What is an "incompletely constructed object"?
- by Joonas Pulakka
Goetz's Java Concurrency in Practice, page 41, mentions how this reference can escape during construction. A "don't do this" example:
public class ThisEscape {
public ThisEscape(EventSource source) {
source.registerListener(
new EventListener() {
public void onEvent(Event e) {
doSomething(e);
}
});
}
}
Here this is "escaping" via the fact that doSomething(e) refers to the enclosing ThisEscape instance. The book states:
Publishing an object from within its constructor can publish an incompletely constructed object. This is true even if the publication is the last statement in the constructor. If the this reference escapes during construction, the object is considered not properly constructed.
I don't quite get this. If the publication is the last statement in the constructor, hasn't all the constructing work been done before that? How come is this not valid by then? Apparently there's some voodoo going on after that, but what?
