I Like this one.

private static final int NUMBER_MAX_LENGTH = String.valueOf(Long.MAX_VALUE).length();

public static boolean isNumber(String string) {
    if (string == null || string.isEmpty()) {
        return false;
    }
    if (string.length() >= NUMBER_MAX_LENGTH) {
        try {
            Long.parseLong(string);
        } catch (Exception e) {
            return false;
        }
    } else {
        int i = 0;
        if (string.charAt(0) == '-') {
            if (string.length() > 1) {
                i++;
            } else {
                return false;
            }
        }
        for (; i < string.length(); i++) {
            if (!Character.isDigit(string.charAt(i))) {
                return false;
            }
        }
    }
    return true;
}

http://stackoverflow.com/questions/15111420/how-to-check-if-a-string-contains-only-digits-in-java

Q:

In Java for String class there is a method called matches, how to use this method to check if my string is having only digits using regular expression. I tried with below examples, but both of them returned me false as result.

String regex = "[0-9]"; String data = "23343453"; System.out.println(data.matches(regex));

String regex = "^[0-9]"; String data = "23343453";System.out.println(data.matches(regex));

Answer:

Try

String regex = "[0-9]+";

or

String regex = "\\d+";

Where the + means "one or more" and \d means "digit".

Note: the "double slash" gives you one slash. "\\d" gives you: \d

You must allow for more than a digit (the + sign) as in:

String regex = "[0-9]+"; 
String data = "23343453"; 
System.out.println(data.matches(regex));

Answer:
http://www.pretechsol.com/2013/10/how-to-check-if-string-contains-only.html#.UmgRIxAVuPA
private static boolean isNumber(final String number) {
        boolean bisNumber = false;

        if (number == null) {

            bisNumber = false;

        }

        try {

            Integer.parseInt(number);

            bisNumber = true;

        } catch (NumberFormatException ne) {

            bisNumber = false;

        }

        return bisNumber;

    }