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.
You see, the currentThread (main thread) is being passed to the createThread method. Inside createThred method a new thread t2 is created. The run method of t2 is implemented such as it waits for thread t1 to finish, because of t1.join statement. The t1 actually is main thread. T2 will finish last, always. The last print statement in T2 is 12.