Java ExecutorService: Thread Pools, Callable, Future & Concurrency

Introduced in Java 5 inside java.util.concurrent, the Executor Framework abstracts away the low-level complexities of managing raw thread lifecycles by introducing high-performance Thread Pools.

Using ExecutorService & Callable<V>

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.Callable;

public class ExecutorServiceDemo {
    public static void main(String[] args) throws Exception {
        // Create a fixed thread pool with 3 worker threads
        ExecutorService executor = Executors.newFixedThreadPool(3);

        // Submit a Callable task that returns a computed result
        Callable<Integer> calculation = () -> {
            System.out.println("Processing complex calculation on " + Thread.currentThread().getName());
            Thread.sleep(1000);
            return 42 * 10;
        };

        // Submit returns a Future holding the asynchronous result
        Future<Integer> futureResult = executor.submit(calculation);

        System.out.println("Main thread continues doing other work...");
        
        // .get() blocks until the worker thread produces the result:
        Integer result = futureResult.get();
        System.out.println("Calculation Result: " + result); // 420

        // Always shutdown executors cleanly!
        executor.shutdown();
    }
}