java.time
Here’s the modern answer.
DateTimeFormatter sourceFormatter = DateTimeFormatter.ofPattern("dd/MM/uuuu");
DateTimeFormatter displayFormatter = DateTimeFormatter
.ofLocalizedDate(FormatStyle.SHORT)
.withLocale(Locale.forLanguageTag("zh-SG"));
String dateString = "31/05/2011";
LocalDate date = LocalDate.parse(dateString, sourceFormatter);
System.out.println(date.format(displayFormatter));
Output from this snippet is:
31/05/11
See if you can live with the 2-digit year. Or use FormatStyle.MEDIUM to obtain 2011年5月31日. I recommend you use Java’s built-in date and time formats when you can. It’s easier and lends itself very well to internationalization.
If you need the exact format you gave, just use the source formatter as display formatter too:
System.out.println(date.format(sourceFormatter));
31/05/2011
I recommend you don’t use SimpleDateFormat. It’s notoriously troublesome and long outdated. Instead I use java.time, the modern Java date and time API.
To obtain a specific format you need to format the parsed date back into a string. Netiher an old-fashioned Date nor a modern LocalDatecan have a format in it.
Link: Oracle tutorial: Date Time explaining how to use java.time.