V8 automatically optimizes objects with the same shape into efficient structs, making array of objects much more efficient than in Java.
And the manually manager int array acts more like system memory, it's not continuous, so you could have point i 0 and 2 and the data would be:
[1, 2, 3, x, x,x, 3, 2, 1] (3D points).
The optimization you discussed for GIS data is called struct of arrays. JavaScript does not do that automatically for you. You would have to do the same thing manually in JavaScript to avoid per-triple object overhead.
Hidden class optimizations just make JavaScript objects behave a little more like Java class instances, where the VM knows where to find each field, rather than having to look it up like a map.
It doesn't make JS faster than Java, it makes it almost as fast in some cases.
I can only say what I observed in testing, and that's that having millions of instances of a class like Point3D{x, y, z} in JS uses significantly less memory than in Java (this was tested on Android, not sure if relevant). It was quite some time ago so I don't remember the details.
Well, Android is not running Java, it runs Android runtime (dalvik) byte code. In general, depending on when it was, that runtime is much much simpler and does a lot more at compile time at the expense of less JIT optimization.
It's also many versions behind the Java API (depending on when it happened).
So your data point is basically completely irrelevant.
