title: How to remove elements in an arraylist start from an indicated index
body: <p>As the picture shown, after one time run a method, i want remove the old items, and prepared for next time calculation, but i wondering how to remove elements in an arraylist start from an indicated index, like a queue, obey FIFO algorithm?
  <img src="https://i.stack.imgur.com/Ptm3j.png" alt="q1"></p>