Why does a thread outlive the main method in Java?

Question

I was teaching myself Java threading and I noticed something that confuses me a little. I made a class called engine implementing Runnable. The r

Answer 1

The Java Language Specification section 12.8 indicates:

12.8. Program Exit

A program terminates all its activity and exits when one of two things happens:

All the threads that are not daemon threads terminate.

Some thread invokes the exit method of class Runtime or class System, and the exit operation is not forbidden by the security manager.

This means it is not enough for the main thread to finish.

If you do want it to exit when the main thread ends you need to either make the new thread a daemon by using Thread#setDaemon or use Thread#join as you initially suggested.