Future is an interface in the Java language that is a part of the java.util.concurrent package. It serves as a symbol for the output of an asynchronous computation. The interface offers ways to determine whether a computation has finished, to wait for it to finish, and to receive the computation's result. After the task or calculation is finished, it cannot be undone. A Future interface offers ways to determine whether the computation is finished, to wait for it to finish, and to receive the computation's results. After the computation is finished, the result is retrieved using the Future's get() method, and the computation stalls until it is finished. Future and FutureTask are both included in the Java 1.5 java.util.concurrent package.
- FutureTask can be sent to an ExecutorService instance for execution because it is a concrete implementation of the Future, Runnable, and RunnableFuture interfaces.
- The ExecutorService delivers a Future that represents the task when a Callable or Runnable instance calls ExecutorService.submit(). and it can be produced manually as well.
- When invoking get(), FutureTask behaves similarly to a CountDownLatch in that it waits for the task to finish or fail.
- The task's current state determines how the parameterless get() method will behave. When a task is not finished, the get() method becomes blocked. When a job is finished, it either returns the outcome or raises an ExecutionException.
- A timeout parameter may be passed to an overloaded version of get() to restrict the thread's timeout period.
The Future interface had some flaws, including the following:
- The calculation cannot be done manually when using Future.
- Once the commutation is complete, it doesn't notify.
- It is impossible to make and combine its chain.
- Java 8 introduced CompletableFuture to get around the aforementioned restrictions.
The Future class in Java is a type of class that represents the result of an asynchronous computation. It is used in multithreaded programming to execute long-running operations in a separate thread, without blocking the main thread. The Future class has been a part of Java since version 5, and it has undergone several changes and improvements in subsequent versions. In Java 8, CompletableFuture was introduced, which extends the Future interface and provides additional features for asynchronous programming. Some of the key features of the Future class in Java include:
- Asynchronous execution: The Future class allows you to execute a long-running operation in a separate thread, without blocking the main thread. You can submit a task to an ExecutorService and receive a Future object in return.
- Non-blocking result retrieval: The Future class provides a way to retrieve the result of a computation asynchronously, without blocking the main thread. You can call the get() method on the Future object to retrieve the result, and the method will block until the result is available.
- Exception handling: The Future class allows you to handle exceptions that may occur during the execution of a task. If an exception is thrown during the execution of a task, the Future object will capture it and make it available through the get() method.
- Cancellation: The Future class allows you to cancel a task that has been submitted to an ExecutorService. We can call the cancel() method on the Future object to cancel the task, and the method will return true if the task was successfully cancelled.
- Chaining: The CompletableFuture class extends the Future interface and provides additional features for chaining multiple computations together. You can use the thenApply(), thenAccept(), and thenRun() methods to chain multiple computations together and create a pipeline of asynchronous operations.
The Future class in Java is a powerful tool for asynchronous programming. It allows you to execute long-running operations in a separate thread, retrieve results asynchronously, handle exceptions, cancel tasks, and chain multiple computations together. As Java continues to evolve, we can expect to see further improvements and enhancements to the Future class and other asynchronous programming features. The Future class also provides a way to handle exceptions that may occur during the execution of a task. When you call the get() method on a Future object, if an exception is thrown during the execution of the task, the Future object will capture it and make it available through the get() method.