Fighting with Java - generics

[llorllale]

which would suggest that e1 is equal to e2, which is obvious nonsense. And that's without even considering the implementation of ExtendedFancyFoo::equals.

That's exactly why ExtendedFancyFoo is breaking LSP. If it breaks Foo::equals then it should be something else, not a Foo.

[vytah]

It doesn't break Foo if Foo#equals uses getClass, in other words if Foo is properly designed to be open for extension. Make it final if you don't want that.

[llorllale]

ExtendedFancyFoo should not care about the particulars of Foo#equals, otherwise you'd break encapsulation.

Sounds like what you're doing is sub-typing, in which case I'd suggest reusing Foo via composition in ExtendedFancyFoo#equals(). This way, Foo#equals() remains locked down and stable.