title: How to implement Java 8 Stream API using Java 7 or older?
body: <p>I was asked this question in a job interview (Microsoft).<br>
  methods to implement for example:<br>
   <strong>.stream(), .filter(), .map() , flatMap() , min() , count() , reduce() , groupBy()</strong><br>
  etc</p>
  
  <p>It's quite an open question but I think is an interesting one.</p>
  
  <p>Thanks</p>