Controlling Access to Members

The access modifiers public and private control access to a class's variables and methods. (In Section 9.15 and Chapter 10, we will introduce the additional access modifiers internal and protected, respectively.) As we stated in Section 9.2, the primary purpose of public methods is to present to the class's clients a view of the services the class provides (the class's public interface). Clients of the class need not be concerned with how the class accomplishes its tasks. For this reason, a class's private variables and methods (i.e., the class's implementation details) are not directly accessible to the class's clients.

Figure 9.3 demonstrates that private class members are not directly accessible outside the class. Lines 911 attempt to access directly private instance variables hour, minute and second of Time1 object time. When this application is compiled, the compiler generates error messages stating that these private members are not accessible. [Note: This application assumes that the Time1 class from Fig. 9.1 is used.]

Figure 9.3. Private members of class Time1 are not accessible.

 1 // Fig. 9.3: MemberAccessTest.cs
 2 // Private members of class Time1 are not accessible.
 3 public class MemberAccessTest
 4 {
 5 public static void Main( string[] args )
 6 {
 7 Time1 time = new Time1(); // create and initialize Time1 object
 9 time.hour = 7; // error: hour has private access in Time1
10 time.minute = 15; // error: minute has private access in Time1
11 time.second = 30; // error: second has private access in Time1
12 } // end Main
13 } // end class MemberAccessTest

Common Programming Error 9 1

An attempt by a method that is not a member of a class to access a private member of that class is a compilation error.

Notice that members of a classfor instance, methods and instance variablesdo not need to be explicitly declared private. If a class member is not declared with an access modifier, it has private access by default. We always explicitly declare private members.

Referring to the Current Object s Members with the this Reference



    Introduction to Computers, the Internet and Visual C#

    Introduction to the Visual C# 2005 Express Edition IDE

    Introduction to C# Applications

    Introduction to Classes and Objects

    Control Statements: Part 1

    Control Statements: Part 2

    Methods: A Deeper Look


    Classes and Objects: A Deeper Look

    Object-Oriented Programming: Inheritance

    Polymorphism, Interfaces & Operator Overloading

    Exception Handling

    Graphical User Interface Concepts: Part 1

    Graphical User Interface Concepts: Part 2


    Strings, Characters and Regular Expressions

    Graphics and Multimedia

    Files and Streams

    Extensible Markup Language (XML)

    Database, SQL and ADO.NET

    ASP.NET 2.0, Web Forms and Web Controls

    Web Services

    Networking: Streams-Based Sockets and Datagrams

    Searching and Sorting

    Data Structures



    Appendix A. Operator Precedence Chart

    Appendix B. Number Systems

    Appendix C. Using the Visual Studio 2005 Debugger

    Appendix D. ASCII Character Set

    Appendix E. Unicode®

    Appendix F. Introduction to XHTML: Part 1

    Appendix G. Introduction to XHTML: Part 2

    Appendix H. HTML/XHTML Special Characters

    Appendix I. HTML/XHTML Colors

    Appendix J. ATM Case Study Code

    Appendix K. UML 2: Additional Diagram Types

    Appendix L. Simple Types


    Visual C# How to Program
    Visual C# 2005 How to Program (2nd Edition)
    ISBN: 0131525239
    EAN: 2147483647
    Year: 2004
    Pages: 600

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