RFR: 8062389,8029459,8061950: Class.getMethod() is inconsistent with Class.getMethods() results + more

Daniel Fuchs daniel.fuchs at oracle.com
Tue Oct 11 15:19:43 UTC 2016

Hi Peter,

I was looking at the test - I didn't see a case where the
same method would be declared by two unrelated interfaces
later implemented by the same class.
Do we have test cases to verify that:

public interface I1 {
     public Object test(String blah);
public interface I2 {
     public Object test(String blah);
public abstract class A implements I2 {}
public abstract class A1 extends A implements I1, I2 {}
public abstract class A2 implements I1, I2 {}
public abstract class A3 implements I2, I1 {}

A1.getMethods(), A2.getMethods(), A3.getMethods() return
the expected result?
In particular what should A2.class.getMethods()
and A3.class.getMethods() return?

best regards,

-- daniel

On 10/10/16 09:04, Peter Levart wrote:
> Just a note that this is still ready to be reviewed.
> I was also told that JCK tests pass with the patch applied.
> Regards, Peter
> On 10/04/2016 03:40 PM, Peter Levart wrote:
>> Hi,
>> I have a fix for conformance (P2) bug (8062389
>> <https://bugs.openjdk.java.net/browse/JDK-8062389>) that also fixes a
>> conformance (P3) bug (8029459
>> <https://bugs.openjdk.java.net/browse/JDK-8029459>) and a performance
>> issue (8061950 <https://bugs.openjdk.java.net/browse/JDK-8061950>):
>> http://cr.openjdk.java.net/~plevart/jdk9-dev/Class.getMethods.new/webrev.04/
>> As Daniel Smith writes in 8029459
>> <https://bugs.openjdk.java.net/browse/JDK-8029459>, the following
>> situation is as expected:
>> interface I { void m(); }
>> interface J extends I { void m(); }
>> interface K extends J {}
>> K.class.getMethods() = [ J.m ]
>> But the following has a different result although it should probably
>> have the same:
>> interface I { void m(); }
>> interface J extends I { void m(); }
>> interface K extends I, J {}
>> K.class.getMethods() = [ I.m, J.m ]
>> He then suggests the following algorithm:
>> An implementation of getMethods consistent with JLS 8 would include
>> the following (see Lambda Spec, Part H, 9.4.1 and 8.4.8):
>> 1) The class's/interface's declared (public) methods
>> 2) The getMethods() of the superclass (if this is a class), minus any
>> that have a match in (1)
>> 3) The getMethods() of each superinterface, minus any that have a
>> match in (1) or a _concrete_ match in (2) or a match from a
>> more-specific class/interface in (2) or (3)
>> But even that is not sufficient for the following situation:
>> interface E { void m(); }
>> interface F extends E { void m(); }
>> abstract class G implements E {}
>> abstract class H extends G implements F {}
>> H.class.getMethods() = [ E.m, F.m ]
>> The desired result of H.class.getMethods() = [ F.m ]
>> So a more precise definition is required which is implemented in the fix.
>> The getMethods() implementation partitions the union of the following
>> methods:
>> 1) The class's/interface's declared public methods
>> 2) The getMethods() of the superclass (if this is a class)
>> 3) The non-static getMethods() of each direct superinterface
>> ...into equivalence classes (sets) of methods with same signature
>> (return type, name, parameter types). Within each such set, only the
>> "most specific" methods are kept and others are discarded. The union
>> of the kept methods is the result.
>> The "more specific" is defined as a partial order within a set of
>> methods of same signature:
>> Method A is more specific than method B if:
>> - A is declared by a class and B is declared by an interface; or
>> - A is declared by the same type as or a subtype of B's declaring type
>> and both are either declared by classes or both by interfaces (clearly
>> if A and B are declared by the same type and have the same signature,
>> they are the same method)
>> If A and B are distinct elements from the set of methods with same
>> signature, then either:
>> - A is more specific than B; or
>> - B is more specific than A; or
>> - A and B are incomparable
>> A sub-set of "most specific" methods are the methods from the set
>> where for each such method M, there is no method N != M such that N is
>> "more specific" than M.
>> There can be more than one "most specific" method for a particular
>> signature as they can be inherited from multiple unrelated interfaces,
>> but:
>> - javac prevents compilation when among multiply inherited methods
>> with same signature there is at least one default method, so in
>> practice, getMethods() will only return multiple methods with same
>> signature if they are abstract interface methods. With one exception:
>> bridge methods that are created by javac for co-variant overrides are
>> default methods in interfaces. For example:
>>     interface I { Object m(); }
>>     interface J1 extends I { Map m(); }
>>     interface J2 extends I { HashMap m(); }
>>     interface K extends J1, J2 {}
>> K.class.getMethods() = [ default Object j1.m, abstract Map j1.m,
>> default Object j2.m, abstract HashMap j2.m ]
>> But this is an extreme case where one can still expect multiple
>> non-abstract methods with same signature, but different declaring
>> type, returned from getMethods().
>> In order to also fix 8062389
>> <https://bugs.openjdk.java.net/browse/JDK-8062389>, getMethod() and
>> getMethods() share the same consolidation logic that results in a set
>> of "most specific" methods. The partitioning in getMethods() is
>> partially performed by collecting Methods into a HashMap where the
>> keys are (name, parameter types) tuples and values are linked lists of
>> Method objects with possibly varying return and declaring types. The
>> consolidation, i.e. keeping only the set of most specific methods as
>> new methods are encountered, is performed only among methods in the
>> list that share same return type and also removes duplicates.
>> getMethod() uses only one such list, consolidates methods that match
>> given name and parameter types and returns the 1st method from the
>> resulting list that has the most specific return type.
>> That's it for algorithms used. As partitioning partially happens using
>> HashMap with (name, parameter types) keys, lists of methods that form
>> values are typically kept short with most of them containing only a
>> single method, so this fix also fixes performance issue 8061950
>> <https://bugs.openjdk.java.net/browse/JDK-8061950>.
>> The patch also contains some optimizations around redundant copying of
>> arrays and reflective objects.
>> The FilterNotMostSpecific jtreg test has been updated to accommodate
>> for changed behavior. Both of the above extreme cases have been added
>> to the test.
>> So, comments, please.
>> Regards, Peter

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