title: Java many arraylists - find common element
body: <p>I have an application that generates many arraylists, stored in a collection. All the arraylists will always have a common element.</p>
  
  <p>I need to work out which is the common element. I managed this with two lists and using <code>List.contains(...)</code> but need to scale this to many lists.</p>
  
  <p>How can I do this? </p>