e.__________ = word; 
            
            if (front == null) {
                //... List is empty
                __________ = e;
            } else {
                //... We already have elements.
                back.next = __________; 
            }
            e.prev = __________;
            back = __________; 
        }
        
        System.out.println("*** Print words in order of entry");
        for (Elem2 e = front; e != null; e = e.__________) {
            System.out.println(e.data);
        }
        
        System.out.println("*** Print words in reverse order of entry");
        for (Elem2 e = __________; e != __________; e = e.__________) {
            System.out.println(e.data);
        }
    }
}

////////////////////////////////////////////////////////////////////////// Elem2
class Elem2 {
    public Elem2 next;   // Link to next element in the list.
    public Elem2 prev;   // Link to the previous element.
    public String data;  // Reference to the data.
}