How to return Value from Multi Threading?

Question

My problem is, i just want to return value from Multi threading out of 4 threads running concurrently in Multiple times. I need a return value for every times thread calls and run. Please justify me thank you, My code snippet looking like this, Thread1: i was calling java to native library function, function returns integer value.

 public void run() {
            double time = System.currentTimeMillis();
            println("Thread-1 starts " + time);
            ED emot = new ED();
            emot.edetect("str");
            try {
              Thread.sleep(1);
            } catch {

            }
            println("Value: " + emot.getvalue);
            i = emot.getvalue;
                }

so you want to return the i at the end? where do you want to use that value? — stinepike, Oct 12 '15 at 04:36
@SinePike yes i want to use that ' i 'value for another class but thread running multiple times — VijayRagavan, Oct 12 '15 at 04:45

akhil_mittal · Answer 1 · 2015-10-12T04:56:54.173

As far as I got your problem you have 4 threads which return some value after computation. Here are few ideas:

If your thread returns some result use Callable<V> else Runnable.
You can use ExecutorService to submit your task (thread) and will get Future<V> or Future<?> depending on whether it is Callable or Runnable.
If you want to receive result of all the threads you can submit all and get futures and then invoke future.get which blocks until result is received. If you want to receive result from any of the threads then in that case you can also use ExecutorCompletionService as well which maintains a queue of results in whatever order they are received.

score 1 · Accepted Answer · edited Mar 14 '17 at 01:53

In multi threaded environment, we can return the values from thread by using Executer Service. This feature is available from JDK 5.

http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Callable.html

Example :

public class MyThread implements Callable{

    @Override
    public String call(){
        Thread.sleep(2000);
        return "Hello";
    }

    public static void main(String args[]){
          ExecutorService executor = Executors.newFixedThreadPool(5);
          Callable<String> callable = new MyThread();
          String value = executor.submit(callable);
          System.out.println("The returned value is : "+value);
          executor.shutdown();
    }

}

This is the way you can return the values from thread.

score -1 · Answer 3 · answered Oct 12 '15 at 04:54

You could make that object, emot, a class variable. This way, when you make the new object in your main thread, you could access that value through a getter method.

public static void main(String[] args) {
    //Your code

    YourRunnableClass r = new YourRunnableClass();
    Thread yourThread = r;
    yourThread.start();

    //other code

    r.getValue() //The value you are trying to get
}

public class YourRunnableClass implements Runnable {

    private ED emot;

    public int getValue() {
        return emot.getvalue();
    }

    public void run() {
        //Your Code
    }
}

Iam not able to assign YourRunnableClass r = new YourRunnableClass(); Thread yourThread = r; Type mismatch cannot convert from YourRunnableClass to Thread — VijayRagavan, Oct 12 '15 at 05:29

How to return Value from Multi Threading?

3 Answers3