/**
* Returns value of the element that was first added to the queue.
*
* @return value stored in the head of the queue.
*/
@Override
public Item peek() {
if (head == null) {
throw new IllegalStateException("Queue cannot be empty.");
}
return head.data();
}
/** Accesses next element in the queue. */
@Override
public Item next() {
if (!hasNext()) {
throw new NoSuchElementException("Queue cannot be empty.");
} else {
Item returnValue = current.data();
toRemoveLink = current;
current = current.previous();
markNext = true;
--index;
return returnValue;
}
}
/**
* This method removes the first element added to the queue.Since it's not a circular linked
* queue, it has to handle special case when there is only one element in the queue.
*
* @return returnValue removed data element.
*/
@Override
public Item dequeue() {
if (size == 0) {
throw new IllegalStateException("Queue cannot be empty.");
}
// ~Creates a variable to store a current data, that is removed by
// dequeue()
Item returnValue = head.data();
// ~Special case, where there is only one element in the queue.
if (size == 1) {
back = null;
head = null;
--size;
return returnValue;
} else { // Changes value of head of the current queue.
head = head.previous();
head.split();
--size;
return returnValue;
}
}
