This tokenizer uses regex pattern matching to construct distinct tokens
for the input stream. It takes two arguments: "pattern" and "group".
- "pattern" is the regular expression.
- "group" says which group to extract into tokens.
group=-1 (the default) is equivalent to "split". In this case, the tokens will
be equivalent to the output from (without empty tokens):
String#split(java.lang.String)
Using group >= 0 selects the matching group as the token. For example, if you have:
pattern = \'([^\']+)\'
group = 0
input = aaa 'bbb' 'ccc'
the output will be two tokens: 'bbb' and 'ccc' (including the ' marks). With the same input
but using group=1, the output would be: bbb and ccc (no ' marks)
NOTE: This Tokenizer does not output tokens that are of zero length.