Removing items from queues...

Question

I am almost done with this program, just I cannot remove items from the end of the queue successfully. The object of this program was to remove the first 5 and last 5 items from a queue and print the remaining. I've done all but remove the last 5. There is some code in there to do it, but it doesn't work correctly. I'd appreciate any help. Thank you.
public class Library3
public static void main (String[] args)
BookList3 books = new BookList3();
System.out.println (books);
// add twenty books by addLast
for (int x = 1; x < 21; x++)
books.addLast (new Book("Java " + x));
System.out.println("The first 5 books by \'getFirst()\' are:");
for (int x = 0; x < 5; x++)
System.out.println((Book) books.getFirst());
System.out.println("\nThe first 5 books by \'getLast()\' are:");
for (int x = 0; x < 5; x++)
System.out.println((Book) books.getLast());
System.out.println("\nThere are " + books.size() + " books remaining in the library ");
System.out.println (books);
public class BookList3
private BookNode first, last;
private int size = 0;
BookList3()
first = last = null;
public void add (Book newBook)
BookNode newNode = new BookNode (newBook);
if (first == null) // the queue is empty
first = last = newNode; // first element is also the last
else
last = last.next = newNode; // last link now points to current
public void enqueue (Book newBook)
add (newBook);
public void addLast(Book newBook)
enqueue (newBook);
size++;
public Book dequeue()
if (first == null)
return new Book ("No books to remove");
else
BookNode current = first;
first = first.next;
return current.book;
public Book getFirst()
size--;
return dequeue();
public Book pop()
if (last == null)
return new Book("No books to remove");
else
BookNode current = last;
last = last.previous;
return current.book;
public Book getLast()
size--;
return pop();
public int size()
return size;
public String toString ()
String result = "";
BookNode current = first;
while (current != null)
result += current.book.toString() + "\n";
current = current.next;
return result;
private class BookNode
public Book book;
public BookNode previous, next;
public BookNode (Book theBook)
book = theBook;
previous = next = null;
public class Book
private String title;
public Book (String newTitle)
title = newTitle;
public String toString ()
return title;
}

Answer 1

Just a couple of notes...
- your calls to getLast, getFirst, etc. seem a little redundant. Apart from incrementing the size variable, they just call their respective class to do the action. Both methods are already public, so why the need to call another method? Just throw the size++ or size-- into the implemented method. And your enqueue just calls add() and nothing else... just an unnecessary intermediate step.
- I'm not a big fan of the return new Book ("No books to remove") ... if there are no books, why not return null, and do a check for it on the calling method. Creating a new book to return the fact that there are no books to return just doesn't seem logical. What I guess you're doing is displaying the title of the book if there's a book to return. If not, then you return a book with the title "No books to remove" and it displays that instead. All fine and dandy, but mindsets like that will eventually dig you into a hole. A quick check for null can take care of it, no problem.
Okay, now back to your problem. In what way is it not "working correctly". What is your output onto your screen. The code to pop() (thought Pop was related to Stacks, not Queues, but whatever), enqueue() and dequeue() all look fine at first glance, but I haven't traced the code extensively. I'd say throw in a bunch (and I mean a ton) of println()'s in there, and see if you can figure out where your problem lies. I'd do it, but hey.. it's your project :) If you can't figure out what's going on, post an update on your problems and i'll take another look.