Question

I have two ListenableFutures which are completed on other threads. Each future is of a different type, and I wish to use both of their results when they are both complete.

Is there an elegant way to handle this using Guava?

Answer 1

Runnable listener = new Runnable() {
    private boolean jobDone = false;

    @Override
    public synchronized void run() {
        if (jobDone || !(future1.isDone() && future2.isDone())) {
            return;
        }
        jobDone = true;
        // TODO do your job
    }
};
future1.addListener(listener);
future2.addListener(listener);

Not really elegant, but should do the job.

Or, more elegant, but you’ll need casts:

ListenableFuture<List<Object>> composedFuture = 
    Futures.allAsList(future1, future2);