import javafx.collections.ModifiableObservableListBase;

import java.util.Iterator;

public class LinkedQueue<E> extends ModifiableObservableListBase<E> implements Iterable<E>, SimpleQueue<E> {

private LinkedQueueNode<E> front;

private LinkedQueueNode<E> rear;

private int size = 0;

@Override
public E get(int index) {

   LinkedQueueNode<E> tmp = front;
   int count = 0;
   boolean found = false;
   while (tmp != null){
         if(count++ == index){
            found = true;
            break;
         }
         tmp = tmp.getNext();
   }
   if(!found){
         throw new IndexOutOfBoundsException();
   }
   return tmp.getData();
}

@Override
public void enqueue(E element) {
   LinkedQueueNode<E> node = new LinkedQueueNode<E>(element, null);
   if(rear == null){
         rear = node;
         front = node;
   }else {
         rear.setNext(node);
         rear = node;
   }
   size++;
}

@Override
public E dequeue() {
   if(front != null){
         E data = front.getData();
         front = front.getNext();
         size--;
         if(size <= 0){
            clear();
         }
         return data;
   }
   return null;
}

@Override
public boolean isEmpty() {
   return size == 0;
}

Consider a class Fraction of fractions. Each fraction is signed and...