Question

I want to create a pattern for the following format of string. I have come with the following format but I am stuck as I am not able to scan it properly. Below are the details

Example String: JAS 5F W 123 or BWER34 23 C 23

Above String has the following rules to be followed.

1. The last digits can be 2 or 3 digit numbers only (123 && 023 or
   23)
2. Before that only a single character is allowed case insensitive (W or c)
3. Before that only 2 digits or one digit and a character only “f”or”F” is allowed.

4. Starting of string can be any String alphanumeric string of any length.
   All the parts are separated by space
   I came up with the following String pattern but when i run my java program it gives dangling meta character.

   "*\\s([0-9][fF]|[1-9][0-9])\\s([a-zA-Z])\\s(\\d\\d|\\d\\d\\d)$"
   

Please help me in creating the correct pattern for the above String

Answer 1

First of all you use a quantifier but don’t quantify anything: remove the first * or add something before it. This causes the “dangling metacharacter” message.

Second \\d\\d|\\d\\d\\d could be rewritten to \\d{2,3} (two or three digits).

Finally, you can make the expression case insensitive by adding a (?i) prefix thus allowing you to write it as follows:

"(?i).*\\s(\\df|[1-9]\\d)\\s([a-z])\\s(\\d{2,3})$"

Note that I assume you want to match anything before the query and thus I added a dot before the asterisk: .*. If you use Pattern directly (i.e. not String#matches()) you don’t even need that.

Before that only 2 digits or one digit and a character only “f”or”F” is allowed.

Would that allow 05 as well (those are two digits)? If so, you could rewrite that part as \\df|\\d{2}