Java determine if a string has alphanumeric characters or not

/**
 * @author lautturi.com
 * Java example: Java determine whether a string contains alphanumeric characters
 */

import java.util.*;

public class Lautturi {

	public static void main(String[] args) {

		String str = "hello lautturi!";
		for(int i=0;i<str.length();i++) {
			
			char ch = str.charAt(i);
			if(!Character.isLetterOrDigit(ch)) {
				System.out.println(ch + " is not a alphanumeric char");
			}
		}
	}

}

output:

is not a alphanumeric char
! is not a alphanumeric char