import java.util.*;

public class ListQueue implements Queue
{
    public ListQueue()
    {
        list = new LinkedList();
    }
    public void enqueue(Object x)
    {
        list.addLast(x);
    }
    public Object dequeue()
    {
        return list.removeFirst();
    }
    public Object peekFront()
    {
        return list.getFirst();
    }
    public boolean isEmpty()
    {
        return list.size() == 0;
    }
    private LinkedList list;
}