title: Can't send a Month as a parameter
body: <p>I'm using <code>jFreeChart</code> to make a Gantt Chart and for adding each task im using <code>Enumeration</code> utility for gets elements from an <code>Hashtable</code>. I can send the year and the day, but get an Exception when a try to send Month like a parameter with this line:</p>
  
  <pre><code>hT.get(obj).getFechaFin().getMonth()
  </code></pre>
  
  <p>Wherein <code>hT</code> is an <code>Hashtable</code> and <code>obj</code> is an index. I understand that <code>getMonth()</code> returns an <code>int</code>. It throws:</p>
  
  <pre><code>Exception in thread "AWT-EventQueue-0" 
      java.lang.IllegalArgumentException: Requires start &lt;= end.
  </code></pre>
  
  <p>Then changed that code line for <code>Calendar.MARCH</code> it worked and generated the chart. And it also returns a <code>int</code>, their indexes begins both with 0 being January the first month. So why isn't working? I'm using <code>jCalendar-1.4.jar</code> to easily get dates from a component.</p>
  
  <pre><code>//here I load the Hashtable and I generate the Chart
  
  public static IntervalCategoryDataset createDataset(){
      final TaskSeries s1 = new TaskSeries("Scheduled");
  
      for (Enumeration e = hT.keys(); e.hasMoreElements();) {
          Object obj = e.nextElement();
          s1.add(new Task(hT.get(obj).getTarea().toString(),
              new SimpleTimePeriod(
                  date(hT.get(obj).getFechaInicio().getDay(),
                       hT.get(obj).getFechaInicio().getMonth(),                                              
                       hT.get(obj).getFechaInicio().getYear()),
                  date(hT.get(obj).getFechaFin().getDay(),
                       hT.get(obj).getFechaFin().getMonth(),                                              
                       hT.get(obj).getFechaFin().getYear()))));
      }
  
      final TaskSeriesCollection collection = new TaskSeriesCollection();
      collection.add(s1);
      return collection;
  }
  
  //and here receives the month parameter 
  private static Date date(final int day, final int month, final int year){
       final Calendar calendar = Calendar.getInstance();
       calendar.set(year,month,day);
       final Date result = calendar.getTime();
       return result;
  }
  </code></pre>
  
  <p>I need to use <code>hT.get(obj).getFechaFin().getMonth()</code> 'cause it is saved in a binary file. Is there a way to convert to <code>Calender.MONTH</code> format?</p>