How to Check If the String Contains Only Letters or Digits

In this post, we will write a Java program to check if the String contains only Unicode letters or digits.
Program explanation:
  • This program uses Character.isLetterOrDigit(cs.charAt(i) method to check if the character is letter or digit.
  • testIsAlphanumeric() - JUnit test case for testing this program.

Java program to checks If the String Contains Only Letters or Digits

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

 * Program to Checks if the CharSequence contains only Unicode letters or digits
 * @author
public class IsAlphanumericExample {

    public static boolean isEmpty(final CharSequence cs) {
        return cs == null || cs.length() == 0;

    public static boolean isAlphanumeric(final CharSequence cs) {
        if (isEmpty(cs)) {
            return false;
        final int sz = cs.length();
        for (int i = 0; i < sz; i++) {
            if (!Character.isLetterOrDigit(cs.charAt(i))) {
                return false;
        return true;

    public void testIsAlphanumeric() {
        assertFalse(isAlphanumeric(" "));
        assertFalse(isAlphanumeric("ham kso"));

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