Re: Throwing Constructor Exceptions and cleaning up

From:
Lew <lew@lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Fri, 3 Apr 2009 13:47:06 -0700 (PDT)
Message-ID:
<60b4d7bf-73f4-472b-98b2-2761472927a1@p11g2000yqe.googlegroups.com>
Peter Duniho wrote:

As you say, the finalizer is not part of normal operation. It's there =

as

a fail-safe. So, for classes that do need that fail-safe in order to =

 

ensure that buggy client code doesn't break things, it's useful as a
performance optimization for the run-time to provide a way for the class =

 

to inform the run-time that the fail-safe behavior isn't needed, because =

 

the requisite cleanup has already been done.


There is such a way - do not override 'finalize()'. That informs the
runtime "that the fail-safe behavior isn't needed".

It occurs to me that Java could in fact include this.


It already does.

If the run-time tracks whether the finalize() method has been called, as =

opposed to

tracking whether the _run-time_ calls the finalize() method (I realize th=

e

difference is subtle, but it's there), then if the class uses an explicit=

  

call to finalize() in order to perform its own cleanup, or even simply as=

  

In Java, the class should not call 'finalize()' - that's not the
purpose. The purpose of 'finalize()' is to work with GC in certain
rare scenarios. It is not as general-purpose as the .NET finalizer.
The way the class does its own cleanup is to call some method that
does not override 'finalize()'.

a signal to the run-time that it's been cleaned up, then that would allow=

  

the run-time to know the cleanup has been done and not put the object int=

o

the list of objects needing finalization.


Again, Java has that feature as the default behavior. Unless you
override 'finalize()', the runtime does not put it in the list of
objects needing finalization.

Whether Java does in fact do that, I don't know. But it could.


In effect, it does, but it does it the other way around from your
description. In Java, the default behavior is not to put the object
into the finalization queue. You signal to the runtime that the
class's objects do need to be finalized by overriding the 'finalize()'
method (nontrivially).

In Java, the best practice is to call some method that doesn't
override 'finalize()' to do cleanup, then remove all references to it
as a signal to GC to clean it up. Only in the very rare use cases
where you need to tie some action to GC-time cleanup do you override
'finalize()' nontrivially.

--
Lew

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