I think it's more of a legal/licensing move than a technical challenge. You write and compile Java but then it's translated to bytecode for a different VM (Dal

I think it's more of a legal/licensing move than a technical challenge. You write and compile Java but then it's translated to bytecode for a different VM (Dalvik, I presume this is still the case though I hear there's additional native compilation that occurs now). Net result, developers get to write Java but Google doesn't have to pay royalties for a proper VM on every device.