Kodejava

How do I check if a character representing a number?

Category: java.lang, viewed: 21K time(s).

For validation purposes we might need to check if data entered by our users is a valid data for our application to process. A simple mechanism for checking if a character inputted is a digit or not can be done by using the java.lang.Character class isDigit(char c) method. An example is shown below:

package org.kodejava.example.lang;

public class CharacterIsDigit {
    public static void main(String[] args) {
        String str = "123ABC456def789HIJ0";

        for (int i = 0; i < str.length(); i++) {
            //
            // Determines if the specified character is a digit
            //
            if (Character.isDigit(str.charAt(i))) {
                System.out.println(str.charAt(i)
                        + " is a digit.");
            } else {
                System.out.println(str.charAt(i)
                        + " not a digit.");
            }
        }
    }
}

These are the outputs of our program:

1 is a digit.
2 is a digit.
3 is a digit.
A not a digit.
B not a digit.
C not a digit.
4 is a digit.
5 is a digit.
6 is a digit.
d not a digit.
e not a digit.
f not a digit.
7 is a digit.
8 is a digit.
9 is a digit.
H not a digit.
I not a digit.
J not a digit.
0 is a digit.