Returning a value from Runnable

Question

The run method of Runnable has return type void and cannot return a value. I wonder however if there is any workaround of this.

I have a method like this:

public class Endpoint {
    public method() {
       Runnable runcls = new RunnableClass();
       runcls.run()
    }
}

The method run is like this:

public class RunnableClass implements Runnable {
    
    public JaxbResponse response;

    public void run() {
        int id = inputProxy.input(chain);
        response = outputProxy.input();
    }
}

I want to have access to response variable in method. Is this possible?

Answer 1

Use Callable<V> instead of using Runnable interface.

Example:

public static void main(String args[]) throws Exception {     ExecutorService pool = Executors.newFixedThreadPool(3);     Set<Future<Integer>> set = new HashSet<>();      for (String word : args) {       Callable<Integer> callable = new WordLengthCallable(word);       Future<Integer> future = pool.submit(callable);       set.add(future);     }      int sum = 0;     for (Future<Integer> future : set) {       sum += future.get();     }      System.out.printf("The sum of lengths is %s%n", sum);     System.exit(sum); } 

In this example, you will also need to implement the class WordLengthCallable, which implements the Callable interface.

Answer 2

public void check() {     ExecutorService executor = Executors.newSingleThreadExecutor();     Future<Integer> result = executor.submit(new Callable<Integer>() {         public Integer call() throws Exception {             return 10;         }     });      try {         int returnValue = result.get();     } catch (Exception exception) {        //handle exception     } } 

Answer 3

Have a look at the Callable class. This is usually submited via an executor service

It can return a future object which is returned when the thread completes

Answer 4

Yes, there are workaround. Just use queue and put into it value which you want to return. And take this value from another thread.

public class RunnableClass implements Runnable{

        private final BlockingQueue<jaxbResponse> queue;


        public RunnableClass(BlockingQueue<jaxbResponse> queue) {
            this.queue = queue;
        }

        public void run() {
            int id;
            id =inputProxy.input(chain);
            queue.put(outputProxy.input());
        }
    }


    public class Endpoint{
        public method_(){
            BlockingQueue<jaxbResponse> queue = new LinkedBlockingQueue<>();

            RunnableClass runcls = new RunnableClass(queue);
            runcls.run()

            jaxbResponse response = queue.take(); // waits until takes value from queue
        }
    }