using java reflection to disable methods

If your class is also serializable, the interaction between construction, deserialization, and finalization turns this headache into a nightmare.Īnd even if you get all of it right, subclasses can easily make this house of cards collapse if not coded with equal care.Īnd that doesn't even take malice into account.įinalizers have no restrictions on them, so if they manage to add a reference to the object that's being finalized to somewhere reachable, the object can't be collected after all - it's resurrected! That means when writing a finalizer, you're automatically in a multi-threaded situation where you can't rely on much around you. Which threads handle finalization and in which order are objects finalized?īoth is unspecified and can't be controlled. Other weasely behavior comes from words not said: Your app needs resources in sudden spikes and during those phases you acquire resources faster than the GC gets around to collecting them.Īgain, you may run out just because releasing resources is arbitrarily delayed. You could be running out of file handles or web sockets even though you don't use them any more, just because they're not yet released.

So all your unused-but-not-yet-closed resources hang out in the old generation, ready to be closed during finalization, but the GC isn't in any rush to do that because its concern is heap memory, which you still have plenty of. Say your app launched and went through the initial churn and now the old generation only grows very slowly, which means the GC only processes it very rarely.Īnd lets assume your resource-handling objects are usually tenured into the old generation before becoming unreachable. The GC will call the finalizer at some point in the future. If an instance of that class become unreachable, the GC will figure that out and schedule to call the finalize method at some point before it reclaims the object's memory. So let's take these two mostly unrelated responsibilities and mix'em up really good, nothing bad ever came from that.Ī class that handles a resource, say web sockets, will implement the protected method finalize - called a finalizer - and therein close all resources. When nobody references the instance that holds the resource.Īnd, oh how handy, the garbage collector knows when that's the case! How can you be sure that nobody's using it any more? So how do you know when you can release a resource? It's not very good at that, but more on that later. It is intended to let us avoid resource leaks like amassing and never releasing file handles until the file system won't hand out any more or not releasing off-heap memory until it runs out. what is it, what are its problems, and what's going to happen now, meaning probably in Java 18?įinalization has been with Java from day one. I'm Nicolai Parlog, Java developer advocate at Oracle and today we're gonna talk about finalization and then later a tiny bit about reflection. Welcome everyone, to the Inside Java Newscast where we cover recent developments in the OpenJDK community. I would never play such cheap tricks on you. Is it to give you a reason to stick with me through a topic that could otherwise be considered somewhat boring? It gives me a deeper understanding of Java as a whole that goes way beyond that one thing. That every time something new comes or something old goes, I don't just learn about that thing, but also about Java's history or its internals, about why it is the way it is and why that's not as good as it could be. Well, that Java gets better and better obviously, but right after that?

You know what I like best about observing Java evolve?

Using java reflection to disable methods