Retrieve all instances of a regex pattern

Question

I have this string (example):

"St 28828 En, St 217n En, St 38729mdnj dnj]spw En"

If I run this code...

Pattern patt = Pattern.compile("St(?s)(.*)En");
Matcher matc = patt.matcher(vartext);
boolean found = false;
while (matc.find()) {
    found = true;
    Log.d("LogCalc", matc.group());
} 
if (!found) {
    Log.d("LogCalc", "Nothing");
}

I get the entire string, I assume because the very first string starts at St & the very last ends at En. How can I get each individual iteration: 28828, 217n, 38729mdnj dnj]spw? I assume there is a way to have the regex pattern start from the beginning.

Thanks,

Thanks @Pshemo, with <.*?> I'm able to resolve the string covering from start to end. Can regex do the iteration as well? Or I might need to use replacement options to get them? — Felipe Vidal, Jun 28 '23 at 18:03
"Can regex do the iteration as well?" I am not sure what you mean since you are already iterating over all matches in your code via `while (matc.find()){ ... matc.group().. }`? — Pshemo, Jun 28 '23 at 18:07
It resolves partially, as "?" helped with ensuring I don't get the entire string from beginning to end, but only the first iteration. Right now I'm missing to know if regex can repeat the process & retrieve each individual instance by itself, or I need to iterate with a while or so. — Felipe Vidal, Jun 28 '23 at 18:09
"*`found = true` was breaking the iteration*" that shouldn't be happening in your example since loop condition is based only on `matc.find()`. Also there is no `break` nor `return` based on `found`. I am guessing that you ware talking about your *real* code, not the one posted here. Anyway congrats for finding that problem, and good luck with your code :) — Pshemo, Jun 28 '23 at 18:28

score 0 · Answer 1 · answered Jun 28 '23 at 18:32

"... I get the entire string, I assume because the very first string starts at St & the very last ends at En. ..."

With Matcher#group, if no argument is specified, it will return the value of the entire match—not just the capturing group.
The problem with the pattern is that it should be using a lazy-quantifier, ?.

This will match the first encountered En, as opposed to the last.

St(?s)(.*?)En

From here, to return the value of the captured group, provide the number as a value.
Group numbers start at 1—a 0 will return the entire match, similar to what you currently have.

Matcher#group (Java SE 20 & JDK 20).

matc.group(1)

Retrieve all instances of a regex pattern

1 Answers1