1. insertNode
    2. insertFront
    3. insertLast
    4. removeLast
    5. removeFront
    6. printNode

    See File: 
    $j/JavaSingleLinkedList.java

    public static void printNode(Node head){
        Node curr = head;
        while(curr != null){
            pl(curr.toString());
            curr = curr.next;
        }
    }
    public static Node insertNode(Node head, Node node){
       if(head == null){
           head = node;
       }else{
            Node curr = head;
            Node prev = null;
            while(curr.next != null){
               curr = curr.next;
            }
            curr.next = node;
       }
       return head;
    }

    public static Node insertFront(Node head, Node node){
        if(head == null){
            head = node;
        }else{
            node.next = head;
            head = node;
        }
        return head;
    }

    public static Node insertLast(Node head, Node node){
        if(head == null){
            head = node;
        }else{
            Node curr = head;
            while(curr.next != null){
                curr = curr.next;
            }
            curr.next = node;
        }
        return head;
    }

    public static Node removeFront(Node head){
        if(head == null){
            // Nothing to remove
        }else{
            Node h2 = head.next;
            head = h2;
        }
        return head;
    }
    public static Node removeLast(Node head){
        if(head == null){
            // Nothing to remove
        }else{
            Node curr = head;
            Node prev = null;
            while(curr.next != null){
                prev = curr;
                curr = curr.next;
            }
            if(prev == null){  // Only one node
                head = null;
            }else{
               prev.next = null; 
            }
        }
        return head;
    }