在Java中，如何检查字符串是否同时包含字母和数字，但仅包含字母和数字？

Question

I tried this:

private static void isLetterandNumberCombo(Tokens token) {
    if (token.getContents().matches("^(?=.*[A-Z])(?=.*[0-9])[A-Z0-9]+$")){
        token.setValid(false);
    }
} 

but the input 123f45 still does not set the token to valid as I thought it would

Answer 1

Your solution is fine. You just need to add the case-insensitive flag ( (?i) ) to match lowercase letters. And matches() looks for a full match, so you don't need the anchors at the beginning and end:

(?i)(?=.*[A-Z])(?=.*[0-9])[A-Z0-9]+

Answer 2

Give this a whirl

private static boolean isLetterandNumberCombo(Tokens token) {
    String regex = "^[a-zA-Z0-9]+$";
    Pattern pattern = Pattern.compile(regex);

    return pattern.matcher(token.getContents()).matches();
}

You'll get back true or false if the token is valid.

Answer 3

I would go with:

^[A-Za-z\d]*(([A-Za-z]\d)|(\d[A-Za-z]))[A-Za-z\d]*$

The idea is that a valid string will have either a letter followed by a number or the opposite somewhere, and other optional letters or numbers before or after.

Answer 4

A simple regex would do the job:

Change your function to:

private static void isLetterandNumberCombo(Tokens token) {
  token.setValid(token.getContents() != null && token.getContents().matches("[a-zA-Z0-9]+"));
}