java - How can I make extensions of interfaces compatible with generic parameters? -

follow this question, i'll try make self-contained.

suppose have interface called animal, various reasons has generic type parameter representing implementing class:

public interface animal<a extends animal<a>> 

i have sub-interface, dinosaur, behaves in same way:

public interface dinosaur<d extends dinosaur<d>> extends animal<d> 

now have class lizard implements animal:

public class lizard implements animal<lizard> 

and subclass, trex, implements dinosaur:

public class trex extends lizard implements dinosaur<trex> 

these 4 declarations produce error. because class trex implements interface animal twice, different type parameters: since extends lizard, implements interface animal<lizard>, , since implements dinosaur<trex>, implements animal<trex>.

animal<trex> not subinterface of animal<lizard>, though trex subclass of lizard, compiler error.

i'm sure there's way around using wildcards, can't work out is.

here's can compile same error:

public class interfacetest {   private interface animal<a extends animal<a>> {}    private interface dinosaur<d extends dinosaur<d>> extends animal<d> {}    private class lizard implements animal<lizard> {}    private class trex extends lizard implements dinosaur<trex> {} } 

this because class trex implements interface animal twice, different type parameters

yup, case, , there's no way around directly - it's technical limitation because generics implemented using erasure. you can never implement same interface on more 1 class different generic parameters. when generic types erased you'd end extending 2 interfaces identically, no way distinguish between methods making use of different generic types, , no way runtime determine method execute.

for particular use case there's workaround means don't have implement same interface different type parameters, without more details it's impossible might be.

edit: looking @ linked question, looks solve problem using other answer (the 1 haven't accepted) specifies return value in way rather declaring on class:

public <t extends jnumber> t add(t addend); 

this should mean don't need declare generic type parameter on classes , interfaces, , shouldn't have issue.