This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Because they apply to the current thread. Certainly you wouldn't want just any thread to call sleep() or yield() on your thread. And you probably wouldn't want another thread to be able to clear your current thread's interrupted flag.