什么时候应该在java中使用finalize（）方法？

Question

When should we really use finalize() method in java?

If we want to close connection in finalize() method then it's better to use the code below as waiting for GC to call finalize() method and then release the connection does not make sense

try{
// Connection creation
}finally{
//close connection
}

So the question is does finalize() method has any relevance today?

Answer 1

It is indeed preferable to release resources by calling a method explicitly. Finalizers are not necessarily called promptly or even at all. And they add a performance penalty.

However, finalizers may still be used as a safety net to release resources, in case the client has forgotten to dispose explicitly.

From the topic "Avoid finalizers" in Joshua Bloch's "Effective Java," 2nd ed.:

[D]on't use finalizers except as a safety net or to terminate noncritical native resources. In those rare instances where you do use a finalizer, remember to invoke super.finalize. If you use a finalizer as a safety net, remember to log the invalid usage from the finalizer.

Answer 2

The only usecase I can think of for using finalize() is:

Suppose you have a static resource (member) in your class and want to do some cleanup, finalization or logging on that resource at the time of class being unloaded then you need to override finalize() method and do all that.

Answer 3

The short answer is never. Finalize() is full of subtle issues, and greatly slows garbage collections.

The longer answer is that maybe, maybe, during development, you want to check whether the important connection, file, socket or whatever was closed, and, if not, log a warning so that developers can investigate and properly fix the problem.

Answer 4

finalize() does not only release resource like socket, but also manage the memory. Theoretically speaking, you do not need to call finalize() explicitly in your code. It is performed at proper time by the VM.

Answer 5

Practically finalize() shouldnt be used especially shouldnt be used to clean up resources. If a resource is acquired it is better from the performance perspective to explicitly release the resource rather than wait for JVM to call finalize() . You cannot foresee when JVM will call finalize() and if you are done with the resource you would be holding it unnecessarily for longer. I have seen somebody nullifying variables inside the finalize method, which is another bad practice as it slows down the program by extending GC cycles, with completely unnecessary lines of codes. GC is designed to handle very well dead objects clean up process.