Compiling
import java.util.concurrent.Callable;
class Ideone
{
Callable<?> x = super::clone;
}
using Oracle JDK gives:
Main.java:6: error: incompatible types: invalid method reference
Callable<?> x = super::clone;
^
clone() has protected access in Object
which makes no sense as a class should be able to access its parent's protected methods. This expression works fine in Eclipse's compiler.
Also, () -> super.clone()
compiles fine....
Is this a bug?
super
is not actually an expression, and there's no static type to talk about. super.foo()
has the same access as this.foo()
; it's just that, the method invocation is translated differently in byte code, as "super invoke", as opposed to "normal invoke".
JLS is not very clear on this; e.g. in section of protected access, the super.protectedMember
form is not mentioned; but obviously that form should be discussed in JLS; and it should be accessible. (The section does suggest that X::m
and X.m
should be treated the same w.r.t. access right)
In the section of method reference, the wording is also vague; nevertheless, super::clone
should be accessible the same ways as super.clone()
is accessible.
A bug report has been created: JDK-8139836: “Can't use super::x method reference when x is protected”. Its current status is that it will be fixed in Java 9.
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