title: Intersection of two sets
body: <p>Is easy way to get the intersection of two sets? 
  I have: </p>
  
  <pre><code>    Set&lt;Long&gt; set1 = {1,2,3}
      Set&lt;Long&gt; set2 = {2,3,4}
  </code></pre>
  
  <p>And I looking or method like:</p>
  
  <pre><code>    Set&lt;Long&gt; intersection = new HashSet&lt;&gt;();
      intersection.intersect(set1, set2);
  </code></pre>
  
  <p>And intersection.toString() produce me set contains {2,3}</p>