Split string to equal length substrings in Java

java regex string split
Emil picture Emil · Sep 21, 2010 · Viewed 156.6k times · Source

How to split the string "Thequickbrownfoxjumps" to substrings of equal size in Java. Eg. "Thequickbrownfoxjumps" of 4 equal size should give the output.

["Theq","uick","brow","nfox","jump","s"]

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Split string into equal-length substrings in Scala

Answer

Alan Moore picture Alan Moore · Sep 21, 2010

Here's the regex one-liner version:

System.out.println(Arrays.toString(
    "Thequickbrownfoxjumps".split("(?<=\\G.{4})")
));

\G is a zero-width assertion that matches the position where the previous match ended. If there was no previous match, it matches the beginning of the input, the same as \A. The enclosing lookbehind matches the position that's four characters along from the end of the last match.

Both lookbehind and \G are advanced regex features, not supported by all flavors. Furthermore, \G is not implemented consistently across the flavors that do support it. This trick will work (for example) in Java, Perl, .NET and JGSoft, but not in PHP (PCRE), Ruby 1.9+ or TextMate (both Oniguruma). JavaScript's /y (sticky flag) isn't as flexible as \G, and couldn't be used this way even if JS did support lookbehind.

I should mention that I don't necessarily recommend this solution if you have other options. The non-regex solutions in the other answers may be longer, but they're also self-documenting; this one's just about the opposite of that. ;)

Also, this doesn't work in Android, which doesn't support the use of \G in lookbehinds.

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