Due to processing use of inner class, private modifier does not actually enforces privacy at all; is there any reason why private is legal? Why not make private modifier causes compilation error instead of making false promise.



As an aside, is there any way to make this class immutable:

class Line {
 private final PVector start;
 private final PVector end;
 // etc...
}

If private had actually worked, we can ensure PVector cannot be modified by instantiating PVector inside Line's constructor and the private modifier guarantee that noone outside our class have access to the actual PVector object. But since private doesn't really do anything, that guarantee does not hold. I can use final .x1, .x2, .x3, .y1, .y2, .y3 instead of PVector; but that means I can't use PVector operations (.cross, .dot, .add, .sub, .mult, etc); not easily at least.

No, I don't. As you see, my personal favorite language of choice is python, for which there is no such thing as access control so I am not really concerned about the lack of privacy itself¹.

What I do gets me a bit nervous, is the fact that `private` is legal but does not actually do anything. Even if it's provided for source-level compatibility with existing Java code, shouldn't there be a warning that it does not do what you expect it to do?

¹ although a working "private final" modifier would be nice since it guarantees immutability, so I don't even need to think about possibility of accidentally mutating somewhere; however I don't actually mind being courteous and not accessing private data myself (as I would have done in python). The lack of actual privacy is the least of my concern.

private is not working in Processing (at least in .pde files, it works in .java files...) because all classes are inner classes, so have access to the internals of their siblings/parents. There was recently a similar thread on the topic.

Somehow, if you really want it, you can still use the private as it still has a documentation value: it means "don't touch this variable directly". The developer (yourself, in general, in most Processing projects) can still do direct access, but that's at his/her own risk...