Why HotSpot will optimize the following using hoisting?

Question

In the \"Effective Java\", the author mentioned that

while (!done) i++;

can be optimized by HotSpot into

if (!done) {
             


        

Answer 1

If you add System.out.println("i = " + i); in the while loop. The hoisting won't work, meaning the program stops as expected. The println method is thread safe so that the jvm can not optimize the code segment?