Object-Oriented Concepts - SCJP Sun Certified Programmer for Java Platform SE6 - page 396

5. public class RotaryPhone extends Phone {
6. private int number;
7.
8. public RotaryPhone(int n, int e, String r) {
9. super(n, e, r);
10. this.number = super.number;
11. }
12.
13. public void placeCall(int numberToDial) {
14. super.placeCall(numberToDial);
15. System.out.println(“Using ring tone “ + ringTone);
16. }
17. }
The RotaryPhone class makes some valid and invalid attempts at accessing the members
of Phone :
Line 9 invokes the protected constructor of Phone , which is valid because
RotaryPhone is a child of Phone .
Line 10 is valid because the number field in Phone is public and therefore accessible to
any other class.
Line 14 does not compile because the placeCall method has default access and
RotaryPhone is not in the same package as Phone .
Line 15 does not compile because ringTone is private in Phone and therefore not
accessible outside of the Phone class.
Attempting to compile RotaryPhone generates the following compiler errors:
RotaryPhone.java:14: placeCall(int) is not public in
com.sybex.demos.Phone; cannot be accessed from outside package
super.placeCall(numberToDial);
^
RotaryPhone.java:15: ringTone has private access in
com.sybex.demos.Phone
System.out.println(“Using ring tone “ + ringTone);
^
2 errors
In the real world you would implement tight encapsulation, so the number
field of Phone would not be public . However, the Phone class is meant
to demonstrate the effect of the access modifiers, and you can expect
exam questions that contain classes like Phone that do not follow good OO
design but instead are testing your knowledge of a specific Java concept.