Question

I implemented a Runnable and it checks correct if a boolean value turns true.

But i want to return this value to my class where i start the Thread.

I noticed that i can return a value with Future Callables, with them i can just calculate something and return it immediatly but i cant check permanently if the value turns true.

How can i achieve this?

Thank you for your help.

public class ResultChecker implements Runnable{
    private DrawView drawView;

    public ResultChecker(DrawView drawView){
        this.drawView = drawView;
    }

    public void run() {
        boolean run = true;
        while(run){
            if(drawView.isNextQuestion()){
                //RETURN VALUE HERE
                run = false;
            }
        }
    }

}

Answer 1

If you want to poll, then create a method in ResultChecker that can be called by the thread that wants the return value.

public class ResultChecker implements Runnable{
    private DrawView drawView;
    private volatile Result r;

    public ResultChecker(DrawView drawView){
        this.drawView = drawView;
        this.r = null;
    }

    public Result poll() {
        return r;
    }

    public void run() {
        boolean run = true;
        while(run){
            if(drawView.isNextQuestion()){
                //RETURN VALUE HERE
                r = someObject;
                // once r has been assigned, you cannot touch it again
                // or the object it refers to from this thread because
                // there are no locks
                run = false;
            }
        }
    }

}

The poller will poll like this:

r = resultChecker.poll();
if(r != null) {
    // we have result
} else {
    // result is not ready
    // try again later
}

If you want to return multiple values, you will have to extend this a bit with a queue.