@Override public void schedule(Runnable childStatement){
  Future<Void> submittedStatement=completionService.submit(childStatement,null);
  tasks.add(submittedStatement);
}

@ Override public void schedule ( Runnable childStatement ) { Future < Void > submittedStatement = completionService . submit ( childStatement , null ) ; tasks . add ( submittedStatement ) ; }
schedule a child statement to run
