Java Thread behaving synchronously

Question

in the below piece of code when ever the while loop is empty it's going in an infinite loop as the flag updated by thread 2 isn't getting reflected

public class testing2 {
    private static boolean flag = false;

    public static void main(String[] args) {
        // Thread 1: Toggles the flag value
        Thread thread1 = new Thread(() -> {
            while (!flag) {
                //System.out.println("hello");
            }
            System.out.println("Flag is now true!");
        });

        // Thread 2: Changes the flag value after a delay
        Thread thread2 = new Thread(() -> {
            try {
                Thread.sleep(1000); // Delay for 1 second
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            flag = true;
            System.out.println("Flag has been set to true.");
        });

        // Start both threads
        thread1.start();
        thread2.start();
    }
}

result : "Flag has been set to true." and continues running

but whenever i uncomment the code in while loop i'm getting below response

. . . Hello hello hello Flag has been set to true. Flag is now true!

Kindly help me understand why is it behaving like this

i was trying to reproduce an error scenario