Java RegEx: Extract multiple sub-strings from a string

Question

I want to extract all sub-strings from a string that are enclosed in certain tags. For example, if I have an input string that encloses some sub-strings in "*" tags:

I contain two terms to extract: *first term* and *second term*

What I want to get is the two sub-strings "first term" and "second term". I tried with the following code:

List<String> matches = new ArrayList<>();
Matcher m = Pattern.compile(".*\\*(.*)\\*.*").matcher(inputString);
while(m.find()){
   matches.add(m.group(1));
}

But this gives me incorrect results. I read the API doc about the group method, but to be honest I don't quite understand what it means and how it works. I'd be thankful if someone could tell me what the best approach is to gather all wanted sub-strings here.

Thanks!

"Greedy" means that if there is more than one way to get a match, it will choose the match with the largest number of characters. If your regex is a.*b, and your input string is a1111b...a2222b, this will match the entire string, since it chooses the largest possible match for .*. By adding a question mark, a.*?b, you tell it to choose the match with the smallest number of characters. So this would match a1111b. — ajb
– ajb, Commented Sep 12, 2016 at 1:39

Andrew Sklyarevsky · Accepted Answer · 2016-09-11 22:41:13Z

1

Try the following expression:

\\*([^\\*]+)\\*

The needed substring will be in the first group.

answered Sep 11, 2016 at 22:41

Andrew Sklyarevsky

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3 Comments

Andreas Over a year ago

You don't need to escape * inside a character class. \\*([^*]+)\\* or [*]([^*]+)[*] will do.

user3237736 Over a year ago

great, thanks you guys! but I don't quite understand: what exactly is the difference now to my approach? It seems it's the usage of the squared brackets, but I don't understand why it's neccessary?

Andrew Sklyarevsky Over a year ago

Square brackets allow matching anything but not an asterisk, because an asterisk ends the phrase you want to match. For more information on regular expressions, see for example this article at WikiBooks: en.wikibooks.org/wiki/Regular_Expressions/… and StackOverflow Documentation: stackoverflow.com/documentation/regex/topics .

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