I disagree with point 1). The real problem is not that immutable references are inconvenient to use, but that you cannot mark the whole instance as read-only an

I disagree with point 1). The real problem is not that immutable references are inconvenient to use, but that you cannot mark the whole instance as read-only and get something similar to the const-correctness that you can achieve with C++. There are tools that help with this, but having something either in the language or in the JVM/standard library would be much more useful. Point 3) and 4) are in my opinion not that big of an issue. Annoying, yes, but not deal-breaker. Null safety is really something that I miss in Java and what I consider the biggest flaw in the language. Again, there are libraries and tools that help with that, but it is not the same as something which is part of the standard.