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^{If you're interested, a more detailed analysis of Puzzle 90 is provided in this answer at Stack Overflow.}

^{If you're interested, a more detailed analysis of Puzzle 90 is provided in this answer at Stack Overflow.}

Overall, my (quite painful) encounters with debugging inner classes directly accessing fields of enclosing instance made strong impression that this practice resembles use of global state, along with known evils associated with it.

For the sake of completeness, there may be cases where above reasoning doesn't apply. For example, per my reading of map.keySet javadocs, this feature suggests tight coupling and as a result, invalidates arguments against non-static classes:

Overall, my (quite painful) encounters with debugging inner classes directly accessing fields of enclosing instance made strong impression that this practice resembles use of global state, along with known evils associated with it.

For the sake of completeness, there may be cases where above reasoning doesn't apply. For example, per my reading of map.keySet javadocs, this feature suggests tight coupling and as a result, invalidates arguments against non-static classes:

For the sake of completeness, there may be cases where above reasoning doesn't apply. For example, per my reading of map.keySet javadocs, this feature suggests tight coupling and as a result, invalidates arguments against non-static classes:

Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa...

Not that above would somehow make involved code easier to maintain, test and debug mind you, but it at least could allow one to argue that complication matches / is justified by intended functionality.