Comment by bluetech

Java actually doesn't need to add any features for it to support this, it needs to remove them. I recommend reading this excellect article: http://habitatchronicles.com/2017/05/what-are-capabilities/

The gist is:

Rule #1: All instance variables must be private

Rule #2: No mutable static state or statically accessible authority

Rule #3: No mutable state accessible across thread boundaries