Java: validating a certain string pattern

Question

I am trying to validate a string in a 'iterative way' and all my tryouts just fail! I find it a bit complicated and i'm guessing maybe you could teach me how to do it right. I assume that most of you will suggest me to use regex patterns but i dont really know how, and in general, how can a regex be defined for infinite "sets"?

The string i want to validate is "ANYTHING|NUMBER_ONLY,ANYTHING|NUMBER_ONLY..."

for example: "hello|5,word|10" and "hello|5,word|10," are both valid.

note: I dont mind if the string ends with or without a comma ','.

Eser Aygün · Accepted Answer · 2012-04-17 07:31:17Z

1

Kleene star (*) lets you define "infinite sets" in regular expressions. Following pattern should do the trick:

[^,|]+\|\d+(,[^,|]+\|\d+)*,?
A----------B--------------C-

Part A matches the first element. Part B matches any following elements (notice the star). Part C is the optional comma at the end.

WARNING: Remember to escape backslashes in Java string.

edited Apr 17, 2012 at 7:31

answered Apr 17, 2012 at 7:15

Eser Aygün

8,1041 gold badge22 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Popokoko Over a year ago

Wow, almost perfect. it seems that a string like: "aa|3,aa|4,hi|aa, aa|6" have passed the test :<

Eser Aygün Over a year ago

Oh, I see. Please check the new version. [^,|] matches anything except , and |.

Popokoko Over a year ago

And amazingly, it works! that's quite unbelievable, if ure about to open a regex course, im in! Thanks again!

Popokoko Over a year ago

Im really interested to know if i also understand it: correct me if im wrnog but the first part "[^,|]+\|" says match anything with | at the end (when u excluded ',' and '|' at the beginning) and when using + u expect it to be only this | to end the first part, and the second part "\d+(,[^,|]+\|\d+)*,?" means: "\d" any number + (same sequence from beginning)* when the * notation is the kleene star which lets us define "infinite sets" like u said, and as for the ",?" it means it can end either with or without a ',', have i understand it right?

Eser Aygün Over a year ago

Congrats! You missed only +, or the Kleene plus. A+ means "one or more As". Similarly, [^,|]+ means "one or more non-comma non-pipe characters" and \d+ means "one or more digits". The Kleene star is the "zero or more" version of the same thing.

Mikita Belahlazau · Accepted Answer · 2012-04-17 07:08:08Z

1

I'd suggest splitting your string to array by | delimiter. And validate each part separately. Each part (except first one) should match following pattern \d+(,.*)?

UPDATED

Split by , and validate each part with .*|\d+

edited Apr 17, 2012 at 7:08

answered Apr 17, 2012 at 7:00

Mikita Belahlazau

15.4k2 gold badges41 silver badges44 bronze badges

4 Comments

Marko Topolnik Over a year ago

That doesn't quite make sense given the test input. Comma is the higher-level separator and | is the inner separator.

Mikita Belahlazau Over a year ago

@MarkoTopolnik hm, really. Thanks, I didn't notice it.

Popokoko Over a year ago

Marko is right.. how do u separate between numbers to any other words?

Popokoko Over a year ago

Thank you I am trying at the moment

Collectives™ on Stack Overflow

Java: validating a certain string pattern

2 Answers 2

5 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related