Programmer's Guide to Java™ Certification, A: A Comprehensive Primer, Second Edition

6. Object-oriented Programming

6.1

(a) and (b) The extends clause is used to specify that a class extends another class. A subclass can be declared abstract regardless of whether the superclass was declared abstract. Private, overridden, and hidden members from the superclass are not inherited by the subclass. A class cannot be declared both abstract and final, since an abstract class needs to be extended to be useful and a final class cannot be extended. The accessibility of the class is not limited by the accessibility of its members. A class with all the members declared private can still be declared public.

6.2

(b) and (e) Inheritance defines an is-a relation. Aggregation defines a has-a relation. The Object class has a public method named ...