CODEWITHSUNDEEP
javamultithreadingmethodsconcurrencyexecutorservice
Vikram
Vikram

Reputation: 2072

How to return two different types of values from a method?

I need to return two different types of variables (Future , ExecutorService) from a method. How can I move along?? here is the piece of code.. I have a class A and I m trying to call the run() method in 'B' class. 'startExecutorService' is the method which starts the threadExecutor and 'stopExecutorService' is the method which stops the threadExecutor

 public class A{
    public static void main(String[] args){

        A AObj= new A();

        Future<?> task = null;
        ExecutorService threadexec = null;

        task = AObj.startExecutorService(task, threadexec);

        AObj.stopExecutorService(task, threadexec);

    }

    public Future<?> startExecutorService(Future<?> control, ExecutorService threadExecutor){

        //'noOfThreads' determines the total no of threads to be created in threadpool
        int noOfThreads = 1;  

        // Creating an object for class 'B' which has the run() method
        B ThreadTaskOne   = new ExecutorServiceThreadClass();

        // Calling the ExecutorService to create Threadpool with specified number of threads
        threadExecutor = Executors.newFixedThreadPool(noOfThreads);

        // Creating a Future object 'control' and thereby starting the thread 'ThreadTaskOne' 
         control = threadExecutor.submit(ThreadTaskOne);    

         return control;
    }

    public void stopExecutorService(Future<?> task, ExecutorService threadExecutor){

        // Interrupting the thread created by threadExecutor
        task.cancel(true);

        if(task.isCancelled()){
            System.out.println("Task has been cancelled !!");
        }

        // Closing the threadExecutor
        threadExecutor.shutdownNow();

    }

}

I m getting ' NullPointerException' at 'stopExecutorService' method in line 'threadExecutor.shutdownNow();'The reason for this error is because, the threadExecutor value is unchanged in main method.. it has changed only in 'startExecutorService' method. So I want to return the changed value of threadExecutor back to main method, along with the Future..

Kindly help me out

Upvotes: 0

Views: 209

Answers (1)

Aniket Inge
Aniket Inge

Reputation: 25725

Make a composite class and return an object of that class?

class A{
}

class B{
}

class Composite{
  A varA;
  B varB;
  public Composite(A ax, B by){ varA = ax; varB = by;}
  public A returnA(){ return varA;}
  public B returnB(){ return varB;}
}

class Executor{
    A a;
    B b;
 ////// code here 
    public Composite returnComposite{
     Composite c = new Composite(a,b);
     return c;
  }
}

Upvotes: 2

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