Need help returning object in thread run method

There are several solutions to this problem:

• Use an data structure external to the Thread. Pass the object in your constructor and update it, when your Thread is about to finish.

• Use a callback method. When your Thread finishes, call the callback.

• Make use of a java.util.concurrent.Future (Java >= 1.5):

  A Future represents the result of an asynchronous computation. Methods are provided to check if the computation is complete, to wait for its completion, and to retrieve the result of the computation.

Let it implement Callable<T> instead of Thread or Runnable. Here T must represent the type of the result. Use ExecutorService to execute it. It will return the result in flavor of a Future<V>.

Here's an SSCCE with String as T, just copy'n'paste'n'run it.

package com.stackoverflow.q2300433;import java.util.Arrays;import java.util.List;import java.util.concurrent.Callable;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;public class Test {    public static void main(String... args) throws Exception {        ExecutorService executor = Executors.newSingleThreadExecutor();        Future<String> future = executor.submit(new Task());        System.out.println(future.get()); // Prints "result" after 2 secs.        // Or if you have multiple tasks.        // List<Future<String>> futures = executor.invokeAll(Arrays.asList(new Task()));        // for (Future<String> future : futures) {        //     System.out.println(future.get());        // }        executor.shutdown(); // Important!    }}class Task implements Callable<String> {    public String call() throws Exception {        Thread.sleep(2000);        return "result";    }}