56.12 Working with Callable Tasks and Futures

As previously mentioned, the ExecutorService supports so called “Callable” tasks which are able to return a result after the task is completed. Tasks running on separate thread are typically expected to take some time to complete (otherwise they probably would not need to run on a separate thread in the first place). This raises the question of how the result is returned to the code in the thread from which the task was launched. This is achieved using the Future value type which represents a value which will be provided at some point in the future.

When a callable task is executed it returns a Future instance which may then be used by the app to obtain the result when the task completes. To see this in action, begin by editing the activity_main.xml file to add an additional button labeled “Status” with the onClick property configured to call method named statusClick:

Figure 56-3

Next, modify the...