Insert Method infinite loop in a doublylinkedlist - loops

Question

I may just be entirely ignorant to what is happening here but i've looked over it a million times and i'm sure it is something obvious but my insert method infinitely loops due to the while loop. Any help would be appreciated.
Here is the code..
package dcjaniszewskiOL4;
public class DoublyLinkedList<T extends Comparable> {
private class Node<T>
{
private T data;
private Node<T> next;
private Node<T> prev;
private Node(T d){
data=d;
next=null;
prev=null;
}
private Node( T d, Node<T> pref, Node<T> nref){
data=d;
prev=pref;
next=nref;
}
}
private Node<T> head;
private Node<T> current;
private int size;
public DoublyLinkedList(){
head = new Node<T>(null,null,null);
current=head.next;
size=0;
}
public DoublyLinkedList(DoublyLinkedList<T> i){
}
public void insert (T d){
Node<T> ptr, trav, prev;
prev=null;
begin();
trav=head.next;
if(empty()){
head.next = new Node<T>(d,head,head);
}
while(trav!=null){
System.out.println(trav.data);
prev=trav;
advance();
trav=current;
}
ptr = new Node<T> (d, prev,head);
if(prev==null){
head.next=ptr;
head.prev=ptr;
}
else{
prev.next=ptr;
current.prev=ptr;
}
size++;
}
public void remove(T d) throws ListEmptyException, NotInListException{
Node<T> tmp = head;
if(head.next==null){
throw new ListEmptyException("List is empty on Remove");
}
while(tmp!=null){
if(tmp.data.equals(d)){
tmp.prev.next=tmp.next;
tmp.next.prev=tmp.prev;
size--;
}else{
tmp=tmp.next;
if(tmp==null){
throw new NotInListException("Item is not in the list");
}
}
}
}
public void begin(){
current=head.next;
}
public void advance(){
current.prev = current;
current=current.next;
}
public void retreat(){
current.next=current;
current=current.prev;
}
public T current() throws ListEmptyException{
if(current==null){
throw new ListEmptyException("List is empty");
}else{
return current.data;
}
}
public boolean end(){
boolean end = false;
if(current==null){
end=true;
}else{
end=false;
}
return end;
}
public boolean empty(){
boolean empty = false;
if(size()==0){
empty=true;
}else{
empty=false;
}
return empty;
}
public int size(){
return size;
}
}

Answer 1

try this
ptr = new Node<T> (d, null,null);
trav=head;
while (trav.next!= null)
{
trav = trav.next;
}
trav.next = ptr;
ptr.prev = trav;
Let me know if it doesn't work