What is FutureTask and How to use it ?

 FutureTask

• Similar to Latch
• implements Future
• has 3 states : 
• Waiting to run, Running and Completed
• Once FutureTask completed, it cannot be restarted
• needs Callable in its constructor
• Callable is similar to Runnable used in Thread' s constructor
• Callable implements call method which is used to return the data
• Future.get() returns data [using Callable.call] if ready, otherwise waits for loading data
• Future.get() throws ExecutionException as a wrapper on any exception thrown by task code
• used by the Executor framework

Using FutureTask

1. Defining FutureTask to provide data
// Create new object FutureTask with return type as generic
// Create new Callable object (+ implement call method)
// and pass it to FutureTask constructor
FutureTask future = new FutureTask<UserInfo> (
      new Callable<UserInfo>() {
            public UserInfo call() throws UserDataException {
                  return loadData();
            }
      });

2. Start FutureTask as a thraed
// Define a thread using FutureTask
private Thread thread = new Thread(future);


// Start the thread  
public void start() { thread.start(); }


3. Get the data using FutureTask
// Call FutureTask.get to load the data
try {
     return future.get();
} catch (ExecutionException e) {
    // Hanlde it
}