You can try this to avoid indicating custom date and if there is need to display start and end dates of current month:
LocalDate start = LocalDate.now().minusDays(LocalDate.now().getDayOfMonth()-1);
LocalDate end = LocalDate.now().minusDays(LocalDate.now().getDayOfMonth()).plusMonths(1);
System.out.println("Start of month: " + start);
System.out.println("End of month: " + end);
Result:
> Start of month: 2019-12-01
> End of month: 2019-12-30