I'm trying to create a regular expression in Java to validate a number with the following constraints:
For example: 042004359 is valid, but 0000000000 is not.
\\d+[1-9]\\d* should work, I'd think.
* to a +, and you are home.
* to a +, then this would only accept numbers with at least 2 digits, which I don't think is correct. (As it stands, the [1-9] is mandatory, so that forces at least one digit to be present.)10000 for example. This also implies that the number is at least of length 2.This should do what you need:
/^(?=.*[1-9])([0-9]+)$/
Whilst it matches all of digits [0-9] it contains a lookahead that makes sure there is at least one of [1-9].
I am fairly certain that Java allows can use lookaheads.
EDIT: This regular expression test page seems to imply that it can.
EDIT: If 0 is valid, then you can use this:
^((?=.*[1-9])([0-9]+)|0)$
This will make an exception for 0 on its own (notice the OR operator).
^(\d{1})(\d*?[1-9]{1}\d*)*$
^(\d{1}) - Line must start with 1 digit
(\d*?[1-9]{1}\d*)*$ - Line must end with zero or more 0-9 digits(? for conservative), then 1 1-9 digit, then zero or more digits. This pattern can repeat zero or more times.
Works with:
100000
100100
1010200
1
2
Maybe this is too complicated, lol.
Here's one solution using lookarounds: (?<=\D|^)\d+(?=[1-9])\d*
(?<=\D|^) # lookbehind for non-digit or beginning of line
\d+ # match any number of digits 0-9
(?=[1-9]) # but lookahead to make sure there is 1-9
\d* # then match all subsequent digits, once the lookahead is satisfied
0valid? You say that the number can be any length and the first digit can be 0-9, and apply the restriction that "one of the digits must be non-zero" in the sentence referring to "subsequent digits", but it seems likely you intended that no all-zero number would be valid.