title: Combine two lists with no duplicates
body: <p>I want to add the items from a list to another list without any duplicates. I've used the method below involving a set. Is this the most efficient way to achieve the end result? Is there a neater way of updating lista to contain the unique setboth objects?</p>
  
  <pre><code>Set setboth = new HashSet(lista);
  setboth.addAll(listb);
  lista.clear();
  lista.addAll(setboth);
  </code></pre>