ADTQueue with circular doubly linked list

I have written these codes and in trying out the code in my main method, it looks like I am on the right way, but which disturbs me is the fact, that whenever I say:

while (!empty(){

it give me front of the queue. It seems like the queue never gets empty and the loop is running forever. Is this the logic of circular doubly linked lists, that it never gets empty? I think I might be making mistakes in the dequeue method.

package übung;

import java.util.NoSuchElementException;

public class QueueCircularDLL<T> implements ADTQueue<T> {
private ListElement<T> head;
private ListElement<T> tail;

public QueueCircularDLL(){
    head=null;
    tail=null;
}

public void enq (T element){
    ListElement<T>newElement=new ListElement<T>(element);
    if (empty()){
        head= newElement;
        tail= head;
    }

    tail.setNextElement(newElement);
    newElement.setPrevElement(tail);
    tail=tail.getNextElement();
    tail.setNextElement(head);
    head.setPrevElement(tail);

}

    public void deq(){
    if (empty()){
        throw new RuntimeException("queue is empty");
    }

    if (head==tail){
        //head=null;
        head=null;
        tail=null;

    }
    else{
    head=head.getNextElement();
    head.setPrevElement(tail);
    tail.setNextElement(head);
    }

}

public T front(){
    if(empty()){
        return null;
    }
    return head.getElement();
}

public boolean empty(){
    return (head==null);
}

private static class ListElement<T>{
    private T element = null;
    private ListElement<T> nextElement = null;
    private ListElement<T> prevElement = null;

    public ListElement(T element) {
        this.element = element;
    }

    public T getElement() {
        return element;
    }

    public ListElement<T> getNextElement() {
        return nextElement;
    }

    public void setNextElement(ListElement<T> element) {
        this.nextElement = element;
    }
    //für zirkuläre doppelt verkettete liste
    public ListElement<T>getPrevElement(){
        return prevElement;
    }
    // für zirkuläre doppelt verkette liste
    public void setPrevElement(ListElement<T> element){
        this.prevElement=element;
    }



}

public static void main(String[] args) {
    QueueCircularDLL<Integer> queue = new QueueCircularDLL<Integer>();

    for (int i = 0; i < 10; ++i) {
        queue.enq(i);
    }

    //while (!queue.empty()) {
    for(int i=0; i<20; i++){
        System.out.println(queue.front());
        queue.deq();
    }
}


}