How can I change the date format in Java? [duplicate]

Answer 1

This is just Christopher Parker's answer adapted to use the new¹ classes from Java 8:

final DateTimeFormatter OLD_FORMATTER = DateTimeFormatter.ofPattern("dd/MM/yyyy");
final DateTimeFormatter NEW_FORMATTER = DateTimeFormatter.ofPattern("yyyy/MM/dd");

String oldString = "26/07/2017";
LocalDate date = LocalDate.parse(oldString, OLD_FORMATTER);
String newString = date.format(NEW_FORMATTER);

1 well, not that new anymore, Java 9 should be released soon.

Answer 2

Or you could go the regex route:

String date = "10/07/2010";
String newDate = date.replaceAll("(\\d+)/(\\d+)/(\\d+)", "$3/$2/$1");
System.out.println(newDate);

It works both ways too. Of course this won't actually validate your date and will also work for strings like "21432/32423/52352". You can use "(\\d{2})/(\\d{2})/(\\d{4}" to be more exact in the number of digits in each group, but it will only work from dd/MM/yyyy to yyyy/MM/dd and not the other way around anymore (and still accepts invalid numbers in there like 45). And if you give it something invalid like "blabla" it will just return the same thing back.

Answer 3

SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd");
sdf.format(new Date());

This should do the trick

Answer 4

How to convert from one date format to another using SimpleDateFormat:

final String OLD_FORMAT = "dd/MM/yyyy";
final String NEW_FORMAT = "yyyy/MM/dd";

// August 12, 2010
String oldDateString = "12/08/2010";
String newDateString;

SimpleDateFormat sdf = new SimpleDateFormat(OLD_FORMAT);
Date d = sdf.parse(oldDateString);
sdf.applyPattern(NEW_FORMAT);
newDateString = sdf.format(d);