code: public static AsciiString cached(String string) {
          AsciiString asciiString = new AsciiString(string);
          asciiString.string = string;
          return asciiString;
      }
docs: Returns an {@link AsciiString} containing the given string and retains/caches the input
  string for later use in {@link #toString()}.
  Used for the constants (which already stored in the JVM's string table) and in cases
  where the guaranteed use of the {@link #toString()} method.