How can a Thread return a value after finishing its job?

Question

Let's say we have this simple example:

public Example extends Thread{      String temp;          public Example(){     }      @Override     public void run(){         .         .         .         .         temp = "a_value";     }      public static void main(String[] args) {          Example th = new Example();         th.start();     }  } 

How can the Thread after finishing its job return me the String temp?

Answer 1

Make use of the (relatively) new Callable<T> instead of Runnable (available in 1.5 and newer versions):

Here is a (simple) example:

import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future;   public class Main {      public static void main(final String[] argv) {         final ExecutorService service;         final Future<String>  task;          service = Executors.newFixedThreadPool(1);                 task    = service.submit(new Foo());          try {             final String str;              // waits the 10 seconds for the Callable.call to finish.             str = task.get(); // this raises ExecutionException if thread dies             System.out.println(str);         } catch(final InterruptedException ex) {             ex.printStackTrace();         } catch(final ExecutionException ex) {             ex.printStackTrace();         }          service.shutdownNow();     } }  class Foo implements Callable<String> {     public String call() {         try {             // sleep for 10 seconds             Thread.sleep(10 * 1000);         } catch(final InterruptedException ex) {             ex.printStackTrace();         }          return ("Hello, World!");     } }