@Override public void writeExternal(ObjectOutput out) throws IOException {
  out.writeInt(this.parent);
  out.writeUTF(this.componentType);
  if (this.id != null) {
    out.writeUTF(this.id);
  }
 else {
    out.writeUTF(NULL_ID);
  }
}

@ Override public void writeExternal ( ObjectOutput out ) throws IOException { out . writeInt ( this . parent ) ; out . writeUTF ( this . componentType ) ; if ( this . id != null ) { out . writeUTF ( this . id ) ; } else { out . writeUTF ( NULL_ID ) ; } }
write the tree node out .
