Given the code fragment: var pool = Executors.newFixedThreadPool(5); Future<Integer> result = pool.submit(() -> 1); Which type of lambda expression is passed into submit()?

Question

Options

• Ajava.lang.Runnable
• Bjava.util.function.Predicate
• Cjava.util.function.Function
• Djava.util.concurrent.Callable

• A
  6% (3)
• B
  12% (6)
• C
  2% (1)
• D
  80% (41)

Explanation

Callable<Integer> is correct because the lambda () -> 1 takes no arguments and returns an Integer - which matches Callable's single abstract method V call() throws Exception. The compiler resolves the submit() overload to submit(Callable<T>) (not submit(Runnable)) precisely because a return type is present, yielding a Future<Integer>.

Why the distractors fail:

• A (Runnable): Runnable.run() is void - it cannot return a value, so () -> 1 would not compile as a Runnable, and submit(Runnable) returns Future<?>, not Future<Integer>.
• B (Predicate): Predicate<T>.test(T t) requires one argument and returns boolean - the lambda has no parameters, so it can't match.
• C (Function): Function<T,R>.apply(T t) also requires one argument - again, the zero-argument lambda is incompatible.

Memory tip: Think "Callable = Capable of returning a value." If your lambda returns something meaningful and you want a typed Future<T> back from submit(), it's always Callable. Runnable is the fire-and-forget sibling that returns nothing.

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