Hello Stefan,
2015-01-30 20:41 GMT+01:00 Stefan Bodewig <bode...@apache.org>:
> On 2015-01-30, Gary Gregory wrote:
>
> > On Fri, Jan 30, 2015 at 6:06 AM, Stefan Bodewig <bode...@apache.org>
> wrote:
>
> >> The superclass of ZCompressorInputStream has changed from one we've
> >> removed with the old __internal__ package to a new one in the now
> >> supported lzw package.
>
> > Well, we cannot break BC in a minor release for a public class. Are
> > we sure BC breaks?
>
> Well, not as much as my intuition had told me:
>
> public static void main(String[] args) throws Exception {
> try (InputStream in = new FileInputStream(args[0]);
> OutputStream out = new FileOutputStream(args[1]);
> ZCompressorInputStream zin = new ZCompressorInputStream(in) {
> @Override
> public void close() throws IOException {
> System.err.println("closing with code size " +
> codeSize);
> setClearCode(12);
> super.close();
> }
> }) {
> IOUtils.copy(zin, out);
> }
> }
>
> accesses a protected field and a protected method of
> InternalLZWInputStream when compiled against 1.9, a class that is no
> longer there in 1.10. When run against trunk (without recompiling) it
> still works. This is in line with something I once read up in the JLS
> (oh my, nine years ago, time flies)[1]. The compiler says "call the
> protected setClearCode method taking an int arg" and at runtime it
> starts searching for that method with the most derived class. So
> changing superclasses doesn't seem to affect things.
>
> Of course we will break someting like
>
> InternalLZWInputStream s = new ZCompressorInputStream(in)
>
> but then again you'd have used a class that we had explicitly marked as
> internal.
>
> Unless anybody comes up with a case where the change in superclass
> causes a problem, I'd say we are fine.
>
thank you for the research!
What will happen if a client has overwritten a method from
InternalLZWInputStream?
public static void main(String[] args) throws Exception {
try (InputStream in = new FileInputStream(args[0]);
OutputStream out = new FileOutputStream(args[1]);
ZCompressorInputStream zin = new ZCompressorInputStream(in) {
@Override
public void setClearCode(int code) throws IOException {
// reinvent the wheel here...
}
}) {
IOUtils.copy(zin, out);
}
}
My gut feeling tells me this will work as well, but we better double check
to avoid jar hell :-)
Benedikt
>
> Stefan
>
> [1]
> http://stefan.samaflost.de/blog/en/dotNet/difference_between_java_and_csharp.html
>
>
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