Inconsistency in Constructor.getGenericParameterTypes()
Oliver Drotbohm
odrotbohm at vmware.com
Fri Feb 26 13:41:48 UTC 2021
Previously sent to the wrong list. Sorry for the double post.
Von: Oliver Drotbohm <odrotbohm at vmware.com>
Betreff: Inconsistency in Constructor.getGenericParameterTypes()
Datum: 25. Februar 2021 um 10:03:12 MEZ
An: jdk-dev at 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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