Given the code fragment:

class CallerThread implements Callable {

String str;

public CallerThread(String s) {this.str=s;}

public String call() throws Exception {

return str.concat("Call");

}

}

and

public static void main (String[] args) throws InterruptedException, ExecutionException

{

ExecutorService es = Executors.newFixedThreadPool(4); //line n1

Future f1 = es.submit (newCallerThread("Call"));

String str = f1.get().toString();

System.out.println(str);

}

Which statement is true?