I’ve once made a simple helper class for a set of bytes stored as an integer bitfield. So the idea is that each of the 32bits is used to represent if the ordinal number is in the set or not. This only works for the bytes 0 to 31.
Now this is an “inline class” – something we will get with Project Valhalla.
Here’s the branch of my project:
https://github.com/claudemartin/smallset/tree/valhalla
For this to work you need a JDK with a preview of Project Valhalla. Check java.net for that: http://jdk.java.net/valhalla/
Just download that JDK, clone my branch, build using Ant, and see what you can do with it. It’s actually a good example of an inline class, because it is just an integer (primitive) value but has methods (like a referenced type would). It doesn’t need object identity, but should still behave like an object. For example the sets are comparable. The type actually implements the Comparable interface.
Note that this might not work with newer JDKs. I used JDK 14 + valhalla from java.net and the feature might look quite different in newer releases of Java.