Question

Possible Duplicate:
Why is there no sub-class visibility modifier in Java?

The access level table for Java, shows 4 different options for controlling access to members of a class:

Modifier    Class  Package Subclass World
public      Y      Y       Y        Y
protected   Y      Y       Y        N
no modifier Y      Y       N        N
private     Y      N       N        N

There is no modifier, however, for “accessible to class and subclass only”. That is:

Modifier    Class  Package Subclass World
c++prot     Y      N       Y        N

Is it possible at all to define such access level in Java?

If so, how?

If this isn’t possible, this must be due to a well thought design principle. If so, what is that principle. In other words, why having such access level in Java isn’t a good idea?

Answer 1

The design principle is that developers do not maliciously hack their own programs. If you don’t trust classes in the same package to behave correctly you have serious non-technical issues IMHO.

The access modifiers are there to restrict accidental errors, and they attempt to stop most error with minimum complexity.

BTW: with reflection/JNI calls you can bypass all access modifiers, so they are not a rock solid security measure IMHO.