What is FutureTask in Java?

FutureTask is a class that implements the Runnable and Future interfaces, representing a cancellable asynchronous computation. It can be used to wrap Callable or Runnable objects and execute them in a thread.

Key features:

• Runnable: Can be passed to threads or executors for execution.
• Future: Allows obtaining the computation result, checking its status (isDone()), cancelling (cancel()), and blocking until completion (get()).
• Flexibility: Can be used both for wrapping existing Runnable and for executing operations that return a result (Callable).

Example usage:

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;
import java.util.concurrent.ExecutionException;

// Task that returns a result
Callable<Integer> myCallable = () -> {
    // Perform a long operation
    Thread.sleep(1000);
    return 42;
};

// Wrap Callable in FutureTask
FutureTask<Integer> futureTask = new FutureTask<>(myCallable);

// Create a thread to execute the task
Thread thread = new Thread(futureTask);

// Start the thread
thread.start();

try {
    // Get the result (blocks until completion)
    Integer result = futureTask.get();
    System.out.println("Result: " + result); // Result: 42
} catch (InterruptedException | ExecutionException e) {
    e.printStackTrace();
}

// Check status
System.out.println("Task completed: " + futureTask.isDone()); // Task completed: true