multithreading - Java: starting a new thread in a constructor

Question

Why is starting a new thread in a constructor frowned upon in Java (or anywhere, for that matter). I'm getting warnings from Netbeans for doing so, but it isn't giving me any refactoring suggestions. I'm writing a client/server Swing application, and the thread I'm starting is in the server's JFrame constructor, in order to continuously listen for client datagrams.

Why is this not good practice and how should I avoid it?

Answer 1

Starting a thread from the constructor lets the started thread access the object being constructed before it's properly constructed, and thus makes a not completely constructed object available to the new thread.

You could create the thread in the constructor, and provide a "startup" method to start the thread from the outside.

Or you could make the constructor and startup methods private and provide a static factory method which would create the object, start the thread, and return the created object.