Does this "invoked" method run in a separate thread?
No, Java Reflection in general has nothing to do with multithreading.
will the child thread be properly garbage collected?
Since there is no multithreading involved, I believe your second question is rendered moot. More generally, though, there is no propagation of exceptions between threads, so if a child thread ends due to an unhandled exception, the parent thread won't be able to magically "catch" it. Think about it logically: the parent thread will at that point be off to some completely unrelated piece of code and there would be no sense in interrupting it with a stacktrace that has nothing to do with what it is executing.