What are some examples of using Future and Callable in Java?

What are some examples of using Future and Callable in Java?

In Java, the Future and Callable interfaces are used for asynchronous programming. A Callable can return a result and can throw a checked exception, while Future represents the result of an asynchronous computation. Here's a simple example:

import java.util.concurrent.*;

public class CallableExample {
    public static void main(String[] args) throws Exception {
        ExecutorService executor = Executors.newFixedThreadPool(2);
        Callable<Integer> task = () -> {
            Thread.sleep(2000);
            return 123;
        };
        Future<Integer> future = executor.submit(task);
        System.out.println("Task submitted.");
        Integer result = future.get(); // This will block until the result is available
        System.out.println("Result: " + result);
        executor.shutdown();
    }
}

Can you explain how to handle exceptions with Callable?

Certainly! When using Callable, you can throw checked exceptions. To handle exceptions, you can catch them when calling future.get(). Here's an example:

try {
    Integer result = future.get();
} catch (ExecutionException e) {
    System.out.println("Exception occurred: " + e.getCause());
} catch (InterruptedException e) {
    Thread.currentThread().interrupt();
}

What is the difference between Runnable and Callable?

The main difference is that Runnable cannot return a result or throw checked exceptions, while Callable can return a result and throw exceptions. Callable is more flexible for tasks that require a return value.

Can you give me a real-world scenario where Callable is useful?

Sure! A real-world scenario could be a web server handling multiple requests. Each request can be processed in a separate thread using Callable, allowing the server to return results asynchronously, improving performance and responsiveness.