TestBiFunction.java

public class TestBiFunction {

  public static void main(String ... args){
    //don't want to resolve dates in constructor -> compile error
    List<GroovyReportTask> reportTasks = ReportUtils.splitInterval(firstDay, today,
      (dtStart, dtEnd) -> new GroovyReportTask(getScriptFile(), null, dtStart, dtEnd));
  }
  
  public static <T extends ReportTask> List<T> splitInterval(Date startDay, Date endDayExclusive, int interval, BiFunction<Date, Date, T> builderForDay) {
    Date startOfEndDay = DateUtil.startOfGMTDay(endDayExclusive);
    List<T> res = Lists.newArrayList();
    Date startTask = DateUtil.startOfGMTDay(startDay);
    Date endTask = DateUtils.addDays(startTask, interval);
    while (endTask.before(startOfEndDay)) {
      res.add(builderForDay.apply(startTask, endTask));
      startTask = DateUtils.addDays(startTask, interval);
      endTask = DateUtils.addDays(startTask, interval);
    }
    return res;
  }
}