How FutureTask Works in Java

FutureTask is a class in Java used for asynchronously executing tasks, and its working principle can be summarized simply in the following steps:

1. Create a FutureTask object and pass a Callable or Runnable task as a parameter.
2. Use the get() method of FutureTask to retrieve the result of the task execution. If the task is not yet completed, the get() method will block the current thread until the task is finished and returns the result.
3. When the get() method is called, it will immediately return the result if the task is already completed; if the task is not yet completed, the get() method will wait for the task to be completed and then return the result.
4. If the task has already been completed, calling the get() method again will immediately return the result without executing the task again. This helps prevent repetitive task execution.
5. FutureTask also provides a cancel() method to stop the execution of a task. If the task is canceled, calling the get() method again will throw a CancellationException.

In summary, the working principle of FutureTask is to encapsulate an asynchronously executed task and provide methods to retrieve the task’s result and cancel the task’s execution. By utilizing internal threads and synchronization mechanisms, it achieves the functionality of blocking to obtain results when the task is not yet completed.