Given the code fragments: `` class R implements Runnable { public void run() { System.out.println("Run..."); } } class C implements Callable<String> { public String call() throws Exception { return…

Question

class R implements Runnable {
 public void run() { System.out.println("Run..."); }
}

class C implements Callable<String> {
 public String call() throws Exception { return "Call..."; }
}

ExecutorService es = Executors.newSingleThreadExecutor();
es.execute(new R()); // line n1
Future<String> f1 = es.submit(new C()); // line n2
System.out.println(f1.get());
es.shutdown();

Options

• AThe program prints Run... and throws an exception.
• BA compilation error occurs at line n1.
• CRun...
• DA compilation error occurs at line n2.

• A
  12% (5)
• B
  7% (3)
• C
  79% (33)
• D
  2% (1)

Explanation

Option C is correct because both lines compile and run without error: ExecutorService.execute() accepts a Runnable, and ExecutorService.submit() accepts a Callable<T>, so both n1 and n2 are valid API calls. The executor runs R.run(), printing Run..., then C.call() returns "Call...", which f1.get() retrieves and println prints - giving the full output Run... followed by Call....

Why the distractors are wrong:

• B is wrong because execute(Runnable) is a perfectly valid method on ExecutorService - no compilation error.
• D is wrong because submit(Callable<V>) is also a valid overload - ExecutorService has separate overloads for Runnable and Callable.
• A is wrong because C.call() returns normally (no exception is thrown), so f1.get() completes without an ExecutionException.

Memory tip: Think of the two methods by what they give back - execute is fire-and-forget (returns void), while submit gives you a Future to retrieve a result later. If a question asks about execute with a Callable or submit with a Runnable returning a Future<?>, those compile too - just remember execute never returns a result regardless.

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