Regular expression in Java for positive integers (excluding those starting with zero)

Question

I currently use "(\d){1,9}", but it fails to invalidate numbers such as "0134". The expression must only validate numbers that are positive INTEGERS. Thanks.

Answer 1

Right now you use the expression [0-9]{1,9}, so this clearly allows the number 0134. When you want to require that the first character is not a zero, you have to use [1-9][0-9]{0,8}.

By the way: 0134 is a positive integer. It is an integer number, and it is positive. ;)

edit:

To prevent integer overflow you can use this pattern:

• [1-9][0-9]{0,8}
• [1-1][0-9]{9}
• [2-2][0-1][0-9]{8}
• [2-2][1-1][0-3][0-9]{7}
• [2-2][1-1][4-4][0-6][0-9]{6}
• …

I think you get the idea. Then you combine these expressions with |, and you are done.

Alternatively, have a look at the Integer.valueOf(String) method, how it parses numbers and checks for overflow. Copy that code and change the part with the NumberFormatException.