如何等待异步任务完成其工作然后执行下一个语句而不冻结UI

Question

        RetrieveBusStoppage retrieveBusStoppage = new RetrieveBusStoppage();
        retrieveBusStoppage.executeOnExecutor(retrieveBusStoppage.THREAD_POOL_EXECUTOR,classes[i], Integer.toString(i));
        //retrieveBusStoppage.execute(classes[i], Integer.toString(i));  // Retrieving stoppages of bus one by one

        for(int j=0;j<busstoppage.get(i).size();j++) {

            if (source.equalsIgnoreCase(busstoppage.get(i).get(j).toString())) {
                 Toast.makeText(getApplicationContext(),"UP", Toast.LENGTH_LONG).show();
                result = "up";
                break;
            }
            if (destination.equalsIgnoreCase(busstoppage.get(i).get(j).toString())) {
                 Toast.makeText(getApplicationContext(),"DOWN", Toast.LENGTH_LONG).show();
                result = "down";
                break;
            }
        }

我希望retrieveBusStoppage完全完成然后执行for循环，因为在retrieveBusStoppage中我从数据库中检索busstoppage的值。但在此，它正在执行for循环而不完成retrieveBusStoppage.execute调用。这就是为什么bustoppage的值显示为零，因为数据库中的值未保存在其中。