Java regex - split string with leading special characters

Question

I am trying to split a string that contains whitespaces and special characters. The string starts with special characters. When I run the code, the first array element is an empty string.

String s = ",hm  ..To?day,.. is not T,uesday.";
String[] sArr = s.split("[^a-zA-Z]+\\s*");

Expected result is ["hm", "To", "day", "is", "not", "T", "uesday"]

Can someone explain how this is happening?

Actual result is ["", "hm", "To", "day", "is", "not", "T", "uesday"]

There is a leading , in your input. The string is split on it the first time into "" and the rest. — user11044402
– user11044402, Commented Jul 9, 2019 at 19:52
How can I update my regex to prevent the empty element being added? My goal is to add all words to array excluding any special characters and whitespaces. — coffeefirst
– coffeefirst, Commented Jul 9, 2019 at 20:01

Bohemian · Accepted Answer · 2019-07-09 20:17:17Z

2

Split is behaving as expected by splitting off a zero-length string at the start before the first comma.

To fix, first remove all splitting chars from the start:

String[] sArr = s.replaceAll("^([^a-zA-Z]*\\s*)*", "").split("[^a-zA-Z]+\\s*");

Note that I’ve altered the removal regex to trim any sequence of spaces and non-letters from the front.

You don’t need to remove from the tail because split discards empty trailing elements from the result.

edited Jul 9, 2019 at 20:17

answered Jul 9, 2019 at 20:11

Bohemian♦

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1 Comment

coffeefirst Over a year ago

Thanks. I accepted this answer because it shows me how to trim the beginning spaces/non-letters occurring 0 or more times.

MonkeyZeus · Accepted Answer · 2019-07-09 20:06:18Z

1

I would simplify it by making it a two-step process rather than trying to achieve a pure regex split() operation:

s.replaceAll( '[^a-zA-Z]+', ' ' ).trim().split( ' ' )

answered Jul 9, 2019 at 20:06

MonkeyZeus

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3 Comments

coffeefirst Over a year ago

Thanks for your response. I am still wondering why my regex didn't work and ended up adding the empty string. Can you explain?

user21926 Over a year ago

Your regex is working fine. Because the first character of your string matches your regex, it is returning a the empty string as the first element. You can think of it like this: there is a 0-length string before the first , in your subject string.

MonkeyZeus Over a year ago

@coffeefirst The first comma was matched by the regex provided to split() is the simplest explanation I can provide.

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