When is the finalize() method called in Java?

I need to know when the finalize() method is called in the JVM. I created a test class which writes into a file when the finalize() method is called by overriding it. It is not executed. Can anybody tell me the reason why it is not executing?

Solution 1:

The finalize method is called when an object is about to get garbage collected. That can be at any time after it has become eligible for garbage collection.

Note that it's entirely possible that an object never gets garbage collected (and thus finalize is never called). This can happen when the object never becomes eligible for gc (because it's reachable through the entire lifetime of the JVM) or when no garbage collection actually runs between the time the object become eligible and the time the JVM stops running (this often occurs with simple test programs).

There are ways to tell the JVM to run finalize on objects that it wasn't called on yet, but using them isn't a good idea either (the guarantees of that method aren't very strong either).

If you rely on finalize for the correct operation of your application, then you're doing something wrong. finalize should only be used for cleanup of (usually non-Java) resources. And that's exactly because the JVM doesn't guarantee that finalize is ever called on any object.

Solution 2:

In general it's best not to rely on finalize() to do any cleaning up etc.

According to the Javadoc (which it would be worth reading), it is:

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

As Joachim pointed out, this may never happen in the life of a program if the object is always accessible.

Also, the garbage collector is not guaranteed to run at any specific time. In general, what I'm trying to say is finalize() is probably not the best method to use in general unless there's something specific you need it for.