public void setPrev(DoublyLinkedListNode prev)
 {
     this.prev = prev;
 }
 public void setNext(DoublyLinkedListNode next)
 {
     this.next = next;
 }
 public void setValue(double value)
 {
     this.value = value;
     this.prev  = null;
     this.next  = null;
 }