code: private void writeObject(ObjectOutputStream stream) throws IOException {
      stream.defaultWriteObject();
      stream.writeInt(size);
      for (int i = firstEntryIndex(); i >= 0; i = getSuccessor(i)) {
        stream.writeObject(keys[i]);
        stream.writeObject(values[i]);
      }
    }
docs: The serial form currently mimics Android's java.util.HashMap version, e.g. see
  http://omapzoom.org/?p=platform/libcore.git;a=blob;f=luni/src/main/java/java/util/HashMap.java