Finalize（）清理与垃圾收集器从内存中删除对象

Question

I was reading about the finalize() method and was curious:

What is the difference between the task of cleaning up objects ( setting them to NULL ) in finalize, and removing an object from memory?

Answer 1

What is the difference between the task of cleaning up objects ( setting them to NULL ) in finialize

setting to null removes ONE reference to the object. if NO more references to an object exists, the garbage collector is allowed (not required) to remove the object

and removing an object from memory?

there is NO explicit way in java to remove (destroy, delete) an object. The garbage collector will do it when he likes. Especially the time from removing the last reference to remove/destroy the object is indefinite

There is NO need to set references to null in finalize method. when the garbage collector call finalize the objects and its references will gone soon anyway.

I never wrote an own finalize method during my very long java experience.

The rare occasion in which it make sense to wrote an own finalize method appear if your object is dealing with os-resources. However, in general you use standard packages for os accesss

Answer 2

You don't "clean up" an object when you set it to null , you're just setting the reference to null, consider:

Object a = new Object();
Object b = a;
a = null;
System.out.println(b);

Once an object loses all references, it will be collected on the next GC pass. Finalize is a method that gets called when this happens, and you should avoid using it .

Just don't keep extra references around and let the GC do it's job.

Answer 3

finalize() is called by garbage collector when an object has no more references. You can override it and best practice is to use it in a try-catch-finally block to free non java resources like files. Anyway if you use it this way you should also call super.finalize() to ensure class hierarchy finalization.

This method is always for advanced use and shouldn't be used in normal production code. Free your resources in finally clauses in methods using those resources.