检查字符串是否没有任何字母而只有数字

Question

How can I check if a String in java has no letters, only numbers? Thank you for the answer

Answer 1

You can use regex: yourString.matches("\\\\d+")

\\\\d means one digit 0-9, + means one or more, combined \\\\d+ is equal to one or more digit :)

Answer 2

Use a regular expression:

string.matches("\\d*");

"\\d*" means "A digit (0-9) zero or more times." Alternatively, you can replace "*" with "+" to mean "one or more times".

Answer 3

org.apache.commons.lang.StringUtils.isNumeric(String) verifies that all characters in the input string are digits.

It's implemented as (if you don't want the 3rd-party dependency):

    int sz = str.length();
    for (int i = 0; i < sz; i++) {
        if (Character.isDigit(str.charAt(i)) == false) {
            return false;
        }
    }
    return true;

Answer 4

You can just iterate over the string and check each character (possibly more efficient than doing it with a regex, if performance is a consideration).

boolean isAllDigit(String s) {
    for (int i = 0; i < s.length(); i++) {
      if (s.charAt(i) < '0' || s.charAt(i) > '9') {
        return false;
      }
    }

   return true;
}

Answer 5

Why don't you just put it in a try/catch?

    String number="a123.2";
    try {
        Double.parseDouble(number);
        System.out.println("It's a number");
    } catch (Exception e) {
        System.out.println("This is not a number!");
    }