I have a function below which has an input Date and it will return the first and last Date of the next month in MM/dd/yyyy format.

String string = "01/01/2022";
DateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
Date dt = sdf .parse(string);
Calendar c = Calendar.getInstance();
c.setTime(dt);
c.add(Calendar.MONTH, 1);  
String firstDate = sdf.format(c.getTime());
System.out.println("FirstDate:"   firstDate);
c.add(Calendar.MONTH, 1);
c.add(Calendar.DAY_OF_MONTH, -1);
String lastDate = sdf.format(c.getTime());
System.out.println("LastDate:"   lastDate);

The above will give me an output like below

FirstDate:02/01/2022
LastDate:02/28/2022

This works well if the input is the first day of the previous month, what i would like to achieve is to get the FirstDate and LastDate of the next month even if the input is a date which is not the first date of the month for example 01/31/2022 gives me the output below

FirstDate:02/28/2022
LastDate:03/27/2022

But i would still like it to give me the first out of

FirstDate:02/01/2022
LastDate:02/28/2022

CodePudding user response：

Don't use Date as it is obsolete and buggy. Use LocalDate and other classes from the java.time package.

• the following takes an existing date first, adds 1 to the month. This will also cause the year to increase if required.
• then the dayOfMonth as either 1 or the last day of the month. Leap years are automatically considered.

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("MM/dd/yyyy");
LocalDate date = LocalDate.parse("12/22/2020", dtf);
date = date.plusMonths(1);
LocalDate endDate = date.withDayOfMonth(date.lengthOfMonth());
LocalDate startDate = date.withDayOfMonth(1);
System.out.println("FirstDate: "  startDate.format(dtf));
System.out.println("LastDate:  "  endDate.format(dtf));

prints

FirstDate: 01/01/2021
LastDate:  01/31/2021

CodePudding user response：

You can have that easier in Java 8. Use a java.time.YearMonth, get the current one with its method now() and derive the first and last LocalDate of it:

public static void main(String[] args) {
    // get the current month
    YearMonth currentMonth = YearMonth.now();
    // get the date with day of month = 1 using the current month
    LocalDate firstOfMonth = currentMonth.atDay(1);
    // then get its last date (no number required here)
    LocalDate lastOfMonth = currentMonth.atEndOfMonth();
    // prepare a formatter for your desired output (default: uuuu-MM-dd)
    DateTimeFormatter customDtf = DateTimeFormatter.ofPattern("MM/dd/uuuu");
    // print the month and year without a formatter (just for visualization)
    System.out.println("Month:     "   currentMonth);
    // then print both desired dates using the custom formatter
    System.out.println("FirstDate: "   firstOfMonth.format(customDtf));
    System.out.println("LastDate:  "   lastOfMonth.format(customDtf));
}

This prints

Month:     2022-05
FirstDate: 05/01/2022
LastDate:  05/31/2022

You can – of course – use any given month, there is YearMonth.of(int year, int month) which you could use in order to create your example value:

YearMonth currentMonth = YearMonth.of(2022, 2);