Finding all of the matching substrings, not only the "most extended" one

Question

The code

String s = "y z a a a b c c z";
Pattern p = Pattern.compile("(a )+(b )+(c *)c");
Matcher m = p.matcher(s);
while (m.find()) {
    System.out.println(m.group());
}

prints

a a a b c c

which is right.

But logically, the substrings

a a a b c
a a b c c
a a b c
a b c c
a b c

match the regex too.

So, how can I make the code find those substrings too, i.e. not only the most extended one, but also its children?

Answer 1

You can use the reluctant qualifiers such as *? and +?. These match as little as possible, in contrast to the standard * and + which are greedy, i.e. match as much as possible. Still, this only allows you to find particular "sub-matches", not all of them. Some more control can be achieved using lookahead controlling non-capturing groups, also described in the docs. But in order to really find all sub-matches, you would probably have to do stuff yourself, i.e. build the automaton to which the regex corresponds and navigate it using custom code.

Answer 2

You will need a lazy quantifier.

Please try the following:

Pattern p = Pattern.compile("(a )+(b )+((c )*?)c");

Please also notice, that I grouped "c" once again, since I think that's what you want. Otherwise you would find arbitrarily many spaces, but not "c".