Question

I am trying to create a string of six alphanumeric characters. The code below works fine most of the time but on the rare occasion a string of six alpha characters gets through, how can I ensure that the returned string is always alphanumeric?

String code = "";

while(!code.matches("[a-zA-Z0-9]+$"))
{
    code = Integer.toString((int) (Math.random() * Integer.MAX_VALUE), 36);
}

return code;

Answer 1

Repeated attempts is possibly the simplest, but you have to check it contains a letter and a digit.

String code;
do {
    code = Integer.toString((int) (Math.random() * Integer.MAX_VALUE), 36);
    if (code.length() > 6)
       code = code.substring(0, 6);
} while(!code.matches(".*\\w.*") || !code.matches(".*\\d.*") || code.length() < 6);