public class LinkedList {
    private Node first;
    private Node last;
    private Node current;

    public LinkedList() {
        first = last = current = null;
    }

    public boolean isEmpty() {
        return (first == null);
    }

    public void insertAtFront(Object insertItem) {
        Node newNode = new Node(insertItem);
        if(isEmpty()) {
            first = newNode;
            last = newNode;
        }
        else {
            newNode.next = first;
            first = newNode;
        }
    }

    public void insertAtBack(Object insertItem) {
        Node newNode = new Node(insertItem);
        if(isEmpty()) {
            first = newNode;
            last = newNode;
        }
        else {
            last.next = newNode;
            last = newNode;
        }
    }

    public Object removeFromFront() {
        Object removeItem = null;
        if(isEmpty) {
            return removeItem;
        }
        removeItem = first.data;
        if(first == last) {
            first = last = null;
        }
        else {
            first = first.next;
        }
        return removeItem;
    }

    public Object removeFromBack() {
        Object removeItem = null;
        if(isEmpty()) {
            return removeItem;
        }
        removeItem = last.data;
        if(first == last) {
            first = last = null;
        }
        else {
            current = first;
            while(current.next != last) {
                current = current.next;
            }
            last = current;
            last.next = null;
        }
        return removeItem;
    }

    public Object getFirst() {
        if(isEmpty()) {
            return null;
        }
        else {
            current = first;
            return current.data;
        }
    }
    public Object getNext() {
        if(current == last) {
            return null;
        }
        else {
            current = current.next;
            return current.data;
        }
    }
}