public class Queue<T>
{
    private Node<T> head;
    private Node<T> tail;
    private int size;

    private class Node<T>
    {
        private T thisElement;
        private Node<T> nextElement;

        public Node(T thisElement, Node<T> nextElement)
        {
            this.thisElement = thisElement;
            this.nextElement = nextElement;
        }
    }

    public Queue()
    {
        tail = new Node<T>(null, null);
        head = new Node<T>(null, tail);
        size = 0;
    }

    // Utilities for queue
    public boolean isEmpty()
    {
        return size == 0;
    }

    public int size()
    {
        return size;
    }

    //Insert an element
    public boolean offer(T element)
    {
        if(size == 0)
        {
            head.thisElement = element;
            size++;
        }
        else if(size == 1)
        {
            tail.thisElement = element;
            size++;
        }
        else
        {
            Node<T> temp = new Node<T>(element, null);
            tail.nextElement = temp;
            tail = temp;
            size++;
        }

        return true;
    }

    //Return head but do not remove it, or null if size == 0
    public T peek()
    {
        if(size == 0)
        {
            return null;
        }
        else
        {
            return head.thisElement;
        }
    }

    //Return head but do not remove it, or new Object if size == 0
    @SuppressWarnings("unchecked")
    public T element()
    {
        if(size == 0)
        {
            return (T) new Object();
        }
        else
        {
            return head.thisElement;
        }
    }

    //Return head and remove it, or null if size == 0
    public T pool()
    {
        if(size == 0)
        {
            return null;
        }
        else if(size == 1)
        {
            size--;
            return head.thisElement;
        }
        else
        {
            T tempElement = head.thisElement;
            head = head.nextElement;
            size--;
            return tempElement;
        }
    }

    //Return head and remove it, or new Object if size  ==  0
    @SuppressWarnings("unchecked")
    public T remove()
    {
        if(size == 0)
        {
            return (T) new Object();
        }
        else if(size == 1)
        {
            size--;
            return head.thisElement;
        }
        else
        {
            T tempElement = head.thisElement;
            head = head.nextElement;
            size--;
            return tempElement;
        }
    }
}