Regex expression: [A-Z]([^0-9]|[^A-Z]) [A-Z]
The requirements are that the string should start and end with a capital letter A-Z, and contain at least one number in between. It should not have anything else besides capital letters on the inside. However, it's accepting spaces and punctuation too.
My expression fails the following test case A65AJ3L 3F,D due to the comma and whitespace.
Why does this happen when I explicitly said only numbers and uppercase letters can be in the string?
CodePudding user response：
^[A-Z0-9\s,] $
For Test Regex
String regex = "^[A-Z0-9\\s,] $";
Pattern p = Pattern.compile(regex);
CodePudding user response：
Starting the character class with [^ makes is a negated character class.
Using ([^0-9]|[^A-Z]) matches any char except a digit (but does match A-Z), or any char except A-Z (but does match a digit).
This way it can match any character.
If you would turn it into [A-Z]([0-9]|[A-Z]) [A-Z] it still does not make it mandatory to match at least a single digit on the inside due to the alternation | and it can still match AAA for example.
You might use:
^[A-Z] [0-9][A-Z0-9]*[A-Z]$
The pattern matches:
^Start of string[A-Z]Match 1 times A-Z[0-9]Match a single digit[A-Z0-9]*Optionally match either A-Z or 0-9[A-Z]Match a single char A-Z$End of string