title: Would like to avoid duplicate entries in a ArrayList
body: <p>I am looking for an object like ArrayList that would let me avoid duplicate entries.
  For example it might have a method that calls 'contains()' to valid each entry before it is added to the ArrayList.</p>
  
  <pre><code>ArrayList&lt;String&gt; al = new ArrayList&lt;String&gt;();
  if(!al.contains("red")){
    al.add("red");
  }
  </code></pre>
  
  <p>Does something like this exist?</p>