I don’t expose it at the boundaries, just within functions. With everything outside of the function I take a Map interface in and/or return the Map out.
replyIt makes no difference to the outside code.
You are communicating with future readers of the code. The presence of ConcurrentHashMap will lead future engineers into believing the code is threadsafe. This isn't true, and believing it is dangerous.
replyNo, they'll believe that that specific map is thread safe.
replyThat's really not much better. No function is an island, as wise man almost once said.
replyIt’s actually a lot better. That’s literally the whole point of interfaces and polymorphism: to make it so the outside does not care about the implementation.
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