Java 9 introduces a couple of improvements in CompletableFuture API. Today let’s take a look at new delayedExecutor static method.

static Executor delayedExecutor(long delay, TimeUnit unit);

//Returns a new Executor that submits a task to the default executor after the given delay.

static Executor delayedExecutor(long delay, TimeUnit unit, Executor executor); 

//Returns a new Executor that submits a task to the given base executor after the given delay.

Let’s say we want to delay the execution for 5 seconds:

long start = System.currentTimeMillis();

CompletableFuture future = new CompletableFuture<>();
future.completeAsync(() -> "Inside task", CompletableFuture.delayedExecutor(5, SECONDS))
    .thenAccept(result -> System.out.println("accept: " + result))
    .get();

long end = System.currentTimeMillis();

//output

accept: Inside future task
task starts after 5 seconds