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Hi

I have a string, for example:

String str = "aaab";

I would like to use the matches() method of the String class to test the
string's first 3 characters are identical.
I would like to do this in a general way by using regular expressions.

Tried (but doesn't work):

if (str.matches("xxx[a-zA-Z]"))
return true;

According to the regular expression, x is suppose to be a character.
Not sure, why this is not working, or if it's even possible to do it using
the matches method.
Any help appreciated.

Cheers
Sharp

Sharp wrote:
> I would like to use the matches() method of the String class to test the
> string's first 3 characters are identical.

> Tried (but doesn't work):
>
> if (str.matches("xxx[a-zA-Z]"))
> return true;
>
> According to the regular expression, x is suppose to be a character.

Here, x is a character, that is 'x'. To achieve what you want you would
need something like "((.)\\2\\2).*". But using regexes is not the right
answer to this problem. It is better to write a method that just checks
that the first three characters are the same. It's just a couple of
lines of code, probably faster than using a regex too.

--
Daniel Sjöblom
Remove _NOSPAM to reply by mail

> Sharp wrote:
> > I would like to use the matches() method of the String class to test the
> > string's first 3 characters are identical.
>
> > Tried (but doesn't work):
> >
> > if (str.matches("xxx[a-zA-Z]"))
> > return true;
> >
> > According to the regular expression, x is suppose to be a character.
>
> Here, x is a character, that is 'x'. To achieve what you want you would
> need something like "((.)\\2\\2).*". But using regexes is not the right
> answer to this problem. It is better to write a method that just checks
> that the first three characters are the same. It's just a couple of
> lines of code, probably faster than using a regex too.

Thanks for your help.
Your suggested regular expression works, but I dont fully understand it.
I assume that '\\2' means same as the previous character, which is '.'
Not sure what the '*' means.
Could you shed some light on the whole thing?

Cheers
Sharp

Sharp wrote:

>>Sharp wrote:
>>
>>
>>>I would like to use the matches() method of the String class to test the
>>>string's first 3 characters are identical.
>>>
>>>
>>>Tried (but doesn't work):
>>>
>>>if (str.matches("xxx[a-zA-Z]"))
>>> return true;
>>>
>>>According to the regular expression, x is suppose to be a character.
>>>
>>>
>>Here, x is a character, that is 'x'. To achieve what you want you would
>>need something like "((.)\\2\\2).*". But using regexes is not the right
>>answer to this problem. It is better to write a method that just checks
>>that the first three characters are the same. It's just a couple of
>>lines of code, probably faster than using a regex too.
>>
>>
>
>Thanks for your help.
>Your suggested regular expression works, but I dont fully understand it.
>I assume that '\\2' means same as the previous character, which is '.'
>Not sure what the '*' means.
>Could you shed some light on the whole thing?
>
>Cheers
>Sharp
>
>
\\2 is \2 which means capturing group 2.
* means zero or more.
Read the javadoc for Pattern class.

Am Mon, 02 May 2005 11:16:57 GMT schrieb Sharp:

> Could you shed some light on the whole thing?

http://www.amk.ca/python/howto/regex/

Christian

"hiwa" <> wrote in message
news:d553k2$8k2$...
> Sharp wrote:
>
> >>Sharp wrote:
> >>
> >>
> >>>I would like to use the matches() method of the String class to test
the
> >>>string's first 3 characters are identical.
> >>>
> >>>
> >>>Tried (but doesn't work):
> >>>
> >>>if (str.matches("xxx[a-zA-Z]"))
> >>> return true;
> >>>
> >>>According to the regular expression, x is suppose to be a character.
> >>>
> >>>
> >>Here, x is a character, that is 'x'. To achieve what you want you would
> >>need something like "((.)\\2\\2).*". But using regexes is not the right
> >>answer to this problem. It is better to write a method that just checks
> >>that the first three characters are the same. It's just a couple of
> >>lines of code, probably faster than using a regex too.
> >>
> >>
> >
> >Thanks for your help.
> >Your suggested regular expression works, but I dont fully understand it.
> >I assume that '\\2' means same as the previous character, which is '.'
> >Not sure what the '*' means.
> >Could you shed some light on the whole thing?
> >
> >Cheers
> >Sharp
> >
> >
> \\2 is \2 which means capturing group 2.
> * means zero or more.
> Read the javadoc for Pattern class.

Thanks!

Cheers
Sharp