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import java.util.*;
import java.util.concurrent.*;

public class ExecutorServiceDemo {

static int fibonacci(int n) {
        if (n <= 1) return n;
        return fibonacci(n - 1) + fibonacci(n - 2);
    }

public static void main(String[] args) throws InterruptedException, ExecutionException {
        // Fixed thread pool with 3 workers
        ExecutorService executor = Executors.newFixedThreadPool(3);

// Submit Callable tasks that return results
        List<Future<Integer>> futures = new ArrayList<>();
        int[] inputs = {10, 15, 20, 25, 30};

for (int n : inputs) {
            Future<Integer> future = executor.submit(() -> fibonacci(n));
            futures.add(future);
        }

// Collect results
        for (int i = 0; i < inputs.length; i++) {
            try {
                int result = futures.get(i).get(5, TimeUnit.SECONDS);
                System.out.printf("fibonacci(%d) = %d%n", inputs[i], result);
            } catch (TimeoutException e) {
                System.out.println("Task " + i + " timed out");
                futures.get(i).cancel(true);
            }
        }

// Proper shutdown
        executor.shutdown();
        boolean done = executor.awaitTermination(10, TimeUnit.SECONDS);
        System.out.println("Executor terminated cleanly: " + done);

// ScheduledExecutorService example
        ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
        scheduler.scheduleAtFixedRate(
            () -> System.out.println("Tick at " + System.currentTimeMillis()),
            0, 200, TimeUnit.MILLISECONDS);
        Thread.sleep(700);
        scheduler.shutdownNow();
    }
}