How can I split a string in Java and retain the delimiters?

Question

I have this string (Java 1.5):

:alpha;beta:gamma;delta

I need to get an array:

{":alpha", ";beta", ":gamma", ";delta"}

What is the most convenient way to do it in Java?

Answer 1

str.split("(?=[:;])")

This will give you the desired array, only with an empty first item. And:

str.split("(?=\\b[:;])")

This will give the array without the empty first item.

• The key here is the (?=X) which is a zero-width positive lookahead (non-capturing construct) (see regex pattern docs).
• [:;] means "either ; or :"
• \b is word-boundary - it's there in order not to consider the first : as delimiter (since it is the beginning of the sequence)

Answer 2

To keep the separators, you can use a StringTokenizer:

new StringTokenizer(":alpha;beta:gamma;delta", ":;", true)

That would yield the separators as tokens.

To have them as part of your tokens, you could use String#split with lookahead.