像这样，我有两条线。sleeprunner线程向列表中添加一些随机数，然后将flag更改为true并休眠。主线程等待sleeprunner线程，直到sleeprunner对象中的标志从false变为true，然后主线程将中断sleeprunner线程，程序将结束。
但问题是，当while循环在主线程中没有主体代码时，变量runner不会在循环内更新，换句话说，sleeprunner线程将标志从false更改为true后，程序不会结束。所以我试着在idea中使用调试工具，但是程序结束得很顺利。如果我在主线程的while循环体中编写一些代码，比如system.out.println（）或thread.sleep（1），程序也会成功结束。太不可思议了！有人知道为什么会这样吗？谢谢。

public class Test1 {
        public static void main(String[] args) {
            SleepRunner runner = new SleepRunner();
            Thread thread = new Thread(runner);
            thread.start();
            while(!(runner.isFlag())){
                /*try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }*/
            }
            System.out.println("END");
            thread.interrupt();
        }
    }

public class SleepRunner implements Runnable {
        private boolean flag = false;

        public boolean isFlag() {
            return flag;
        }

        @Override
        public void run() {
            List<Integer> list = new ArrayList<>();
            for (int i = 0; i < 100; i++) {
                try {
                    Thread.sleep((long) (Math.random() * 200));
                }
                catch (InterruptedException e) {
                    System.out.println("Interrupted");
                }
                int num = (int) (Math.random() * 100);
                System.out.println(Thread.currentThread().getName() + " " + num);
                list.add(num);
            }

            flag = true;

            System.out.println("30 Seconds");
            try {
                Thread.sleep(30000);
            }
            catch (InterruptedException e) {
                System.out.println("Interrupted in 30 seconds");
            }
            System.out.println("sleep runner thread end");
        }
    }