w3hJava

Finalization is mostly used in Java to reclaim resources, native resources. Say, you are writing one program using Windows Font(OS font). So, its the programmers duty to reclaim the font resource associated with any object.

If you are an application developer and uses lot of native resource then I would say stop reading this blog and read the latest Article(yes,Sep 2007) by Tony Printezis on sun site. This article is awesome and covers all the cases and its solution that can happen with Memory Retention. The simplest of that is what I am going to talk here.

class PlayWithFont {
String someText;
String newText;
private native method getFont();
void get() {
getFont();
}
// always be called by any method of this class only
private native method releaseFont();
void release() {
releaseFont();
}
protected void finalize() {
release();
}
}

Now, here I have some text and I am taking OS font, converting that text into some fancy text and then releasing the resource of Operating Systems. We have a class called PlayMoreWithFont which basically
inherits PlayWithFont and converting some String[] text into new String[] text (just a fictitious example)

class PlayMoreWithFont {
String[] someMoreText ; // lets consider it here some big chucks of memory
String[] newMoreText;
}

PlayMoreWithFont don’t have any finalize method defined, but off course its going to take one from PlayWithFont.

GC maintain a finalization queue. When a object is unreachable, object is added to the finalization queue. After that only, object goes into finalized state. Now when we called :

play = new PlayMoreWithFont;
play = null;

Now instance of PlayMoreWithFont become unreachable, but reclamation of big chunks like someMoreText and newMoreText has to wait until the instance is finalized. And this is one of the major causes of memory retention.
Moreover the problem is difficult to find if the class hierarchy is big and finalize is sitting some where very deep. There are some good solution which we can discuss in next.

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