Java Reference
In-Depth Information
Example 8.2-4. Inheritance of
private
Class Members
class Point {
int x, y;
void move(int dx, int dy) {
x += dx; y += dy; totalMoves++;
}
private static int totalMoves;
void printMoves() { System.out.println(totalMoves); }
}
class Point3d extends Point {
int z;
void move(int dx, int dy, int dz) {
super.move(dx, dy); z += dz; totalMoves++; // error
}
}
Here, the class variable
totalMoves
can be used only within the class
Point
; it is not in-
herited by the subclass
Point3d
. A compile-time error occurs because method move of
class
Point3d
tries to increment
totalMoves
.
Example 8.2-5. Accessing Members of Inaccessible Classes
Even though a class might not be declared
public
, instances of the class might be avail-
able 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:
