a doubt on garbage collection.

[Ajit Amitav Das]

Hi Ranchers
I got a doubt in the question given below.
Question :
If the finalize() method of an object is re-references an object so that it becomes in-eligible for garbage collection

1.The compiler will throw an error.
2.The garbage collector "collects" the object anyway.
3.The garbage collector does not collect the object in the present sweep. But when the object becomes eligible for garbage collection again, its finalize method will not be called by the garbage collector (i.e., if the garbage collector gets a chance to run.). It will simply be garbage collected.
4.The object can never be garbage collected and hence leads to memory-leak. Each time the garbage collector calls finalize before "collecting" the object the object "resurrects" itself.

To me i thinks it's option-4 but actual answer is given option-3 , is grabage collector behave like that way in those situations.

[Pradeep Kadambar]

Hi Ajit,

If you go through the Java Docs for finalize() you will find explanation for the answer being (c).

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

[Ajit Amitav Das]

thanks pradeep, thanks a lot.

[Anvi Dixit]

Hi ajit

well i didnt got the question .

If the finalize() method of an object is re-references an object so that it becomes in-eligible for garbage collection

what does 're-refrences an object' means .

Thanking you in advance

[Henry Wong]

Originally posted by Anvi Dixit:
Hi ajit

well i didnt got the question .

If the finalize() method of an object is re-references an object so that it becomes in-eligible for garbage collection

what does 're-refrences an object' means .

Thanking you in advance

For an object to make itself no long eligible for garbage collection, it needs to have a reference to it from something that is still reachable.

So it needs to have itself (ie. "this") assigned from some reference in some other object that is still reachable.

Henry

[wise owen]

What is resurrection (in garbage collection)?

[Srinivas Kalvala]

Hello,

See this,

 
/**
     * Called by the garbage collector on an object when garbage collection
     * determines that there are no more references to the object.
     * A subclass overrides the <code>finalize</code> method to dispose of
     * system resources or to perform other cleanup. 
     * <p>
     * The general contract of <tt>finalize</tt> is that it is invoked 
     * if and when the Java<font size="-2"><sup>TM</sup></font> virtual 
     * machine has determined that there is no longer any
     * means by which this object can be accessed by any thread that has
     * not yet died, except as a result of an action taken by the
     * finalization of some other object or class which is ready to be
     * finalized. The <tt>finalize</tt> method may take any action, including
     * making this object available again to other threads; the usual purpose
     * of <tt>finalize</tt>, however, is to perform cleanup actions before 
     * the object is irrevocably discarded. For example, the finalize method 
     * for an object that represents an input/output connection might perform
     * explicit I/O transactions to break the connection before the object is
     * permanently discarded. 
     * <p>
     * The <tt>finalize</tt> method of class <tt>Object</tt> performs no 
     * special action; it simply returns normally. Subclasses of 
     * <tt>Object</tt> may override this definition.
     * <p>
     * The Java programming language does not guarantee which thread will 
     * invoke the <tt>finalize</tt> method for any given object. It is 
     * guaranteed, however, that the thread that invokes finalize will not 
     * be holding any user-visible synchronization locks when finalize is 
     * invoked. If an uncaught exception is thrown by the finalize method, 
     * the exception is ignored and finalization of that object terminates.
     * <p>
     * After the <tt>finalize</tt> method has been invoked for an object, no 
     * further action is taken until the Java virtual machine has again 
     * determined that there is no longer any means by which this object can 
     * be accessed by any thread that has not yet died, including possible
     * actions by other objects or classes which are ready to be finalized, 
     * at which point the object may be discarded.
     * <p>
     * The <tt>finalize</tt> method is never invoked more than once by a Java
     * virtual machine for any given object.
     * <p>
     * Any exception thrown by the <code>finalize</code> method causes 
     * the finalization of this object to be halted, but is otherwise 
     * ignored. 
     *
     * @throws Throwable the <code>Exception</code> raised by this method
     */
    
 
        protected void finalize() throws Throwable { }
 

[Barry Gaunt]

The exact same information as the above listing is to be found in class Object's finalize method API documentation. So there is no need to go to the extent of getting the source code in this case - especially because it is more readable in the API.