Java Data Type - 如何get string length不使用length()方法

public class Main {
  public static void main(String... args) {
    System.out.println("\nName Length is:" + len("w3cschool.cn"));
  }

  public static int len(String ab) {
    char[] ac = ab.toCharArray();
    int i = 0, k = 0;

    for (i = 0, k = 0; ac[i] != '\0'; i++){
      k++;
    }
    return k;
  }
}