Regular expression to check allowed characters not working in Java

Question

I have the following method to check allowed characters:

private boolean checkIfAllCharsAreValid(String test) {
    boolean valid = false;
    if (test.matches("^[a-zA-Z0-9,.;:-_'\\s]+$")) {
        valid = true;
    }
    return valid;
}

but if test has the character - in it the match return false. Do i have to escape the - ?

Answer 1

Inside [ ... ] the - symbol is treated specially. (You use it yourself in this special purpose in the beginning of your expression where you have az .)

You need to escape the - character

[a-zA-Z0-9,.;:\-_'\s]
              ^

or put it last (or first) in the [...] expression like

[a-zA-Z0-9,.;:_'\s-]
                   ^

---

Some further notes:

• Technically speaking all characters are valid in the empty string, so I would change from + to * in your expression.

• String.matches checks the full string, so the ^ and $ are redundant.

• Your entire method could be wirtten as

   return test.matches("[a-zA-Z0-9,.;:_'\\\\s-]*"); 

Answer 2

A - in a character class surrounded on both sides is a regex meta character to denote range.

To list a literal - in a char class you escape the - in the char class:

if (test.matches("^[a-zA-Z0-9,.;:\\-_'\\s]+$")) 
                                 ^^^ 

or place the - at the end of char class:

if (test.matches("^[a-zA-Z0-9,.;:_'\\s-]+$")) 
                                      ^

or place the - at the beginning of char class:

if (test.matches("^[-a-zA-Z0-9,.;:_'\\s]+$")) 
                    ^

Answer 3

您可以将-放在字符组的开头，以便它不会被解释为字符范围。