What's the difference between these two below?

Question

System.out.println(matcher.group(1));
System.out.println(matcher.group());

I like to know what's the difference between the above two codes. I get different outputs. Can anybody elaborate on this?

Thanks

Answer 1

I point you to the JavaDocs for Matcher

group():

Returns the input subsequence matched by the previous match

group(int):

Returns the input subsequence captured by the given group during the previous match operation.

Answer 2

The API doc is a very good place to look first.

Answer 3

The call to group() gives you the entire string that matched, whereas group(1) gives you the first parenthesized "Capturing" group (or more generally, group(n) will give you the n'th capturing group, counting left/opening parenthesis, starting from 1).

So for example, if you had an input string like this:

The quick brown fox

And you matched against the following regular expression (without the quotes):

"The (\\w+)"

Then group() would give you "The quick" and group(1) would give you "quick".

For more details on how all of this regular expression stuff works in Java, look See the java.util.regex.Matcher JavaDoc.