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List:       openjdk-core-libs-dev
Subject:    Re: Inconsistency in Constructor.getGenericParameterTypes()
From:       Oliver Drotbohm <odrotbohm () vmware ! com>
Date:       2021-02-26 22:20:54
Message-ID: AC08AA43-3697-4B8F-92A1-AAEF8947A232 () vmware ! com
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Hi Joe,

thanks for the explanation. We switched to rather iterating over ….getParameters() \
and take it from there. Do you think it makes sense to leave a note about this in the \
Javadoc?

Cheers,
Ollie

> Am 26.02.2021 um 22:38 schrieb Joe Darcy <joe.darcy@oracle.com>:
> 
> Hello Oliver,
> 
> This is long-standing if surprising and under-documented behavior.
> 
> The getGenericFoo methods, when generic type information is present, give a \
> source-level view of the element. At a source level, the implicit outer this \
> parameter is not present and thus omitted by constructor.getGenericParameterTypes \
> for the constructor in question. 
> HTH,
> 
> -Joe
> 
> On 2/26/2021 5:41 AM, Oliver Drotbohm wrote:
> > Previously sent to the wrong list. Sorry for the double post.
> > 
> > Von: Oliver Drotbohm <odrotbohm@vmware.com>
> > Betreff: Inconsistency in Constructor.getGenericParameterTypes()
> > Datum: 25. Februar 2021 um 10:03:12 MEZ
> > An: jdk-dev@openjdk.java.net
> > 
> > Hi all,
> > 
> > we've just ran into the following issue: for a non-static, generic inner class \
> > with a constructor declaring a generic parameter, a call to \
> > constructor.getGenericParameterTypes() does not return the enclosing class \
> > parameter type. Is that by intention? If so, what's the reasoning behind that? 
> > Here's a the output of a reproducer (below):
> > 
> > static class StaticGeneric<T> - names: value, string
> > static class StaticGeneric<T> - parameters: [class java.lang.Object, class \
> > java.lang.String] static class StaticGeneric<T> - generic parameters: [T, class \
> > java.lang.String] 
> > class NonStaticGeneric<T> - names: this$0, value, String
> > class NonStaticGeneric<T> - parameters: [class Sample, class java.lang.Object, \
> > class java.lang.String] class NonStaticGeneric<T> - generic parameters: [T, class \
> > java.lang.String] 
> > class NonStaticNonGeneric - names: this$0, String
> > class NonStaticNonGeneric - parameters: [class Sample, class java.lang.String]
> > class NonStaticNonGeneric - generic parameters: [class Sample, class \
> > java.lang.String] 
> > Note how the constructor of the NonStaticGeneric<T> type exposes three parameter \
> > names, three parameter types but omits the enclosing class parameter in the list \
> > of generic parameter types. 
> > Tested on JDK 8 to 15. Same behavior.
> > 
> > Cheers,
> > Ollie
> > 
> > 
> > class Sample {
> > 
> > 	public static void main(String[] args) {
> > 
> > 		Constructor<?> first = StaticGeneric.class.getDeclaredConstructors()[0];
> > 
> > 		System.out.println("static class StaticGeneric<T> - names: "
> > 				+ Arrays.stream(first.getParameters()).map(Parameter::getName).collect(Collectors.joining(", \
> > ")));  System.out.println("static class StaticGeneric<T> - parameters: " + \
> > Arrays.toString(first.getParameterTypes()));  System.out.println(
> > 				"static class StaticGeneric<T> - generic parameters: " + \
> > Arrays.toString(first.getGenericParameterTypes())); 
> > 		System.out.println();
> > 
> > 		Constructor<?> second = NonStaticGeneric.class.getDeclaredConstructors()[0];
> > 		System.out.println("class NonStaticGeneric<T> - names: "
> > 				+ Arrays.stream(second.getParameters()).map(Parameter::getName).collect(Collectors.joining(", \
> > ")));  System.out.println("class NonStaticGeneric<T> - parameters: " + \
> > Arrays.toString(second.getParameterTypes()));  System.out
> > 				.println(
> > 						"class NonStaticGeneric<T> - generic parameters: " + \
> > Arrays.toString(second.getGenericParameterTypes())); 
> > 		System.out.println();
> > 
> > 		Constructor<?> third = NonStaticNonGeneric.class.getDeclaredConstructors()[0];
> > 		System.out.println("class NonStaticNonGeneric - names: "
> > 				+ Arrays.stream(third.getParameters()).map(Parameter::getName).collect(Collectors.joining(", \
> > ")));  System.out.println("class NonStaticNonGeneric - parameters: " + \
> > Arrays.toString(third.getParameterTypes()));  System.out
> > 				.println(
> > 						"class NonStaticNonGeneric - generic parameters: " + \
> > Arrays.toString(third.getGenericParameterTypes()));  }
> > 
> > 	static class StaticGeneric<T> {
> > 		StaticGeneric(T value, String string) {}
> > 	}
> > 
> > 	class NonStaticGeneric<T> {
> > 		NonStaticGeneric(T value, String String) {}
> > 	}
> > 
> > 	class NonStaticNonGeneric {
> > 		NonStaticNonGeneric(String String) {}
> > 	}
> > }
> > 



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