replace char in specific pattern or after specific character

Question

The task at hand is to replace "-" with "/" in a birthday format e.g. 03-12-89 -> 03/12/89. However, the "-" must be able to appear elsewhere in the string e.g. "My-birthday-is-on-the: 03/12/89".

I have tried creating substrings, replace the "-" in the birthday part and then combine the strings again. However, that solution is inflexible and fails the testcases.

I'm thinking I must be able to do this with a regular expression, although I seem unable to construct it. So now I'm back to: String newStr = input.replace("-", "/"); Which remove all instances of "-" which I don't want.

Can anyone help?

Use a regular expression to find the birthday, then only replace the characters within that match range — MadProgrammer
– MadProgrammer, Commented Jun 14, 2018 at 5:50
You can parse dates to find they are dates, and then apply regex only to them — Sid
– Sid, Commented Jun 14, 2018 at 5:51

Allan · Accepted Answer · 2018-06-14 05:55:18Z

3

You can use the following regex:

(?<=\d{2})-

with replacement \/ (no need to escape it in Java)

INPUT:

My-birthday-is-on-the: 03-12-89

OUTPUT:

My-birthday-is-on-the: 03/12/89

demo

Code:

String input = "My-birthday-is-on-the: 03-12-89";
System.out.println(input.replaceAll("(?<=\\d{2})-", "/"));

OUTPUT:

My-birthday-is-on-the: 03/12/89

edited Jun 14, 2018 at 5:55

answered Jun 14, 2018 at 5:52

Allan

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3 Comments

Allan Over a year ago

@TimBiegeleisen: You are right for the escape part thanks ;-)

Kenneth Over a year ago

It works the way you made it, but inside my method it doesn't? Any idea why? ´private static String changeFormat(String input) { String newStr = input.replace("(?<=\\d{2})-", "/"); return newStr; }´ newStr is the same as the input string

Allan Over a year ago

@Kenneth: this is normal the method should be replaceAll and not replace as described in my answer

Tim Biegeleisen · Accepted Answer · 2018-06-14 06:19:11Z

2

The easiest way which comes to mind is just match \d{2}-\d{2}-\d{2}, with capture groups. Then, use those captured numbers to rebuild the birthdate the way you want it. Something like this:

String input = "My-birthday-is-on-the: 03/12/89";
input = input.replaceAll("\\b(\\d{2})-(\\d{2})-(\\d{2})\\b", "$1/$2/$3");

Demo

The advantage of specifying the full pattern is that it avoids the chance of matching anything other than a 6 digit dash-separated birthday.

Edit:

Based on your comment below, it sounds like maybe you want to do this replacement on a two dash separated number, with any number of digits. In this case, we can slightly modify the above code to the following:

String input = "Your policy number is: 123-45-6789.";
input = input.replaceAll("\\b(\\d+)-(\\d+)-(\\d+)\\b", "$1/$2/$3");

edited Jun 14, 2018 at 6:19

answered Jun 14, 2018 at 5:53

Tim Biegeleisen

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4 Comments

Kenneth Over a year ago

Inside the my method: private static String changeFormat(String input) { String newStr = input.replaceAll("\\b(\\d{2})-(\\d{2})-(\\d{2})\\b", "$1/$2/$3"); return newStr; } The output is still the same as the input. I don't get it (i have accounted for the wrong input in your example.)

Tim Biegeleisen Over a year ago

@Kenneth I don't know your code. Try to start with my demo, or the other answer, and go from there.

Kenneth Over a year ago

Code is simple: call this method: System.out.println(changeFormat("Your policy number is: 123-45-6789.")); With the above implementation

Kenneth Over a year ago

I love you :) Thank you SO much. Code works. I'll analyse to see why and learn something from it.

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