title: Java streams: Map<Enum, List<A>> to List<B>
body: <p>I want to do the following using Java streams:</p>
  
  <p>I have a <code>Map&lt;Enum, List&lt;A&gt;&gt;</code> and I'd like to transform it to <code>List&lt;B&gt;</code> where <code>B</code> has the properties <code>Enum, A</code>.</p>
  
  <p>So for every key and every item in the list of that key I need to make an item <code>B</code> and to collect all of them to a <code>List&lt;B&gt;</code>.</p>
  
  <p>How can it be done using Java streams?</p>
  
  <p>Thanks!</p>