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copied!<p>Define a callback interface to receive whatever parameters you want to pass along in the completion notification. Then invoke it at the end of the task. </p> <p>You could even write a general wrapper for Runnable tasks, and submit these to <code>ExecutorService</code>. Or, see below for a mechanism built into Java 8.</p> <pre><code>class CallbackTask implements Runnable { private final Runnable task; private final Callback callback; CallbackTask(Runnable task, Callback callback) { this.task = task; this.callback = callback; } public void run() { task.run(); callback.complete(); } } </code></pre> <hr> <p>With <a href="http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html" rel="noreferrer"><code>CompletableFuture</code></a>, Java 8 included a more elaborate means to compose pipelines where processes can be completed asynchronously and conditionally. Here's a contrived but complete example of notification.</p> <pre><code>import java.util.concurrent.CompletableFuture; import java.util.concurrent.ThreadLocalRandom; import java.util.concurrent.TimeUnit; public class GetTaskNotificationWithoutBlocking { public static void main(String... argv) throws Exception { ExampleService svc = new ExampleService(); GetTaskNotificationWithoutBlocking listener = new GetTaskNotificationWithoutBlocking(); CompletableFuture<String> f = CompletableFuture.supplyAsync(svc::work); f.thenAccept(listener::notify); System.out.println("Exiting main()"); } void notify(String msg) { System.out.println("Received message: " + msg); } } class ExampleService { String work() { sleep(7000, TimeUnit.MILLISECONDS); /* Pretend to be busy... */ char[] str = new char[5]; ThreadLocalRandom current = ThreadLocalRandom.current(); for (int idx = 0; idx < str.length; ++idx) str[idx] = (char) ('A' + current.nextInt(26)); String msg = new String(str); System.out.println("Generated message: " + msg); return msg; } public static void sleep(long average, TimeUnit unit) { String name = Thread.currentThread().getName(); long timeout = Math.min(exponential(average), Math.multiplyExact(10, average)); System.out.printf("%s sleeping %d %s...%n", name, timeout, unit); try { unit.sleep(timeout); System.out.println(name + " awoke."); } catch (InterruptedException abort) { Thread.currentThread().interrupt(); System.out.println(name + " interrupted."); } } public static long exponential(long avg) { return (long) (avg * -Math.log(1 - ThreadLocalRandom.current().nextDouble())); } } </code></pre>

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