title: Joda-Time: what's the difference between Period, Interval and Duration?
body: <p>In <a href="http://www.joda.org/joda-time/" rel="noreferrer">Joda-Time</a> 2, what is the difference between the three kinds of time spans: </p>
  
  <ul>
  <li><a href="http://www.joda.org/joda-time/apidocs/org/joda/time/Period.html" rel="noreferrer">Period</a></li>
  <li><a href="http://www.joda.org/joda-time/apidocs/org/joda/time/Interval.html" rel="noreferrer">Interval</a></li>
  <li><p><a href="http://www.joda.org/joda-time/apidocs/org/joda/time/Duration.html" rel="noreferrer">Duration</a></p>
  
  <ol>
  <li><p>Why do we need three classes?</p></li>
  <li><p>Which one performs better? </p></li>
  <li><p>Why is <em>dividing</em> a Period or Duration or Interval instance not implemented? E.g. <code>p = p.divideBy(2);</code></p></li>
  </ol></li>
  </ul>