Dear Joshua, In example class `Intern` and method `intern` is race condition between line 18 and 19. It can also lead to memory leak. https://github.com/jbloch/effective-java-3e-source-code/blob/bdc828a7af2bdfac28e3c38bd7d1a2ae05736ccc/src/effectivejava/chapter11/item81/Intern.java#L19 Kindly regards, Marcin PS Thank you for your book. I'm continuously learning new things from it.