主线程等待多个子线程执行完才开始工作的两种实现方式

用 join 实现

 public void testJoinOne(){
        List<StudentThread>list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            StudentThread thread = new StudentThread(i);
            list.add(thread);
            thread.start();
        }

        TeacherThread t = new TeacherThread(list);
        t.start();
    }

    // leader 在等待组员都完成任务
    private class TeacherThread extends Thread{
        List<StudentThread>list;

        public TeacherThread(List<StudentThread> list) {
            super();
            this.list = list;
        }

        @Override
        public void run() {
            super.run();
            for(StudentThread thread:list){
                try {
                    thread.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            SystemClock.sleep(1000);
            Log.d(TAG, "run: 老师干活");
        }
    }

    //工作者在执行任务
    private class StudentThread extends Thread{
        int i;

        public StudentThread(int i) {
            super();
            this.i = i;
        }

        @Override
        public void run() {
            super.run();
            SystemClock.sleep(1000);
            Log.d(TAG, "学生完成任务 "+i);
        }
    }

使用 CountDownLatch 实现

     final CountDownLatch countDownLatch = new CountDownLatch(8);

    private void testCountDown() {

        for (int i = 1; i <= 10; i++) {
            new WorkerThread(i).start();
        }
        new LeaderThread().start();

    }
    
    // leader 在等待组员都完成任务
    private class LeaderThread extends Thread{
        @Override
        public void run() {
            super.run();
            try {
                countDownLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Log.d(TAG, "run: 报告老板 Android 组的作业已经全部完成");
        }
    }

    //工作者在执行任务
    private class WorkerThread extends Thread{
        int i;

        public WorkerThread(int i) {
            super();
            this.i = i;
        }

        @Override
        public void run() {
            super.run();
            SystemClock.sleep(1000);
            countDownLatch.countDown();
            Log.d(TAG, "完成任务 "+i +" current latch is "+  countDownLatch.toString());
        }
    }

The issue contains Java and Android thread examples but does not identify a target file, test, or requested change. First determine whether the examples are intended for a blog article and clarify the desired correction or addition; done should be defined against that agreed scope.