code: private List<ActivityStartListener> getActivityStartListeners(
              Class<? extends Activity> activityClass) {
          List<ActivityStartListener> result =
                  this.activityStartListeners.get(activityClass);
          if (result == null) {
              result = new ArrayList<ActivityStartListener>();
              this.activityStartListeners.put(activityClass, result);
          }
          return result;
      }
docs: /*
  Not synchronized, do that in the caller code.