Explain Difference between Future and CompletableFuture classes in Java

The Future and CompletableFuture classes in Java both represent asynchronous computations, but they have some differences in terms of functionality and usage.

Future:

• Syntax:

  Future<ResultType> future = executorService.submit(Callable<ResultType> task);

• Example:

ExecutorService executor = Executors.newFixedThreadPool(1);
Future<String> future = executor.submit(() -> {
    Thread.sleep(2000); // Simulate a time-consuming task
    return "Hello, from Future!";
});
String result = future.get(); // Blocking call to get the result
System.out.println(result);
executor.shutdown();

CompletableFuture:

• Syntax:

  CompletableFuture<ResultType> future = CompletableFuture.supplyAsync(Supplier<ResultType> supplier);

• Example:

CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    try {
        Thread.sleep(2000); // Simulate a time-consuming task
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return "Hello, from CompletableFuture!";
});
future.thenAccept(result -> System.out.println(result)); // Non-blocking callback

• Differences:

1. Completion Handling: Future relies on blocking methods like get() for result retrieval, while CompletableFuture provides non-blocking methods like thenAccept() for completion handling.
2. Composition: CompletableFuture supports fluent API and allows chaining of multiple asynchronous operations, whereas Future does not.
3. Explicit Completion: CompletableFuture allows explicit completion via methods like complete() or completeExceptionally(), which can be useful in certain scenarios.

Poll:

Which Java related Questions would you like to read more about?

• Java 8, 11, 17 feature
• Streams
• Spring, Spring Boot
• Multi Threading
• Design Patterns

Leave a comment below!

---

Discover the more Java interview question for experienced developers! YouTube Channel Link