1. ASP.NET Programming with C# and SQL Server First Edition
Chapter 10
Developing Object-Oriented C# Programs

2. Objectives In this chapter, you will:
Study object-oriented programming concepts
Define custom classes
Declare class fields
Work with class methods
ASP.NET Programming with C# and SQL Server, First Edition

3. Introduction The programs written so far have been self-contained
Most of the code exists within a script section
Object-oriented programming allows you to use and create self-contained sections of code that can be reused without having to copy them
ASP.NET Programming with C# and SQL Server, First Edition

4. Introduction to Object-Oriented Programming
Object-oriented programming (OOP): refers to the creation of reusable software objects
Object: programming code and data that can be treated as an individual unit or component
Code that comprises an object is organized into classes
Objects may range from simple controls, such as a button, to entire programs
Objects are often designed to perform specific tasks
ASP.NET Programming with C# and SQL Server, First Edition

5. Introduction to Object-Oriented Programming (cont’d.)
Popular object-oriented programming languages include C++, Java, and Visual Basic
In many cases, objects written in one language can be used by programs written in another language
You only need to know how to access the methods and properties of those objects to use them
ASP.NET Programming with C# and SQL Server, First Edition

6. Understanding Encapsulation
Encapsulated objects: all code and required data are contained within the object itself
Usually within a single file
Interface: refers to the methods and properties that are required for a source program to communicate with an object
Objects can be thought of as “black boxes”
Users of the object can see only the methods and properties that you allow them to see
Example: handheld calculator
You do not need to know its inner workings to use it
ASP.NET Programming with C# and SQL Server, First Edition

7. Understanding Encapsulation (cont’d.)
Figure 10-1 Calculator interface
ASP.NET Programming with C# and SQL Server, First Edition

8. Using Objects in C# Programs
Object-oriented techniques will help you build more extensible code that is easier to reuse, modify, and enhance
Class: a template, or blueprint, that serves as the basis for creating new instances of objects from the class
Instantiation: the creation of an object from a class
A particular instance of an object inherits its methods and properties from the class from which it was created
ASP.NET Programming with C# and SQL Server, First Edition

9. Using Objects in C# Programs (cont’d.)
Syntax to instantiate an object from a class:
ClassName objectName = new ClassName();
Class constructors are used to initialize properties when an object is first instantiated
Many constructors accept arguments
Use a period to access the methods and properties of an object
Methods require a set of parentheses at the end of the method name, like functions
Methods can accept arguments
ASP.NET Programming with C# and SQL Server, First Edition

10. Using Objects in C# Programs (cont’d.)
Sample application: Central Valley Bakery Web site
Has four shopping categories: cakes, cookies, pies, and breads
Goal: develop a reusable class named ShoppingCart to handle the functionality of building and updating a shopping cart for a Web site
ShoppingCart class requires four fields for product information: productID, name, description, and price
ASP.NET Programming with C# and SQL Server, First Edition

11. Figure 10-2 Central Valley Bakery home page
ASP.NET Programming with C# and SQL Server, First Edition

12. Figure 10-3 Cakes product page after adding Web server controls
ASP.NET Programming with C# and SQL Server, First Edition

13. Defining Custom C# Classes
Data structure: a system for organizing data
Field: a variable defined within a class
Class members: the methods and fields defined in a class
Data members (or member variables): class variables
Function members (or member functions): the methods defined in a class
ASP.NET Programming with C# and SQL Server, First Edition

14. Defining Custom C# Classes (cont’d.)
After an object has been instantiated:
Class data members are called properties of the object
Class function members are called methods of the object
Classes are also called user-defined data types or programmer-defined data types
ASP.NET Programming with C# and SQL Server, First Edition

15. Defining Custom C# Classes (cont’d.)
Why use classes?
They help make complex programs easier to manage by logically grouping related methods and fields
They can be used to hide information that users of the class do not need to access
They provide an easy way to reuse code
Instances of class objects inherit class members from the class on which they are based, allowing you to build new classes based on existing classes
ASP.NET Programming with C# and SQL Server, First Edition

16. Working with Access Modifiers
Access modifiers: control a client’s access to classes, individual fields, methods and their members
There are five access modifiers in C#:
public
private
protected
internal
protected internal
The default value is internal
ASP.NET Programming with C# and SQL Server, First Edition

17. Working with Access Modifiers (cont’d.)
Table 10-1 C# access modifiers
ASP.NET Programming with C# and SQL Server, First Edition

18. Creating a Class Definition
Class definition: contains the class members that make up the class
Syntax:
accessModifier class ClassName {
//Class member definitions }
Class names should start with an uppercase letter
partial keyword: indicates that a class definition can be split across multiple files
ASP.NET Programming with C# and SQL Server, First Edition

19. Collecting Garbage
Garbage collection: the cleaning up, or reclaiming, of a member that is reserved by a program
C# knows when a program no longer needs a variable or object and automatically cleans up the memory for that program
Exception: open database connections must be closed by the program
ASP.NET Programming with C# and SQL Server, First Edition

20. Declaring Class Fields
A class definition requires the declaration of class fields
To design a class definition, you must understand the principle of information hiding
ASP.NET Programming with C# and SQL Server, First Edition

21. What Is Information Hiding?
Information hiding: any class members that client programs do not need to know about should be hidden
Information hiding gives an encapsulated object its “black box” capabilities
Users of the class see only the members of the class that you allow them to see
Reduces the complexity of the code that clients see
Prevents the accidental introduction of a bug into a program by other programmers
ASP.NET Programming with C# and SQL Server, First Edition

22. Using Access Modifiers with Fields
Class fields are declared like standard variables, except that an access modifier is included at the beginning of the declaration
It is good programming practice to assign an initial value to a field when it is declared
To access a field as an object property, append the property name to the object with a period
ASP.NET Programming with C# and SQL Server, First Edition

23. Serializing Objects
Serialization: the process of converting an object’s field into a string that can be stored for reuse
.NET Framework supports two types of serialization:
Binary serialization
XML serialization
Binary serialization: converts object properties to a binary format
Very efficient
Maintains the data types of the properties
Readable only by the .NET Framework
ASP.NET Programming with C# and SQL Server, First Edition

24. Serializing Objects (cont’d.)
XML serialization: converts object properties to XML
Does not maintain the data types of properties
Good for sharing the data with other applications
Must mark a class as serializable in order to serialize an object of that class
Add the Serializable attribute immediately above the class definition, surrounded by brackets []
Binary serialized objects are commonly stored in binary files on a local computer
ASP.NET Programming with C# and SQL Server, First Edition

25. Serializing Objects (cont’d.)
File stream: used for accessing a resource, such as a file
Input stream: reads data from a resource
Output stream: writes data to a resource
Response.Write() statements send data to an output stream (the Web browser window)
You must include the System.IO namespace before you can use the FileStream class
Use the Serialize() method of the BinaryFormatter class to serialize objects in binary format
ASP.NET Programming with C# and SQL Server, First Edition

26. Serializing Objects (cont’d.)
Use the Deserialize() method of the BinaryFormatter class to convert serialized data back into an object
Add the NonSerialized attribute in brackets before the declaration of any field in the class that does not have to be serialized
You can store a serialized object in session state
To deserialize, you must cast the session variable to the class from which the serialized object was created
ASP.NET Programming with C# and SQL Server, First Edition

27. Working with Class Methods
Methods perform most of the work in a class
Methods are usually declared as public or private
public methods can be called by anyone
private methods can be called only by other methods in the same class
Only methods that clients need to access should be declared as public
Include an access modifier before the method’s return type
ASP.NET Programming with C# and SQL Server, First Edition

28. Initializing with Constructor Methods
Constructor method: a special method that is called automatically when an object is instantiated from a class
Its name is the same as the class name
It is declared without a return type
Must have the public access modifier
Usually used to assign initial values to fields or to perform other initialization tasks
A class may have one or more constructor methods
ASP.NET Programming with C# and SQL Server, First Edition

29. Cleaning Up with Destructor Methods
Destructor method: called when the object is destroyed
Cleans up any resources allocated to an object
You cannot explicitly call a destructor method
It is called automatically by the C# garbage collection
Often used to close files or database connections
Destructor name is the same as the class name, but preceded by a tilde symbol (~)
No access modifier or return type is used
ASP.NET Programming with C# and SQL Server, First Edition

30. Writing Accessors
Accessor methods: public methods that a client can call to retrieve or modify the value of a field
Also called set or get methods
Set methods modify field values and accept parameters to pass in the new value for the field
Get methods retrieve field values
C# allows you to create accessors using properties
Properties: special methods that can be used as public data members to set and get field values
Defined using the reserved words get and set
ASP.NET Programming with C# and SQL Server, First Edition

31. Figure 10-5 Shopping Cart page after adding several items
ASP.NET Programming with C# and SQL Server, First Edition

32. Summary
An object is programming code and data that can be treated as an individual unit or component
Objects are encapsulated; all code and data are contained within the object itself
An interface refers to the methods and properties that are required for a source program to communicate with an object
A class is a template, or blueprint, that serves as the basis for new objects
When you create an object from a class, you are said to be instantiating the object
ASP.NET Programming with C# and SQL Server, First Edition

33. Summary (cont’d.)‏
An instance of an object inherits its methods and properties from the class on which it is based
A data structure is a system for organizing data
A field is a variable defined within a class
Methods and fields defined in a class are called class members
Classes help make complex programs easier to manage by logically grouping related methods and fields
Access modifiers control a client’s access to classes, data members, and function members
ASP.NET Programming with C# and SQL Server, First Edition

34. Summary (cont’d.)‏
Garbage collection refers to cleaning up, or reclaiming, memory that is reserved by a program
The principle of information hiding states that any class members that clients do not need to access or know about should be hidden
Fields are declared like standard variables, except that you must include an access modifier
Serialization is the process of converting an object’s fields into a string that can be stored for reuse
ASP.NET Programming with C# and SQL Server, First Edition

35. Summary (cont’d.)‏
A file stream is used for accessing a resource, such as a file, that you can read from and write to
Public methods can be called by anyone, while private methods can be called only by other methods in the same class
Only methods that clients need to access should be declared as public
A constructor method is a special method that is called automatically when an object is instantiated from a class
ASP.NET Programming with C# and SQL Server, First Edition

36. Summary (cont’d.)‏
Any resources allocated to an object are cleaned up by a destructor method after the object is destroyed
Accessor methods are public methods that a client can call to retrieve or modify the value of a field
C# allows you to create accessors using properties, which are special methods that can be used as public data members to set and get field values
ASP.NET Programming with C# and SQL Server, First Edition