/**
   * Returns a copy of the input string in which all {@linkplain #isLowerCase(char) lowercase ASCII
   * characters} have been converted to uppercase. All other characters are copied without
   * modification.
   */
  public static String toUpperCase(String string) {
    int length = string.length();
    for (int i = 0; i < length; i++) {
      if (isLowerCase(string.charAt(i))) {
        char[] chars = string.toCharArray();