Here is an tricky concurrency concern in Java when using Anonymous Inner Class with ExecutorService, if you use collection from outside class, that collection actually a global variable in the Inner Class, and need to take care the issues happened in concurrency access.

For this class: <pre>
public static void main(String[] args) throws InterruptedException {
  ExecutorService es = Executors.newFixedThreadPool(80);
  final List<String> list = new ArrayList<String>();
  for (int i = 0; i < 100000; i++)
   es.execute(new Runnable() {
    @Override
    public void run() {
     list.add(new String());
    }
   });
  es.shutdown();
  while (true) {
   boolean terminated = es.awaitTermination(5, TimeUnit.SECONDS);
   if (terminated) {
    break;
   }
  }
  for (String string : list) {
   if (string == null)
    System.out.println("Have null");
  }
 }
 </pre>
 actually same as
<pre>
 private static final class RunnableImpl implements Runnable {
  private final List<String> mList;
  private RunnableImpl(List<String> list) {
   mList = list;
  }
 
  @Override
  public void run() {
   mList.add(new String());
  }
 }
 public static void main(String[] args) throws InterruptedException {
  ExecutorService es = Executors.newFixedThreadPool(80);
  final List<String> list = new ArrayList<String>();
  for (int i = 0; i < 100000; i++)
   es.execute(new RunnableImpl(list));
  /** @formatter:on */
  es.shutdown();
  while (true) {
   boolean terminated = es.awaitTermination(5, TimeUnit.SECONDS);
   if (terminated) {
    break;
   }
  }
  for (String string : list) {
   if (string == null)
    System.out.println("Have null");
  }
 }
</pre>