Bdtjtk

I've tried to get a String from the request function and add it to the lastList ArrayList, but it will not be added normally.

In this case, how can I add?

As a global variable public ArrayList lastList = new ArrayList <> (); But it did not work.

Thread thread = new Thread(new Runnable() {

        @Override

        public void run() {

            Log.d(MainActivity.TAG, "Task runned.");

            for (int i = 0; i < alarmList.size(); i++) {

                final String str = alarmList.get(i).split("#!%~#");

                for (int j = 0; j <= 8; j++) {

                    try {

                        final String output = AddActivity.request(str[1], str[2]);

                        handler.post(new Runnable() {

                            public void run() {

                                if (Integer.parseInt(str[3]) == Integer.parseInt(StringUtils.substringBetween(output, str[1] + " ", "화"))) {

                                    lastList.add(output);

                                }

                            }

                        });

                        Log.d(MainActivity.TAG, "OK");

                        break;

                    } catch (Exception ex) {

                        Log.d(MainActivity.TAG, "Exception.");

                    }

                }

            }

        }

    });

    thread.start();

    try {

        thread.join();



        Log.d(MainActivity.TAG, "thread end.");

        Log.d(MainActivity.TAG, "Size: " + lastList.size()); // Size: 0

        }

I expect the output of Size: 1, but the actual output is Size: 0.

Not sure what is handler in your code, but seems like it makes http POST and then callback is executed in another thread after POST response. So, as I understand, you are making join on the thread thread, but you are updating the list in another thread which is executed in POST callback. Since http call normally takes much longer then executing several lines of code, you don't see your list updated. To be sure - try to put Tread.sleep(10000) after thread.join(); and check if the size is 1. Also, putting some debug log statements would be really helpful here, put some log line after this lastList.add(output), so you can see the sequence of execution.

Then you can, probably, fix it by making join on your callback thread as well.

Just to demonstrate the idea I came up with this test code:

static Thread innerThread;

static ArrayList lastList = new ArrayList<>();



public static void main(String args) {

  System.out.println("Thread main: started.");



  Thread thread = new Thread(new Runnable() {

    @Override

    public void run() {

      System.out.println("Thread thread: started.");



      innerThread = new Thread(new Runnable() {

        public void run() {

          System.out.println("Thread innerThread: started.");

          try {

            System.out.println("Thread innerThread: sleeping for 1 second.");

            Thread.sleep(1000);

          } catch (InterruptedException e) {

            e.printStackTrace();

          }

          lastList.add("test");

          System.out.println("Thread innerThread: value added to the lastList");

          System.out.println("Thread innerThread: ended.");

        }

      });

      innerThread.start();

      System.out.println("Thread thread: ended.");

    }

  });



  thread.start();

  try {

    thread.join(); // to be sure that thread is finished - innerTread is initialized

    innerThread.join(); // to be sure that innerTread is finished - lastList is updated



    System.out.println("Thread main: lastList.size() = " + lastList.size()); // Size: 1

  } catch (Exception e){

    e.printStackTrace();

  }

  System.out.println("Thread main: ended.");

}

Output:

Thread main: started.

Thread thread: started.

Thread thread: ended.

Thread innerThread: started.

Thread innerThread: sleeping for 1 second.

Thread innerThread: value added to the lastList

Thread innerThread: ended.

Thread main: lastList.size() = 1

Thread main: ended.

Hope this will help!

The problem is that:

 handler.post(new Runnable() {

makes your:

 lastList.add(output);

execute after your logging:

 Log.d(MainActivity.TAG, "Size: " + lastList.size()); // Size: 0

From your code its not clear why you need to use handler.post, its mostly used when you need to update UI widgets from worker thread.