The Java Language Specification, Third Edition

8.2.1 Examples of Inheritance CLASSES
194
class Point3d extends Point {
int z;
void move(int dx, int dy, int dz) {
super.move(dx, dy); z += dz; totalMoves++;
}
}
the class variable totalMoves can be used only within the class Point; it is not
inherited by the subclass Point3d. A compile-time error occurs because method
move of class Point3d tries to increment totalMoves.
8.2.1.4 Accessing Members of Inaccessible Classes
Even though a class might not be declared public, instances of the class might be
available at run time to code outside the package in which it is declared by means
a public superclass or superinterface. An instance of the class can be assigned to
a variable of such a public type. An invocation of a public method of the object
referred to by such a variable may invoke a method of the class if it implements or
overrides a method of the public superclass or superinterface. (In this situation,
the method is necessarily declared public, even though it is declared in a class
that is not public.)
Consider the compilation unit:
package points;
public class Point {
public int x, y;
public void move(int dx, int dy) {
x += dx; y += dy;
}
}
and another compilation unit of another package:
DRAFT
package morePoints;
class Point3d extends points.Point {
public int z;
public void move(int dx, int dy, int dz) {
super.move(dx, dy); z += dz;
}
public void move(int dx, int dy) {
move(dx, dy, 0);
}
}