I am using a regex to program an input validator for a text box where I only want alphabetical characters. I was wondering if [A-z] and [a-zA-Z] were equivalent or if there were differences performance wise.
I keep reading [a-zA-Z] on my searches and no mention of [A-z].
I am using java's String.matches(regex).
[A-z] will match ASCII characters in the range from A to z, while [a-zA-Z] will match ASCII characters in the range from A to Z and in the range from a to z. At first glance, this might seem equivalent -- however, if you look at this table of ASCII characters, you'll see that A-z includes several other characters. Specifically, they are [, \, ], ^, _, and ` (which you clearly don't want).
When you take a look at the ASCII table, you will see following:
A = 65
Z = 90
a = 97
z = 122
So, [A-z] will match every char from 65 to 122. This includes these characters (91 -> 96) as well:
[\]^_`
This means [A-Za-z] will match only the alphabet, without the extra characters above.
The a-z matchs 'a' to 'z' A-Z matchs 'A' to 'Z' A-z matches all these as well as the characters between the 'Z' and 'a' which are [ ] ^ / _ `
Refer to http://www.asciitable.com/
Take a look at ASCII table. You'll see that there are some characters between Z and a, so you will match more than you intented to.
The square brackets create a character class and the hyphen is a shorthand for adding every character between the two provided characters. i.e. [A-F] can be written [ABCDEF].
The character class [A-z] will match every character between those characters, which in ASCII includes some other characters such as '[', '\' and ']'.
An alternative to specifying both cases would be to set the regular expression to be case-insensitive, by using the /i modifier.
Take a look at the ASCII chart (which Java characters are based on): there are quite a few punctuation characters situated between Z and a, namely these:
[\]^ _`
