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More on character classes
We looked at some basic regular expressions that included character classes: a "choice" of character to match placed inside square brackets. For example, [Tt] will match against either T or t. On this page we'll look at some more possibilities with character classes.
A useful feature is that we can put a range of characters by placing a hyphen between start and end character. For example, to match any lower case letter, we can write:
Similarly, to match a digit, we can write:
We can combine single characters and ranges, and/or combine multiple ranges:
To say "not in the range...", we put a hat symbol ^ at the beginning of the character class expression. So for example, to say "not a digit", we would write the following:
An operation called intersection essentially means "in this class AND in this one". It is really useful when we combine an intersection with a negation to say "in this class BUT NOT in this one". The intersection uses two ampersands. Here is the syntax:
The first of these says a digit except 5; the second says any lower case letter except those representing vowels.
Note that one ampersand on its own– &– simply represents that character.
Named character classes
Some 'shortcuts' exist for common character classes (such as [0-9]) in the form of named character classes.
On the next page, we'll look at a special character class: the dot.
Written by Neil Coffey. Copyright © Javamex UK 2012. All rights reserved.