protected Members

Chapter 8 discussed access modifiers public and private. A class's public members are accessible wherever the program has a reference to an object of that class or one of its subclasses. A class's private members are accessible only from within the class itself. A superclass's private members are not inherited by its subclasses. In this section, we introduce access modifier protected. Using protected access offers an intermediate level of access between public and private. A superclass's protected members can be accessed by members of that superclass, by members of its subclasses and by members of other classes in the same package (i.e., protected members also have package access).

All public and protected superclass members retain their original access modifier when they become members of the subclass (i.e., public members of the superclass become public members of the subclass, and protected members of the superclass become protected members of the subclass).

Subclass methods can refer to public and protected members inherited from the superclass simply by using the member names. When a subclass method overrides a superclass method, the superclass method can be accessed from the subclass by preceding the superclass method name with keyword super and a dot (.) separator. We discuss accessing overridden members of the superclass in Section 9.4.

Software Engineering Observation 9.1

Methods of a subclass cannot directly access private members of their superclass. A subclass can change the state of private superclass instance variables only through non-private methods provided in the superclass and inherited by the subclass.

Software Engineering Observation 9.2

Declaring private instance variables helps programmers test, debug and correctly modify systems. If a subclass could access its superclass's private instance variables, classes that inherit from that subclass could access the instance variables as well. This would propagate access to what should be private instance variables, and the benefits of information hiding would be lost.

Introduction to Computers, the Internet and the World Wide Web

Introduction to Java Applications

Introduction to Classes and Objects

Control Statements: Part I

Control Statements: Part 2

Methods: A Deeper Look


Classes and Objects: A Deeper Look

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism

GUI Components: Part 1

Graphics and Java 2D™

Exception Handling

Files and Streams


Searching and Sorting

Data Structures



Introduction to Java Applets

Multimedia: Applets and Applications

GUI Components: Part 2



Accessing Databases with JDBC


JavaServer Pages (JSP)

Formatted Output

Strings, Characters and Regular Expressions

Appendix A. Operator Precedence Chart

Appendix B. ASCII Character Set

Appendix C. Keywords and Reserved Words

Appendix D. Primitive Types

Appendix E. (On CD) Number Systems

Appendix F. (On CD) Unicode®

Appendix G. Using the Java API Documentation

Appendix H. (On CD) Creating Documentation with javadoc

Appendix I. (On CD) Bit Manipulation

Appendix J. (On CD) ATM Case Study Code

Appendix K. (On CD) Labeled break and continue Statements

Appendix L. (On CD) UML 2: Additional Diagram Types

Appendix M. (On CD) Design Patterns

Appendix N. Using the Debugger

Inside Back Cover

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Java(c) How to Program
Java How to Program (6th Edition) (How to Program (Deitel))
ISBN: 0131483986
EAN: 2147483647
Year: 2003
Pages: 615
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