/** An instance is a node of a doubly linked list */
public class ListNode {
    /** name of previous node (null if none) */
    public ListNode prev; 
    
    /** the value of this node */
    public Object element;
    
    /** name of next node (null if none) */
    public ListNode next; 
    
    /** Constructor: a ListNode with element e, prev field p, 
        and next field n */
    public ListNode(ListNode p, Object e, ListNode n){
        prev= p; element= e; next= n;
    }

}