It can be used instead of coroutines in small projects

ApplicationExecutors.java

public class ApplicationExecutors {

    private final Executor background;
    private final Executor mainThread;

    public Executor getBackground() {
        return background;
    }

    public Executor getMainThread() {
        return mainThread;
    }

    public ApplicationExecutors() {
        this.background = Executors.newSingleThreadExecutor();
        this.mainThread = new MainThreadExecutor();
    }

    private static class MainThreadExecutor implements Executor {
        private Handler mainThreadHandler = new Handler(
                       Looper.getMainLooper()
        );

        @Override
        public void execute(Runnable command) {
            mainThreadHandler.post(command);
        }
    }
}