public synchronized Invoker<V> invoke() throws UncompletedInvokeException {
  if (future != null && !future.isDone()) {
    throw new UncompletedInvokeException(this);
  }
  future=executor.submit(this);
  return this;
}

public synchronized Invoker < V > invoke ( ) throws UncompletedInvokeException { if ( future != null && ! future . isDone ( ) ) { throw new UncompletedInvokeException ( this ) ; } future = executor . submit ( this ) ; return this ; }
invoke the server remote method and just simply return this
