What is the difference between ExecutorService and CompletionService?

Can you explain the difference between ExecutorService and CompletionService in Java?

Sure! ExecutorService is an interface that provides a higher-level replacement for managing threads, while CompletionService is used to facilitate the completion of asynchronous tasks.

How do I use CompletionService with ExecutorService?

You can use CompletionService by wrapping an ExecutorService instance. It allows you to submit tasks and retrieve their results as they complete.

Can you give me a code example of using both?

Absolutely! Here's a simple example:

ExecutorService executor = Executors.newFixedThreadPool(2);
CompletionService<String> completionService = new ExecutorCompletionService<>(executor);

for (int i = 0; i < 5; i++) {
    final int taskId = i;
    completionService.submit(() -> {
        Thread.sleep(1000);
        return "Task " + taskId + " completed";
    });
}

for (int i = 0; i < 5; i++) {
    Future<String> future = completionService.take();
    System.out.println(future.get());
}
executor.shutdown();

What are the advantages of using CompletionService?

CompletionService simplifies handling the results of asynchronous tasks, allowing you to process them as they complete, which can improve efficiency.