title: Why wasn't Joda Interval made comparable?
body: <p>I've been attempting to generate a <code>TreeMap&lt;Interval, Set&lt;Object&gt;&gt;</code> for storing person entities in age-grouped sets where the <code>Interval</code> describes the boundary of the age group. I got the following error when I attempted to do this.</p>
  
  <pre><code>java.lang.ClassCastException: org.joda.time.Interval cannot be cast to java.lang.Comparable
  </code></pre>
  
  <p>Swapping <code>Interval</code> for a <code>DateTime</code> works perfectly, but the map's key then must be used as input to create an <code>Interval</code>.</p>
  
  <p>Why wasn't Joda <code>Interval</code> made comparable?</p>