Question

Through google, there are found many slightly different solutions to this, even though (to me) it feels like it should be much easier to answer. These are the words I’m worrying about right now, while trying to acquire decent UML’ing skills :D…

“public, protected, private, package”

Let me first try to get this complete for Java, because I feel pretty familiar with it (correct me please, if I did any evil nevertheless!):

1. Public
   • Members of the same instance can see/use this
   • Members of another instance of the same class can see/use this
   • Members of derivative classes in the same pkg can see/use this
   • Members of derivative classes in another pkg can see/use this
   • Members of another class in the same pkg can see/use this
   • Members of another class in another pkg can see/use this
   • Anything else can see/use this
2. Protected
   • Members of the same instance can see/use this
   • Members of another instance of the same class can see/use this
   • Members of derivative classes in the same pkg can see/use this
   • Members of derivative classes in another pkg can see/use this
   • Members of another class in the same pkg cannot see/use this
   • Members of another class in another pkg cannot see/use this
   • Anything else cannot see/use this
3. Private
   • Members of the same instance can see/use this
   • Members of another instance of the same class can see/use this
   • Members of derivative classes in the same pkg cannot see/use this
   • Members of derivative classes in another pkg cannot see/use this
   • Members of another class in the same pkg cannot see/use this
   • Members of another class in another pkg cannot see/use this
   • Anything else cannot see/use this
4. Package
   • Members of the same instance can see/use this
   • Members of another instance of the same class can see/use this
   • Members of derivative classes in the same pkg can see/use this
   • Members of derivative classes in another pkg cannot see/use this
   • Members of another class in the same pkg can see/use this
   • Members of another class in another pkg cannot see/use this
   • Anything else cannot see/use this

My questions now:

1. How exactly does this differ from the UML standard?
2. Where did I include errors in the upper list, if I did? I’m not god, so there might be one 😉

Best regards, and thanks in advance for any help!

Answer 1

From the UML standard. Visibility:

A public element is visible to all elements that can access the contents of the namespace that owns it.

A private element is only visible inside the namespace that owns it.

A protected element is visible to elements that have a generalization relationship to the namespace that owns it.

A package element is owned by a namespace that is not a package, and is visible to elements that are in the same package as its owning namespace. Only named elements that are not owned by packages can be marked as having package visibility. Any element marked as having package visibility is visible to all elements within the nearest enclosing package (given that other owning elements have proper visibility). Outside the nearest enclosing package, an element marked as having package visibility is not visible.

Namespace:

A namespace is a named element that can own other named elements.

I think the UML definitions of private, protected, etc. are fairly similar to those of Java.