How to implement multithreading with a return value?

Question

I have been working on a calculator app in Java and I want to implement multithreading for this. I want to start a second thread, to calculate the answer for the given input. The only problem is, the calculation has to return a value and that value need to get displayed, but I don't know how to handle that. (I know its kind of useless to implement multithreading because the calculation doesn't even take a second, but I want to do it as practice and see if its possible)

Here you can see the code for which I want to start a second thread for:

public String calculate() {
//The input (StringBuilder) gets converted to an ArrayList
        String[] tmpArray = inputAsText.toString().split(" ");
        inputAsArrayList = new ArrayList(Arrays.asList(tmpArray));

//Other functions are called to perform calculations on
        inputAsArrayList = calculateFor("x", "÷");
        inputAsArrayList = calculateFor("+", "-");

//The answer gets retrieved from the arrarList and returned as a String
        String answer = String.valueOf(inputAsArrayList.get(0));
        clearInput();
        return answer;
    }

Rob Spoor · Accepted Answer · 2022-02-11 10:22:59Z

1

There are two ways to deal with results from asynchronous code:

Wait for the response to become available. This makes the results become available in the current thread.
Use some kind of callback mechanism. The results are still not available in the current thread.

The waiting can be done using Future and one of its get methods. For callbacks, I prefer CompletableFuture, with methods like thenAccept. You can even easily hook it into something like the Swing/AWT Event Dispatcher:

future.thenAcceptAsync(action, EventQueue::invokeLater);

This works because the second argument needs to be an Executor, which is a functional interface with one method that takes a Runnable and returns nothing. That's exactly what EventQueue.invokeLater is.

answered Feb 11, 2022 at 10:22

Rob Spoor

9,9641 gold badge28 silver badges29 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to implement multithreading with a return value?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related