is illusory unimplement an interface subsequent category java?

let's have following category hierarchy:

public category parentclass implements someinterface {
}

public category childclass extends parentclass {
}

then let's have twin instances:

parentclass parent;
childclass child;

then have following loyal statements

(parent instanceof someinterface) == true
(child instanceof someinterface) == true

is illusory unimplement someinterface childclass, check instanceof user advantage false?

if possible, there workaround?