👀 Views: 88 💬 Answers: 1 📅 Created: 2025-06-09

java completablefuture asynchronous javase11 Java

I'm working through a tutorial and I'm getting frustrated with I'm having trouble with I'm working with an scenario where I have multiple dependent tasks using `CompletableFuture` in Java 11, and they're not executing in the order I expect. I created a pipeline of asynchronous tasks, but sometimes the second task seems to start before the first one completes, leading to inconsistent results. Here's the code I'm using: ```java CompletableFuture<String> task1 = CompletableFuture.supplyAsync(() -> { // Simulating a long-running task try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } return "Result from Task 1"; }); CompletableFuture<String> task2 = task1.thenApply(result -> { // This task depends on the result of task1 System.out.println(result); return "Result from Task 2"; }); CompletableFuture<String> task3 = task2.thenApply(result -> { // This task also depends on task2 System.out.println(result); return "Result from Task 3"; }); task3.thenAccept(finalResult -> System.out.println(finalResult)); ``` When I run this, I sometimes get output that indicates `Task 2` is executing before `Task 1` has finished, which leads to `null` being printed instead of the expected result from `Task 1`. I've ensured that the tasks are set up to depend on each other properly by chaining them. I also checked whether there are multiple `ExecutorService` instances running concurrently, but it seems I should be okay since I'm using the default ForkJoinPool. I'm not explicitly configuring any thread pool or executor, so I'm unsure why this is happening. Are there any best practices I might have overlooked while using `CompletableFuture`, or is there something specific about asynchronous execution in Java 11 that could lead to this behavior? What's the best practice here? This is part of a larger desktop app I'm building. Any pointers in the right direction? I'm coming from a different tech stack and learning Java. I'd love to hear your thoughts on this.