Check if a string contains only digits.

public class Test {

    public static void main(String[] args) {
        String string = "3487374 abc";
        boolean ans = checkDigit(string);
        if (ans) {
            System.out.println("String contains only digits");
        } else {
            System.out.println("String contains both digits and alphabates");
        }
    }

    private static boolean checkDigit(String string) {
        string = string.replaceAll(" ", "");
        boolean ans = false;
        for (int i = 0; i < string.length() - 1; i++) {
            if (string.charAt(i) >= 48 && string.charAt(i) <= 57) {
                ans = true;
            } else {
                return false;
            }
        }
        return ans;
    }
}