title: How do I check if a String contains the same letter more than once?
body: <p>I'm a bit confused in how I would check if a String contains the same letter more than once.</p>
  
  <pre><code>ArrayList&lt;String&gt; words = new ArrayList&lt;String&gt;();
  
  words.add("zebra");
  words.add("buzzer");
  words.add("zappaz");
  </code></pre>
  
  <p>Let's say I only want to print out any words which contain more than one "z", therefore only "buzzer" and "zappaz" would get printed. How would I do this?</p>