Java Thread visibility problem.Why is there an infinite loop after adding output in threadA below? Isn't there a memory visibility problem? Why does t

Question

Java Thread visibility problem. Why is there an infinite loop after adding output in threadA below? Isn't there a memory visibility problem? Why does the threadA get the latest flag in 1s?

public class Test {
    private static boolean flag = true;

    public static void main(String[] args) throws InterruptedException {
        new Thread(() -> {
            while (flag) {
                //If you don't add this sout, it will be an infinite loop, 
                //and if you add it, it will not be an infinite loop.
                System.out.println("loop");
            }
            System.out.println("end");
        },"threadA").start();

        TimeUnit.MILLISECONDS.sleep(1000);

        flag = false;
    }
}