Question

I have two threads: the main thread and a thread started from the main thread.

When the main thread exits, will the whole program terminate?

Answer 1

No.

Java programs terminate when all non-daemon threads finish.

The documentation states:

When a Java Virtual Machine starts up,
there is usually a single non-daemon
thread (which typically calls the
method named main of some designated
class). The Java Virtual Machine
continues to execute threads until
either of the following occurs:

• The exit method of class Runtime has been called and the
  security manager has permitted the
  exit operation to take place.
• All threads that are not daemon threads have died, either by returning
  from the call to the run method or
  by throwing an exception that
  propagates beyond the run method.

If you don’t want the runtime to wait for a thread, call the setDaemon method.