Question

I’m new to regular expressions and java so please bear with my newbish question.

I want to do the following:

If I have a string:

"I like ice cream only if it is chocolate ice cream. Chocolate cream" 

and a pattern like

"chocolate ice cream" 

I want to match and replace all words matched with a # surrounding them. Like this:

"I like #ice cream# only if it is #chocolate ice cream#. #Cholcolate cream#"

I used java’s regex api and I understand I can use Matcher.replaceAll. But I’m having trouble coming up with a proper regex. I came up with this chocolate*\\s*ice*\\s*cream*. But the problem here is it’s only matching the whole substring, i.e "chocolate ice cream". I think something like this could work:

chocolate|ice|cream|chocolate ice|ice cream|chocolate cream|chocolate ice cream

etc, i.e all permutations, but this would be cumbersome as the substring grows.

I would appreciate any ideas on proceeding in the right direction.

Answer 1

Use the pattern:

(?i)\b((?:chocolate|ice|cream)(?:\s+(?:chocolate|ice|cream))*)\b

and replace it with:

#$1#

Demo:

String s = "I like ice cream only if it is chocolate ice cream. Chocolate cream";
s = s.replaceAll("(?i)\\b((?:chocolate|ice|cream)(?:\\s+(?:chocolate|ice|cream))*)\\b", "#$1#");
System.out.println(s);

The word boundaries cause “creamy” (and other such words) not to be replaced.

Note that this will change "ice ice" into "#ice ice#" (ie. the words can occur more than once!), as @stema mentioned in the comments.