Question

Poking around Android API sources. There’s FileDescriptor with a data member descriptor with no access modifier:

int descriptor;

Then there’s class FileOutputStream that constructs a new FileDescriptor and assigns to that field:

fd = new FileDescriptor();
fd.descriptor = fileSystem.open(...);

How is that compatible with the field access control model of Java? I thought package-private fields are not accessible from outside the declaring class, and there’s no notion of friendship like in C++.

Answer 1

Basically, package-private can be accessed at the class and package levels:

From the source:

Access Levels
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