Check non-numeric characters in string

Question

I want to check whether the String contains only numeric characters or it contains alpha-numeric characters too.

I have to implement this check in database transaction where about a hundred-thousand records are going to be fetched and passed through this check, so I need optimized performance answer.

Currently, I have implemented this through a try-catch block: I parsed the string in Integer in try block and checked for the NumberFormatException in the catch block. Please suggest if I'm wrong.

Answer 1

You can check this with a regex.

Suppose that (numeric values only):

String a = "493284835";
a.matches("^[0-9]+$"); // returns true

Suppose that (alphanumeric values only):

String a = "dfdf4932fef84835fea";
a.matches("^([A-Za-z]|[0-9])+$"); // returns true

As Pangea said in the comments area :

If the performance are critical, it's preferrable to compile the regex. See below for an example :

String a = "dfdf4932fef84835fea";
Pattern pattern = Pattern.compile("^([A-Za-z]|[0-9])+$");
Matcher matcher = pattern.matcher(a);

if (matcher.find()) {
    // it's ok
}

Answer 2

Just Googling, I found out this link

 public boolean containsOnlyNumbers(String str) {        
        //It can't contain only numbers if it's null or empty...
        if (str == null || str.length() == 0)
            return false;

        for (int i = 0; i < str.length(); i++) {

            //If we find a non-digit character we return false.
            if (!Character.isDigit(str.charAt(i)))
                return false;
        }

        return true;
    }

Edit: A RegExp to check numeric should be :

return yourNumber.matches("-?\\d+(.\\d+)?");