Returning the String found with a regular expression

Question

If I have a regular expression, how do I return the substring that it has found? I'm sure I must be missing something obvious, but I've found various methods to confirm that that substring is contained in the string I'm searching, or to replace it with something else, but not to return what I've found.

Answer 1

Matcher matcher = Pattern.compile("a+").matcher("bbbbaaaaabbbb");
if(matcher.find())
     System.out.println(matcher.group(0)); //aaaaa

If you want specific parts

Matcher matcher = Pattern.compile("(a+)b*(c+)").matcher("bbbbaaaaabbbbccccbbb");
if(matcher.find()){
   System.out.println(matcher.group(1)); //aaaaa
   System.out.println(matcher.group(2)); //cccc
   System.out.println(matcher.group(0)); //aaaaabbbbcccc 
}

Group 0 is the complete pattern.. other groups are separated with parenthesis in the regex (a+)b*(c+) and can be get individually