Hi there

I am very new to regex expressions in JAVA. I have the following requirements to validate a password:

1) password length of minumum 10 characters

2) at least 4 letters, anywhere in the password

3) at least 4 numbers, anywhere in the password

4) No special characters
 

Any help would greatly be appreciated.

 

Have a look at this thread:

http://regexadvice.com/forums/thread/45852.aspx

Thank you for your response. 

I tried the regex expression in that thread, but I am still not getting it right.

I am validating this string: GH43S3UU74

with this regex: ^(?=.{8,})(?=.*?\d)(?=.*?[a-z])(?=.*?[A-Z])(?=.*?[-#!$%_=+<>]).*$

 

and it still fails. Also, where do I specify the minimum number of characters for the letters and the numbers?

Well, that's not surprising: I see you just copied and pasted the regex from that other thread. Are your requirements and the requirements in that other thread the same?

Yes I did copy and paste it, but the string that I am trying to validate should pass right?

Here's an explanation of that regex:

^                     the start of the string
(?=.{8,})             when looking ahead, there must be at least 8 characters of any type
(?=.*?\d)             when looking ahead, there must be at least 1 digit
(?=.*?[a-z])          when looking ahead, there must be at least 1 lower case letter
(?=.*?[A-Z])          when looking ahead, there must be at least 1 upper case letter
(?=.*?[-#!$%_=+<>])   when looking ahead, there must be at least 1 of the following characters: -, #, !, $, %, _, =, +, < or >
.*                    zero or more characters
$                     the end of the string

Thanks for that explanation, it makes more sense now.

So I changed my expression to look like this: ^(?=.{10,})(?=.{4,}?\\d)(?=.*{4,}[a-zA-Z]).*$

But when I validate this string "GJK2VNDHS1", it passes when it should fail because there are only 2 numbers when 4 are required. Have I set up the occurrences in the pattern incorrectly?

The same for this string "9692D63C49", it passes when it should fail because there are only 2 letters when 4 are required.

 

 

Another explanation (I left out one of the ? mark, since it's not really needed in this case):

(?=A)          when looking ahead, there must be an 'A' straight away
(?=.A)         when looking ahead, there can be any (single) character, followed by an 'A'
(?=.*A)        when looking ahead, there can be any number of characters, followed by an 'A' (this is
               the same as when saying: "when looking ahead, there must be at least one 'A'")
(?=.*A.*A)     when looking ahead, there must be at least two 'A'
(?=(.*A){2})   exactly the same as the previous

Thanks, it works perfectly now.

seedollar:

Thanks, it works perfectly now.

Good to hear it, you're welcome of course!