08 iec t1_s1_oo_ps_session_11

Object-Oriented Programming Using C#
Objectives

In this session, you will learn to:
Use abstract classes
Use sealed classes
Use interfaces
Implement the file input and output operations

Ver. 1.0 Session 11 Slide 1 of 16

Using Abstract Classes

C# enables you to create abstract classes that are used to
provide partial class implementation of an interface.
Abstract classes contain abstract methods, which can be
implemented by the derived class.
Polymorphism can be implemented by using abstract
classes and virtual functions.
There are certain rules governing the use of an abstraction
class:
Cannot create an instance of an abstract class.
Cannot declare an abstract method outside an abstract class.
Cannot be declared sealed.


Using Abstract Methods

Abstract methods are methods without any body.
The implementation of an abstract method is done by the
derived class.
When a derived class inherits the abstract method form the
abstract class, it must override the abstract methods. This
requirement is enforced at compile time, and is also called
dynamic polymorphism.
The syntax for using the abstract method is as follows:
[access-modifiers] abstract return-type method
name (parameters]);
The abstract method is declared by adding the abstract
modifier to the method.


Using Virtual Functions

• When you have a function defined in a class which you
want to allow to be implemented by the inherited classes,
you can use virtual function.
• The virtual function could be implemented by the
inherited classes in their own way and the call to the
method is decided at the run time.


Using Sealed Classes

• You could restrict users form inheriting the class by sealing
the class using the sealed keyword.
• The sealed keyword tells the compiler that the class is
sealed, and therefore, cannot be extended.
• The following is an example of a sealed class:
sealed class FinalClass
{
private int x;
public void Method1()
{
}
}
A method can also be sealed and in that case the method
cannot be overridden.


Using Interfaces

Interfaces define properties, methods, and events, which
are known as the members of the interface.
Interfaces are fully supported by C#.
Interfaces are used when a standard structure of methods is
to be followed by the classes, and where classes will
implement the functionality.
Interfaces separate the definition of objects from their
implementation so that the objects can evolve without the
risk of introducing incompatibility in existing applications.


Working with Interfaces

• Working with interfaces includes interface declaration and
implementation of interface by the classes.
• You can declare interfaces using the interface keyword.
• Interface statements are public, by default.
• You can declare only methods, functions, and properties in
interfaces. You cannot declare a variable in interfaces.
• Interfaces declare methods, which are implemented by
classes. A class can inherit from single class but can
implement form multiple interfaces.


Inheriting Interfaces

A class or a structure that implements interfaces also
implements the base interfaces of the inherited interface.


Demo: Order-Processing System Using Abstract Classes

Problem Statement:
Furniture and Fittings Company (FFC) manufactures domestic
furniture. Customers provide their specifications to the
company for the furniture they want. To cope with the received
customer’s orders, FFC decides to computerize the
order-processing system. The system should accept the values
of furniture items, such as a bookshelf and a chair. You need
to develop the hierarchy of these items.


Demo: Order-Processing System Using Abstract Classes (Contd.)

Solution:
To create a console based application for FFC, you need to
perform the following tasks:
1. Create a console-based application.
2. Build and execute an application.


Implementing the File Input and Output Operations

• The stream is a sequence of bytes traveling from a source
to a destination over a communication path.
• The two basic streams used are the input and output
streams.
• An input stream is used for a read operation and an output
stream is used for performing a write operation.
• The System.IO namespace includes various classes, which
are used to perform operations, such as file creation, file
deletion, and the read-write operations to files.


FileStream Class

• To open an existing file or to create a new file, you need to
create an object of type FileStream.
• Consider the following syntax for creating the object of type
FileStream:
FileStream <object name>=new FileStream(<file
Name>,<FileMode Enumerator>,<File Access
Enumerator>,<FileShare Enumerator>);


FileStream Class (Contd.)

• FileMode enumerator defines various methods for opening
files.
• The FileMode enumerator parameter is specified in many
constructors for the FileStream.
• The parameters to FileMode checks whether a file is
overwritten, created, or opened.
• FileAccess enumerator indicates whether you want to read
data from the file, write to the file, or perform both the
operations.
• The members of the FileAccess enumerator are Read,
ReadWrite, and Write.


FileStream Class (Contd.)

The FileShare enumerator contains constants for
controlling the kind of access that the other FileStream
constructors can have to the same file.
A typical use of this enumeration is to define whether two
different applications can simultaneously read from the
same file.


Summary

In this session, you learned that:
– An abstract superclass is a conceptual class that does not
exist in real world but acts as a base from which other classes
inherit properties behavior.
– A sealed class tells the compiler that the class cannot be
extended further. You cannot derive a class from a sealed
class.
– An interface defines properties, methods, and events. The
properties, methods, and events that are defined in the
interface are known as the members of the interface.
– A stream is an abstraction of a sequence of bytes traveling
from a source to a destination over a communication path.


Summary (Contd.)

– The two basic streams used are the input and output streams.
An input stream is used for a read operation and an output
stream is used for performing a write operation.
– Most file input/output (I/O) support in the .NET Framework is
implemented in the System.IO namespace. You can use the
FileStream class in the System.IO namespace to read
from, to write, and to close files.
– The FileStream class inherits from the abstract class
Stream.


08 iec t1_s1_oo_ps_session_11

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