code: public static boolean isAllLowerCase(final String cs) {
          if (Strings.isNullOrEmpty(cs)) {
              return false;
          }
          final int sz = cs.length();
          for (int i = 0; i < sz; i++) {
              if (!Character.isLowerCase(cs.charAt(i))) {
                  return false;
              }
          }
          return true;
      }
docs: <p>Checks if the CharSequence contains only lowercase characters.
  
  <p>{@code null} will return {@code false}.
  An empty CharSequence (length()=0) will return {@code false}.
  
  <pre>
  StringUtils.isAllLowerCase(null)   = false
  StringUtils.isAllLowerCase("")     = false
  StringUtils.isAllLowerCase("  ")   = false
  StringUtils.isAllLowerCase("abc")  = true
  StringUtils.isAllLowerCase("abC")  = false
  StringUtils.isAllLowerCase("ab c") = false
  StringUtils.isAllLowerCase("ab1c") = false
  StringUtils.isAllLowerCase("ab/c") = false
  </pre>
  
  @param cs  the CharSequence to check, may be null
  @return {@code true} if only contains lowercase characters, and is non-null
  @since 2.5
  @since 3.0 Changed signature from isAllLowerCase(String) to isAllLowerCase(CharSequence)