code: private void setCurActivity(Activity curActivity) {
          synchronized (LOCK_LASTACTIVITIES) {
              int idxCurActivity = curActivities.indexOf(curActivity);
              if (idxCurActivity == -1) {
                  curActivities.add(curActivity);
              } else if (idxCurActivity < curActivities.size()-1){
                  curActivities.remove(curActivity);
                  curActivities.add(curActivity);
              }
          }
      }
docs: 设置最新的activity | Set up the latest activity
  @param curActivity 最新的activity | Latest activity