RegEx in java, non-capturing group

Question

Let's say I have code below:

Pattern pt = Pattern.compile("(?:h)?o");
Matcher m = pt.matcher("hours 123");
m.find();
System.out.println(m.group(0));

And the result is

ho

Here in regex I have a non-capturing group (?:h). Why is this group included in the final results? I just want to get "o" instead.

fyi, a non-capturing group is still part of the whole match, it is just not included in the group matches. — OGHaza
– OGHaza, Commented Nov 20, 2013 at 10:39
finally i get it. (?:h) is included in result.it just indicates that i can not use $1, it is made for performance reasons. — Oleksandr Papchenko
– Oleksandr Papchenko, Commented Nov 20, 2013 at 12:20

Martijn Courteaux · Accepted Answer · 2013-11-20 09:59:31Z

2

Your positive lookbehind is wrong. It should be this:

(?<=h)o

answered Nov 20, 2013 at 9:59

Martijn Courteaux

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1 Comment

That is, if the OP wanted to do a lookbehind. Nothing in the OP's question indicates that the OP wanted to do so.

rzymek · Accepted Answer · 2013-11-20 09:59:36Z

2

group(0) is the whole match. You need to

Pattern.compile("(?:h)?(o)");

and use m.group(1)

answered Nov 20, 2013 at 9:59

rzymek

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This is the actual answer to the OP's question, even if the other answer was OP's preferred solution.