Returning value from Thread

java android multithreading
Neeta picture Neeta · Feb 5, 2012 · Viewed 210.3k times · Source

I have a method with a HandlerThread. A value gets changed inside the Thread and I'd like to return it to the test() method. Is there a way to do this?

public void test()
{   
    Thread uiThread = new HandlerThread("UIHandler"){
        public synchronized void run(){
            int value; 
            value = 2; //To be returned to test()
        }
    };
    uiThread.start();
}

Answer

Johan Sjöberg picture Johan Sjöberg · Feb 5, 2012

Usually you would do it something like this

 public class Foo implements Runnable {
     private volatile int value;

     @Override
     public void run() {
        value = 2;
     }

     public int getValue() {
         return value;
     }
 }

Then you can create the thread and retrieve the value (given that the value has been set)

Foo foo = new Foo();
Thread thread = new Thread(foo);
thread.start();
thread.join();
int value = foo.getValue();

tl;dr a thread cannot return a value (at least not without a callback mechanism). You should reference a thread like an ordinary class and ask for the value.

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