If a Map had n number of key value pairs and the map becomes unreachable but some of it key value pairs are still reachable then the map will be eligible for garbage collection or not?

If the map will be eligible then what is really collected from the memory, does the internal data structure(internal classes/primitive) which is used by the map class will get garbage collected?

The moment, you garbage collect the Map (either by suggesting JVM by gc command) or routine garbage collection of JVM, all its reference objects in collections become soft links and gets candidate for garbage collection in same or next cyle (most likely for next cycle).