because compiler can at compile-time tell, that t (Ticker) is not related to String. Compiler knows that Ticker is not ancestor nor descendant of String, and consider parameters (of instanceof) as incompatible.
try to change t to Object variable
and now it is working. t is of type Object, so it is possible to have String object reference in type Object reference (upcasting).
when t is Ticker, it doesn't look like upcasting, doesn't look like downcasting, and you have compile-time error: incompatible types
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