Java, change date format.

Question

I want to change the format of date from yyyyMM to yyyy-MM.

I have found out that the two ways below works equally well. But which one is the best? I would prefer methodTwo since it is simplier, but is there any advantage using methodOne?

public String date;

public void methodOne()
{ 
    String newDate = date; 
    DateFormat formatter = new SimpleDateFormat("yyyyMM");
    DateFormat wantedFormat = new SimpleDateFormat("yyyy-MM");
    Date d = formatter.parse(newDate);
    newDate = wantedFormat.format(d);
    date = newDate;
}


public void methodTwo()
{
    date = date.substring(0, 4) + "-" + date.substring(4, 6);
}

The first one is more readable and I'd prefer it, if there are no other time / memory restrictions. Though, this question is opinion-based. — awesoon
– awesoon, Commented Feb 19, 2016 at 9:50

eztam · Accepted Answer · 2016-02-19 09:51:15Z

4

You should prefer method one because it can detect if the input date has an invalid format. Method two could lead to problems, when it's not guaranteed that the input date is always in the same format. Method one is also more easy to adjust, when you later want to change either the input or the output format.

It could make sense to use method two if performance really matters, because it should be slightly faster than method one.

answered Feb 19, 2016 at 9:51

eztam

3,8737 gold badges40 silver badges58 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user2939293 Over a year ago

Thank you, that was the kind of answer I was looking for. I accepted your answer since you were the first to answer.

randombee · Accepted Answer · 2016-02-19 09:53:33Z

3

I would say that methodOne is much more generic. If you need to change your wanted format again, you only have to change the argument "yyyy-MM" for whatever new format you want, no matter how exotic it is. I found that when you work with people all across the world, methodOne is much more useful and also easier to read than using substrings. Using substrings means that you have no way to make sure that what is coming has the format you expect. You could be splitting in the wrong order.

answered Feb 19, 2016 at 9:53

randombee

7191 gold badge8 silver badges26 bronze badges

Comments

Santosh Jadi · Accepted Answer · 2016-02-19 10:17:47Z

1

Get it in a Easy Way:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
String date = sdf.format(yourDate);

answered Feb 19, 2016 at 10:17

Santosh Jadi

1,5357 gold badges32 silver badges61 bronze badges

Comments

White Bullet · Accepted Answer · 2016-02-19 11:23:28Z

1

Using the SimpleDateFormat is the industry standard. It is easier to read and maintain in the future as it allows the format to be changed with ease.

answered Feb 19, 2016 at 11:23

White Bullet

2254 silver badges11 bronze badges

Comments

Basil Bourque · Accepted Answer · 2016-02-23 10:30:33Z

`java.time.YearMonth`

There is a third way: Use the YearMonth class built into Java 8 and later as part of the java.time framework.

You don't have a date and a time, so using a date-time class such as java.util.Date or even the java.time types (Instant, OffsetDateTime, ZonedDateTime) is not a good fit. As you have only a year and a month use, well, YearMonth – a perfect fit.

Rather than pass Strings around your code, pass these YearMonth values. Then you get type-safety and valid values.

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuuyy");
YearMonth ym = YearMonth.parse( input );

The default format used by the YearMonth::toString method uses the standard ISO 8601 format you desire.

String output = ym.toString();

Collectives™ on Stack Overflow

Java, change date format.

5 Answers 5

1 Comment

Comments

Comments

Comments

`java.time.YearMonth`

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

Comments

Comments

Comments

java.time.YearMonth

Comments

Your Answer

Sign up or log in

Post as a guest

Related

`java.time.YearMonth`