Hi Nathan: Nathan Beyer 写道: > I'm still waiting to see a real and non-trivial piece of code that does > this. Does anyone have one? > > I don't disagree with the various comments about class design, but this > seems indicative of a larger problem with the entire implementation. > Thank you for your agreement. :-) Can I conclude that you do think this may be a design pitfall and will bring potential problem.
Best regards > -Nathan > > >> -----Original Message----- >> From: Andrew Zhang [mailto:[EMAIL PROTECTED] >> Sent: Wednesday, September 20, 2006 3:28 AM >> To: harmony-dev@incubator.apache.org >> Subject: Re: [classlib][luni] JIRA 1492 Constructor of HashMap throw >> unexpected exception >> >> Josh Bloch has given an excellent comment on this issue in his famouse >> book "effective java", item 15 "Design and document for inheritance or >> else >> prohibit it". >> [quote from "effective java"] >> There are a few more restrictions that a class must obey to allow >> inheritance. Constructors >> must not invoke overridable methods, directly or indirectly. If this rule >> is >> violated, it is >> likely that program failure will result. The superclass constructor runs >> before the subclass >> constructor, so the overriding method in the subclass will get invoked >> before the subclass >> constructor has run. If the overriding method depends on any >> initialization >> performed by the >> subclass constructor, then the method will not behave as expected. >> [/quote] >> >> So I'd like to agree with Paulex that we'd better fix this problem. :-) >> >> >> On 9/20/06, Alexey Petrenko <[EMAIL PROTECTED]> wrote: >> >>> Are you trying to say that the methods in Harmony can use only methods >>> used in corresponding RI implementations? >>> >>> 2006/9/20, Spark Shen <[EMAIL PROTECTED]>: >>> >>>> Spark Shen 写道: >>>> >>>>> Hi : >>>>> Following is the discussion about JIRA 1492, shall we discuss it >>>>> >> here? >> >>>>> public class SubMapTest extends TestCase { >>>>> public void testSubclass() { >>>>> HashMap map = new HashMap(); >>>>> map.put("a", "a"); >>>>> SubMap map2 = new SubMap(map); // Harmony will throw an unexpected >>>>> exception here. >>>>> } >>>>> } >>>>> >>>>> class SubMap<K, V> extends HashMap<K, V> { >>>>> >>>>> public V put(K key, V value) { >>>>> throw new RuntimeException(); >>>>> } >>>>> } >>>>> >>>>> >>>>> >>>>>> Nathan Beyer >>>>>> Harmony's behavior may be different in this case, but I'm not sure >>>>>> >> I >> >>>>> would consider this a valid issue. What's a real use case for this >>>>> type of sub-classing? >>>>> [ Show ≫ <http://issues.apache.org/jira/browse/HARMONY-1492> ] >>>>> Nathan Beyer >>>>> <http://issues.apache.org/jira/secure/ViewProfile.jspa?name=nbeyer> >>>>> [18/Sep/06 08:41 PM] Harmony's behavior may be different in this >>>>> >> case, >> >>>>> but I'm not sure I would consider this a valid issue. What's a real >>>>> use case for this type of sub-classing? >>>>> >>>>> >>>>> >> <http://issues.apache.org/jira/secure/ViewProfile.jspa?name=spark+shen >> >>>>> Spark >>>>> Shen >>>>> >>>>>> What if change the RuntimeException to >>>>>> >> UnsupportedOperationException? >> >>>>> [ Show ≫ <http://issues.apache.org/jira/browse/HARMONY-1492> ] >>>>> spark shen >>>>> >>>>> >> <http://issues.apache.org/jira/secure/ViewProfile.jspa?name=spark+shen >> >>>>> [18/Sep/06 08:48 PM] What if change the RuntimeException to >>>>> UnsupportedOperationException? >>>>> >>>>> >>>>>> Alexey Petrenko >>>>>> I'm not sure that this is a valid issue to. >>>>>> As far as I understood the issue is that Harmony calls put method >>>>>> >> in >> >>>>> constructor while RI does not. Right? >>>>> >>>>> >>>>>> If so I do not see any issue here. >>>>>> >>>> I can not figure out what RI does. And please refer to JIRA 839, it >>>> reports similar use case. >>>> My point here is >>>> 1. we may not be able to predict how users will use our library. >>>> 2. Users could guess our implementation w/o difficulty, which >>>> contradicts the encapulation priciple. >>>> So I prefer to follow RI on this behavior. >>>> >>>> When changing to UnsupportedOperationException, the use case is more >>>> practical, since it is highly like that put operation is not >>>> >> supported. >> >>>> But it seems not so practical that this sub-hashMap can not be >>>> instantiated. May be one more assertion can convince you that this is >>>> >>> bug. >>> >>>> public class SubMapTest extends TestCase { >>>> public void testSubclass() { >>>> HashMap map = new HashMap(); >>>> map.put("a", "a"); >>>> SubMap map2 = new SubMap(map); >>>> assertEquals(1, map2.size()); >>>> } >>>> } >>>> >>>> class SubMap<K, V> extends HashMap<K, V> { >>>> public SubMap(Map<? extends K, ? extends V> m) { >>>> super(m); >>>> } >>>> >>>> public V put(K key, V value) { >>>> throw new RuntimeException(); >>>> } >>>> } >>>> >>>> Best regards >>>> >>>> -- >>>> Spark Shen >>>> China Software Development Lab, IBM >>>> >>>> >>>> --------------------------------------------------------------------- >>>> Terms of use : http://incubator.apache.org/harmony/mailing.html >>>> To unsubscribe, e-mail: [EMAIL PROTECTED] >>>> For additional commands, e-mail: [EMAIL PROTECTED] >>>> >>>> >>>> >>> -- >>> Alexey A. Petrenko >>> Intel Middleware Products Division >>> >>> >> >> -- >> Andrew Zhang >> China Software Development Lab, IBM >> > > > --------------------------------------------------------------------- > Terms of use : http://incubator.apache.org/harmony/mailing.html > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > > -- Spark Shen China Software Development Lab, IBM --------------------------------------------------------------------- Terms of use : http://incubator.apache.org/harmony/mailing.html To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
