Java Reference
In-Depth Information
}
}
Note that
close
is carefully written to be correct if it is invoked more than
once. Otherwise, if someone invoked
close
, finalizing the object would
cause another close on the file, which might not be allowed.
Note also that, in this example,
finalize
invokes
super.finalize
in a
fi-
nally
clause. Train yourself so that you always write that invocation in
any
finalize
method you write. If you don't invoke
super.finalize
, you
may correctly finalize your own part of the object, but the superclass's
part will not get finalized. Invoking
super.finalize
is one of those good
habits you should adopt even when your class doesn't extend any other
class. In addition to being good training, invoking
super.finalize
in such
a case means that you can always add a superclass to a class like
Pro-
cessFile
without remembering to examine its
finalize
method for cor-
rectness. Invoking the superclass's
finalize
method in a
finally
clause
ensures that the superclass's cleanup will happen even if your cleanup
causes an exception.
The garbage collector may reclaim objects in any order or it may never
reclaim them. Memory resources are reclaimed when the garbage col-
lector thinks the time is appropriate. Not being bound to an ordering
guarantee, the garbage collector can operate in whatever manner is
most efficient, and that helps minimize the overhead of garbage collec-
tion. You can, if necessary, invoke the garbage collector to try to force
earlier collection using
System.gc
or
Runtime.gc
, as you'll see in the next
section, but there is no guarantee that garbage collection will actually
occur.
When an application exits, no further garbage collection is performed,
so any objects that have not yet been collected will not have their
fi-
nalize
methods invoked. In many cases this will not be a problem. For
example, on most systems when the virtual machine exits, the under-
lying system automatically closes all open files and sockets. However,
for non-system resources you will have to invent other solutions. (Tem-
