This article has a bit of a false dichotomy for why reified generics we’re not possible. It says roughly: 1. We must make the existing ArrayList become a gener

This article has a bit of a false dichotomy for why reified generics we’re not possible. It says roughly: 1. We must make the existing ArrayList become a generic type. 2. If Java’s generic system was reified, that would be a backwards incompatible change. 3. Therefore reified generics are not possible to implement in a backwards compatible way. Ok, sure, but if you instead a new generic collection types and leave the old ones alone, you don’t have to worry about breaking existing compiled code. This comment about C# suggests a lack of familiarity with the approach C# took: > C# made the opposite choice — to update their VM, and invalidate their existing libraries and all the user code that dependend on it. All of the pre-generic C# libraries continue to exist to this day (ArrayList, HashTable, and the non-generic IEnumerable). Applications that used them never stopped working. New code uses the generic collections (List<T> and Dictionary<TKey, TValue>). Anyways, I think the costs that Java is currently paying for non-reified generics (reflection, performance, and type safety mentioned in the article) is not worth the backwards comparability with the 20 year old J2SE 1.4. The price C# pays for making a backwards incompatible generics (mostly some minor annoyance when designing a collection class implementing IEnumerable) is worth it at this point. P.S. ok, I do admit that C# forking the collection library is still causing ongoing maintenance work 18 years later: https://github.com/dotnet/winforms/pull/8673 https://github.com/dotnet/winforms/pull/8673