finalize : Java Glossary

finalize

Note the z American spelling is finalize. Java has all sorts of mechanisms for running special initialisation code, but it is rather weak on dealing with finalisation code. You can add a method called finalize to any class.

protected void finalize() throws Throwable {...}

When a object is about to be garbage collected, its finalize method will be run. The catch is, at shutdown, by default the finalizers are not run on all unreachable objects, so you can’t count on them to do things like close files.

// Force finalize methods to be run on exit
// Without this, unreachable objects may not
// have had finalize run when you quit.
System.runFinalizersOnExit( true );

Under no circumstances are finalizers run on reachable objects, so you can’t use them to close files for example.

You can also register a hunk of code to be run like this:

Runtime.addShutdownHook( Thread hook );

Unfortunately, addShutdownHook takes a memory-hogging Thread rather than a lightweight Runnable.

Some feel finalize should be deprecated, and you should use phantom references instead since they give much better performance. Finalizers interfere with garbage collection. Their main use is debugging. Use them to issue an error message is an object is garbage collected without its close(), dispose(), disconnect()… method being called.

dispose
final
finally
phantom references
shutdown

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