extract all substring combinations between 2 characters using regex

Question

I got a String s = "HFGFHFFHSSH". What I want as output is every possible substring combination between 'H'

The output of the above String should be HFGFH HFFH HSSH

I tried the following:

String s = "HFGFHFFHSSH";  
Pattern pattern = Pattern.compile("H(.*?)H");
Matcher matcher = pattern.matcher(s);
while (matcher.find()){
  System.out.println(matcher.group(0));
}

Unfortunalety the output is missing one substring resulting in HFGFH HSSH

See also http://stackoverflow.com/questions/17971466/java-regex-overlapping-matches — Wiktor Stribiżew, Dec 09 '16 at 17:42
@WiktorStribiżew oh thanks I didn't come across that question in my search. — motaa, Dec 09 '16 at 17:47

score 2 · Accepted Answer · answered Dec 09 '16 at 17:42

You should be using a lookahead regex for this and capture the value from inside the lookahead:

(?=(H[^H]*H))

(?=...) is positive lookahead that asserts presence of text surrounded by H on either side
(...) inside the lookahead is for capturing the matched value in group #1

RegEx Demo

Code:

String s = "HFGFHFFHSSH";  
final Pattern pattern = Pattern.compile("(?=(H[^H]*H))");
Matcher matcher = pattern.matcher(s);

while (matcher.find()) {
   System.out.println(matcher.group(1));
}

The regex101 site enlightens me what really is going on in the regex stuff. :) — motaa, Dec 09 '16 at 18:24

extract all substring combinations between 2 characters using regex

1 Answers1