title: How do I pass an ArrayList to method that takes a collection as an input
body: <p>I want to pass some <code>ArrayList&lt;Integer&gt;</code> X into method <code>a(Collection&lt;Integer&gt; someCol)</code> that takes <code>Collection&lt;Integer&gt;</code> as an input.</p>
  
  <p>How can I do this? I thought an ArrayList was a Collection and thus I should be able to "just do it" but it seems that Collection is an interface and ArrayList implements this interface. Is there something I can do to make this work ... if you understand the theory that would also help me and possibly lots of other people.</p>
  
  <p>Thanks</p>