Split String at different lengths in Java

Question

I want to split a string after a certain length.

Let's say we have a string of "message"

123456789

Split like this :

"12" "34" "567" "89"

I thought of splitting them into 2 first using

"(?<=\\G.{2})"

Regexp and then join the last two and again split into 3 but is there any way to do it on a single go using RegExp. Please help me out

i dont know about regex for different length but you can do it using substring inside any loop. — Lalit Verma, Nov 29 '17 at 05:19
You need to say what is so *regular* about pattern you want to find, or delimiter you want to match. Without it we can't really help you use regex for your problem. — Pshemo, Nov 29 '17 at 05:41
@Pshemo It's like there are a lot of strings like the example above and I want to split them into 2,2,3,2 length and every string has exactly 9 numbers that's the pattern. — Srikar, Nov 29 '17 at 06:01
OK, so posted answers should do what you wanted. `split` is not the way here, use Matcher's `find()` method. — Pshemo, Nov 29 '17 at 06:05
Thank you for the help I'll give it a try and let you all know if there are any concerns. — Srikar, Nov 29 '17 at 06:08

Shafin Mahmud · Accepted Answer · 2017-11-29T10:37:29.990

Use ^(.{2})(.{2})(.{3})(.{2}).* (See it in action in regex101) to group the String to the specified length and grab the groups as separate Strings

  String input = "123456789";
  List<String> output = new ArrayList<>();

  Pattern pattern = Pattern.compile("^(.{2})(.{2})(.{3})(.{2}).*");
  Matcher matcher = pattern.matcher(input);

  if (matcher.matches()) {
     for (int i = 1; i <= matcher.groupCount(); i++) {
         output.add(matcher.group(i));
     }
  }

  System.out.println(output);

NOTE: Group capturing starts from 1 as the group 0 matches the whole String

And a Magnificent Sorcery from @YCF_L from comment

  String pattern = "^(.{2})(.{2})(.{3})(.{2}).*";
  String[] vals = "123456789".replaceAll(pattern, "$1-$2-$3-$4").split("-");

Whats the magic here is you can replace the captured group by replaceAll() method. Use $n (where n is a digit) to refer to captured subsequences. See this stackoverflow question for better explanation.

NOTE: here its assumed that no input string contains - in it. if so, then find any other character that will not be in any of your input strings so that it can be used as a delimiter.

yes. though I assumed that. But its better to mention. thanks. — Shafin Mahmud, Nov 29 '17 at 10:31

score 3 · Answer 2 · answered Nov 29 '17 at 05:48

3

test this regex in regex101 with 123456789 test string.

^(\d{2})(\d{2})(\d{3})(\d{2})$

output :

Match 1
Full match  0-9 `123456789`
Group 1.    0-2 `12`
Group 2.    2-4 `34`
Group 3.    4-7 `567`
Group 4.    7-9 `89`

answered Nov 29 '17 at 05:48

Mojtaba Yeganeh

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Split String at different lengths in Java

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