[kykat]

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.

[gf000]

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.