Implement Queue with doubly linked list

public class MyQueue<T> {

private ListNode<T> head;

private ListNode<T> tail;

private int length;

public MyQueue<T> {

this.head = null;

this.tail = null;

this.length = 0;

}

public void offer(T element) {

ListNode<T> newNode = new ListNode<T>(element);

if (tail == null) {

head = newNode;

tail = newNode;

}

tail.next = newNode;

newNode.prev = tail;

tail = newNode;

length++;

}

public T poll() {

if (head == null) return null;

ListNode temp = head;

if (head == tail) {

head = null;

tail = null;

} else {

head = head.next;

head.prev = null;

temp.next = null;

}

length--;

return temp.item;

}

public T peek() {

if (head == null) return null;

return head.item;

}

}