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 <odrotb...@vmware.com>
Betreff: Inconsistency in Constructor.getGenericParameterTypes()
Datum: 25. Februar 2021 um 10:03:12 MEZ
An: jdk-...@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) {}
}
}
