Java: What is the difference between ExecutorService and ForkJoinPool?

1// ExecutorService
2ExecutorService executor = Executors.newFixedThreadPool(4);
3executor.submit(() -> doWork());
4executor.shutdown();
5
6// ForkJoinPool
7ForkJoinPool pool = new ForkJoinPool(4);
8ForkJoinTask<Long> task = new RecursiveTask<Long>() {
9    protected Long compute() {
10        if (size <= THRESHOLD) {
11            return sequentialCompute();
12        }
13        ForkJoinTask<Long> left = subtask(leftHalf).fork();
14        Long right = subtask(rightHalf).compute();
15        Long leftResult = left.join();
16        return combine(leftResult, right);
17    }
18};