When is finalize called

Generally an object becomes eligible for garbage collection in Java on following cases:. This method is called when the object becomes eligible for GC.

There are many situations where the objects may not be garbage collected. Sometimes when it is destroyed, an object must make an action. For example, if an object has a non-java resource such as a file handle or a font, you can verify that these resources are released before destroying an object.

To manage such situations, java offers a mechanism called "finalizing". By finalizing it, you can define specific actions that occur when an object is about to be removed from the garbage collector.

To add a finalizer to a class simply define the finalize method. Java execution time calls this method whenever it is about to delete an object of that class. Within the finalize method you specify actions to be performed before destroying an object.

The garbage collector is periodically searched for objects that no longer refer to any running state or indirectly any other object with reference. Before an asset is released, the Java runtime calls the finalize method on the object. The finalize method has the following general form:. With the protected keyword, access to finalize by code outside its class is prevented.

It is important to understand that finalize is called just just before the garbage collection. It is not called when an object leaves the scope, for example. It means you can not know when, or if, finalize will be executed. As a result, the program must provide other means to free system resources or other resources used by the object. You should not rely on finalize for normal running of the program. If the garbage collector fails to collect the object and tries to run it again, the method doesn't get called in the second time.

Just keep in mind that it might not get called and that it definitely won't be called twice. The finalize method could run zero or one time. In the following code, finalize method produces no output when we run it since the program exits before there is any need to run the garbage collector.

It is not called when an object goes out of scope. This means that you cannot know when or even if finalize will be executed. If your program end before garbage collector occur, then finalize will not execute.

Therefore, it should be used as backup procedure to ensure the proper handling of other resources, or for special use applications, not as the means that your program uses in its normal operation. There is no fixed time at which finalizers must be executed because time of execution depends on the Java Virtual Machine JVM.

The only guarantee is that any finalizer method that executes will do so sometime after the associated object has become unreachable detected during the first cycle of garbage collection and sometime before the garbage collector reclaims the associated object's storage during the garbage collector's second cycle.

Execution of an object's finalizer may be delayed for an arbitrarily long time after the object becomes unreachable. Consequently, invoking time-critical functionality such as closing file handles in an object's finalize method is problematic. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. When is the finalize method called in Java? Ask Question. Asked 11 years, 7 months ago. Active 11 months ago. Viewed k times. Improve this question. Chris Martin Just as a side note: finalize is marked as deprecated in Java 9 — Reg.

It's deprecated starting Java9. Add a comment. Active Oldest Votes. Improve this answer. Joachim Sauer Joachim Sauer k 55 55 gold badges silver badges bronze badges. It's not a "life span" issue.

You can put your program in an infinite loop for years , and if the garbage collector is not needed it will never run. VikasVerma: the perfect replacement is nothing: you should not need them.

In those cases the Closable interface and the idea behind it is probably what you want: make. You might want to add a finalize method "just to be save", but that would be more of a debugging tool than an actual fix because it's not reliable enough. Dragonborn: that's actually a quite different question and should be asked separately. There are shutdown hooks, but they are not guaranteed if the JVM shuts down unexpectedly a. But their guarantees are significantly stronger than those for finalizers and they are safer as well.

Your last paragraph says to use it only for cleaning up resources even though there is no guarantee it will ever be called. Is this optimism speaking? I would assume that something unreliable as this wouldn't be suited for cleaning up resources either.

Finalizers can sometimes save the day I had a case where a 3rd party library was using a FileInputStream, never closing it. My code was calling the library's code, and then tried to move the file, failing because it was still open. I had to force call System. Show 7 more comments. 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.

Paul Bellora Also note that the C example provides a destructor instead of overriding the Finalize method. For an additional example that overrides the Finalize method, see the GC. SuppressFinalize method. The Finalize method is used to perform cleanup operations on unmanaged resources held by the current object before the object is destroyed.

The method is protected and therefore is accessible only through this class or through a derived class. The Object class provides no implementation for the Finalize method, and the garbage collector does not mark types derived from Object for finalization unless they override the Finalize method. If a type does override the Finalize method, the garbage collector adds an entry for each instance of the type to an internal structure called the finalization queue.

The finalization queue contains entries for all the objects in the managed heap whose finalization code must run before the garbage collector can reclaim their memory. The garbage collector then calls the Finalize method automatically under the following conditions:. After the garbage collector has discovered that an object is inaccessible, unless the object has been exempted from finalization by a call to the GC. NET Framework only , during shutdown of an application domain, unless the object is exempt from finalization.

During shutdown, even objects that are still accessible are finalized. Finalize is automatically called only once on a given instance, unless the object is re-registered by using a mechanism such as GC. SuppressFinalize method has not been subsequently called. Finalize operations have the following limitations:. The exact time when the finalizer executes is undefined. To ensure deterministic release of resources for instances of your class, implement a Close method or provide a IDisposable.

Dispose implementation. The finalizers of two objects are not guaranteed to run in any specific order, even if one object refers to the other. That is, if Object A has a reference to Object B and both have finalizers, Object B might have already been finalized when the finalizer of Object A starts. The Finalize method might not run to completion or might not run at all under the following exceptional circumstances:. If another finalizer blocks indefinitely goes into an infinite loop, tries to obtain a lock it can never obtain, and so on.

Because the runtime tries to run finalizers to completion, other finalizers might not be called if a finalizer blocks indefinitely. If the process terminates without giving the runtime a chance to clean up. The runtime continues to finalize objects during shutdown only while the number of finalizable objects continues to decrease.

This behavior ensures process integrity if the finalizer cannot free or destroy resources. You should override Finalize for a class that uses unmanaged resources, such as file handles or database connections that must be released when the managed object that uses them is discarded during garbage collection.

You shouldn't implement a Finalize method for managed objects because the garbage collector releases managed resources automatically. As we know, a final block will always execute even there is an exception occurred in a try block, except System. The main difference between a static and final keyword is that static is keyword is used to define the class member that can be used independently of any object of that class. Final keyword is used to declare, a constant variable, a method which can not be overridden and a class that can not be inherited.

Static methods can be overriden, but they cannot be overriden to be non-static,Whereas final methods cannot be overridden. A final method is just a method that cannot be overridden — while static methods are implicitly final, you might also want to create an final instance method. Final cannot be overridden because that is the purpose of the keyword, something that cannot be changed or overridden.

The purpose of inheritance and polymorphism is to have objects of same class implementing methods not the names but the code in the methods in different ways. In Java final is the access modifier which can be used with a filed class and a method.

When a method if final it cannot be overridden. When a variable is final its value cannot be modified further. When a class is finale it cannot be extended. However, an abstract class can have a final method. This final method is treated like a normal method with a body which cannot be overridden. Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Social studies When Finalize method is called?

Social studies. Ben Davis November 13, When Finalize method is called? Does finalize block always run before GC? What is use of finalize method?