java - Why does LongProperty implement Property<Number> but not Property<Long>? -

i have come across seems peculiarity in javafx api: longproperty implements property<number>, not property<long>.

what reason this? sort of idea stems java's inherent problem covariance , contravariance, because generics implemented stupidly via erasure, maintain backwards compatibility bytecode; problem have arisen having longproperty implement both property<number> and property<long>?

edit: question originated problem: apply longproperty tablecolumn programmatically (vs semantically)

it can't implement both.

to that, need implement 2 versions of each method in interface uses generic. let's take 1 example:

bindbidirectional(property<long> other) { ... } 

under hood, erasure means gets compiled down to:

bindbidirectional(property other) { ... } 

so then, implements property<number> , property<long> do? have 2 methods:

bindbidirectional(property<long> other) { ... } bindbidirectional(property<number> other) { ... } 

... compile down, after erasure, 2 methods:

bindbidirectional(property other) { ... } bindbidirectional(property other) { ... } 

these 2 methods conflict, , there'd no way resolve them @ runtime.

even if used compiler trickery around this, happens when uses longproperty raw property?

property rawlongproperty = new longproperty(); rawlongproperty.bindbidirectional(someotherrawproperty); 

there's no way know of 2 binddirectional variants meant resolve to.