title: Difference between Calendar.HOUR and Calendar.HOUR_OF_DAY?
body: <p>What is the difference between <code>Calendar.HOUR</code> and <code>Calendar.HOUR_OF_DAY</code> ?
  When to use <code>Calendar.HOUR</code> and <code>Calendar.HOUR_OF_DAY</code> ?
  I am confused sometime <code>Calendar.HOUR</code> this works fine and othertime <code>Calendar.HOUR_OF_DAY</code> this works fine. What they return in the form of int? 
  I have read <a href="http://developer.android.com/reference/java/util/Calendar.html">this</a> documentation but not understood the difference.
  Any suggestions
  Thanks.</p>