code: public static boolean isMixedCase(final CharSequence cs) {
          if (N.isNullOrEmpty(cs) || cs.length() == 1) {
              return false;
          }
  
          boolean containsUppercase = false;
          boolean containsLowercase = false;
          final int len = cs.length();
  
          if (cs.getClass().equals(String.class)) {
              final char[] chars = getCharsForReadOnly((String) cs);
  
              for (int i = 0; i < len; i++) {
                  if (containsUppercase && containsLowercase) {
                      return true;
                  } else if (Character.isUpperCase(chars[i])) {
                      containsUppercase = true;
                  } else if (Character.isLowerCase(chars[i])) {
                      containsLowercase = true;
                  }
              }
          } else {
              for (int i = 0; i < len; i++) {
                  if (containsUppercase && containsLowercase) {
                      return true;
                  } else if (Character.isUpperCase(cs.charAt(i))) {
                      containsUppercase = true;
                  } else if (Character.isLowerCase(cs.charAt(i))) {
                      containsLowercase = true;
                  }
              }
          }
  
          return containsUppercase && containsLowercase;
      }
docs: Copied from Apache Commons Lang: StringUtils#isMixedCase.
  
  @param cs
  @return