Object Finalizers
Java provides two object finalizers: the finalize method on Object and the Cleaner class introduced in Java 9 under java.lang.ref.
Both run when the JVM performs garbage collection.
However, finalize is deprecated in Java 9, and Cleaner is also discouraged.
Here is why.
Why You Should Avoid Them
You cannot guarantee the execution time. Like finalize, Cleaner does not guarantee when it runs.
It may never run. Even if you accept delays, abnormal termination can prevent it from running at all. So do not rely on it for anything that must happen.
It can backfire. When an object becomes unreachable, the finalizer is queued and executed later.
If finalize runs slowly, object reclamation slows down and can trigger OutOfMemory.
It is slow. Releasing resources with AutoCloseable and try-with-resources costs about 12ns,
while garbage collection with finalizers costs about 550ns.
It is a security risk. If you override finalize and make it slow, you can degrade the system.
Because it can be overridden, the method should be marked final to prevent malicious subclasses.
Why Use It At All?
Finalizers can release native resources that the garbage collector does not manage. Because these are not Java objects, the GC does not reclaim them. Calling a finalizer can release them.
Effective Java also notes that finalizers can serve as a safety net when developers forget to call close.
Personally, I still question whether calling finalize is better than forgetting close.
If you need cleanup, implement AutoCloseable and use try-with-resources,
or implement close and invoke it explicitly.