Regex

Hi All

Could any one let me know how quantifier actually works?

When i tried to search using pattern "a.c" in "abc 34 a cac", i got the expected output i.e
0 abc
7 a c
So, Metacharacter . is working here.

but if i use some quantifiers like "a.c*" or "a.c?", then output is coming something like this
0 abc
7 a c
10 ac

Here even ac is coming in output, what happened to metacharacter here?

Could anyone explain how metacharacter and quantifiers are working here?

Thanks
Krishan

The dot matches the "c". Both "?" and "*" mean that the character they follow can be missing, so they match no characters.

Hi Ulf

do you mean to say that metacharacters do not matter when using quantifiers?

It's not that the metacharacter doesn't matter at all. But if the quantifier can be zero, then the pattern can match zero occurrences of the metacharacter. So there are at least some possible matches where the metacharacter does not occur at all.

Try using + instead of * - you will see that + means at least one occurrence of the preceding character. So it will not give you this behavior of "ignoring" that character.
[ May 13, 2008: Message edited by: Jim Yingst ]

Hi Jim

Thanks for your reply.

When you use quantifiers, does it account for all the characters preceding it or the immediate one? Do we have any option regarding this?

If i use seach pattern as a.*c in place of a.c*, it works like a greedy quantifier. Could any one tell me what's the difference between above two pattern?

Thanks
Krishan

Have you been through the Java Tutorials? It explains quantifiers there.

a.* --> means a followed by any character zero or more times
a.c* --> means a followed by any one character followed by character c zero or more times

also look at +, ?

check here --> http://java.sun.com/docs/books/tutorial/essential/regex/quant.html

Hi

It solved most of my problem but i still have one doubt:

If a.c* means a followed by any one character followed by character c zero or more times why does it ignores 34 in "abc 34 a cac" ?
Please help.

Thanks
Krishan

I don't understand your question - there's no "a" in "34", so why do you think it should match it?