Inheritance and Polymorphism - ABC programming lesson ppt

"protected " Access Modifier Protected variables or methods are accessed only by:  The class in which they are declared  Derived class  Specified using the protected keyword... " new

Inheritance and Polymorphism

ABC programming lesson

Inheritance and Polymorphism

 Welcome to the module Inheritance and

 Polymorphism is a feature of OOP that allows the data members of a class to behave

differently based on their parameters and data types.

 In this module, you will learn about:

 Implementing Inheritance

 Method Overriding

 Sealed Classes

 Polymorphism

#1 - Implementing Inheritance

 Explain the concept of inheritance

 Describe how to implement inheritance in C#.

 State and explain the protected access modifier.

 State and explain the base keyword.

 State and explain the new keyword.

 Describe how to inherit constructors.

 Inheritance specifies an “is a kind of" relationship

 Inheritance is a class relationship

 New classes specialize existing classes

Musician

Violin Player

Violin Player

Purpose of Inheritance

 Reusability

 Reuse common methods and attributes among classes without recreating them.

 Use the same code in different

applications with little or no

changes.

 Generalisation

 Specialisation

 Extension

Example of Inheritance

Animal

Cat

"protected " Access Modifier

 Protected variables or methods are accessed only by:

 The class in which they are declared

 Derived class

 Specified using the protected keyword.

" base " Keyword

 Like “ super ” in Java

 Access the variables and methods of the base class from the derived class.

 Cannot use the base keyword for invoking the static methods of the base class.

Example of Using " base " Keyword

" new " Keyword

 As a modifier to hide the methods or variables of the base class that are inherited in the derived class.

Example of " new " Keyword

Constructor Inheritance

 In C#, cannot inherit constructors like inherit methods

 The instance of the derived class will always first invoke the

constructor of the base class followed by the constructor of the derived class.

 Can explicitly invoke the base class constructor by using the base

keyword in the derived class constructor declaration

Constructor Chaining

Parent

F1

F2

Constructor Chaining

Rules for Constructors (MUST be clear and remember)

 A default constructor will be automatically generated by the compiler

if no constructor is specified within the class.

 The default constructor is ALWAYS a no-arg constructor.

 If there is a constructor defined in the class, the default constructor is

no longer used.

 If you don’t explicitly call a base class constructor in a derived class constructor, the compiler attempts to silently insert a call to the base class’s default constructor before executing the code in the derived class constructor

Compiler-Generated Constructor Code

Can you see the Bugs?

How to fixed

Explicitly invoke the base class constructor

#2 - Method Overriding

 Define method overriding.

 Explain virtual and override keywords.

Method Overriding

 Derived class to override or redefine the methods of the base class.

 A method that is intended to be overridden is called a virtual method

 The method implemented in the derived class from the base class is known as the Overridden Base Method.

Implementing Method Overriding

 Using appropriate "virtual" and "override" Keywords

 To override a particular method of the base class in the derived class:

 In the base class, declare the method using the “virtual” keyword.

 In the derived class, declare the inherited virtual method using the “override” keyword

Example of Implementing Method Overriding

Method Overriding Remarks

 The overridden base method must have the same signature as the virtual method

 Cannot override a non-virtual or static method.

 Both the override method and the virtual method must have the same access level modifier.

Declaring new Methods

Calling the Base Class Method

#3 - Sealed Classes

 Define sealed classes in C#

 Describe the purpose of sealed classes.

Sealed Classes

 Class that prevents inheritance.

 Like “final” class in Java

 To declare, use sealed keyword before class keyword.

 If a class tries to derive a sealed class, the C# compiler generates an error.

Purpose of Sealed Classes

 Ensure Security

 Protect from Copyright Problems

 Prevent Inheritance

Using Sealed Class Guidelines

 If overriding the methods of a class might result in in unexpected functioning of the class

 To prevent any third party from modifying your class

#4 - Polymorphism

 Define polymorphism in C#

 Explain how to implement polymorphism

 Describe compile and run-time polymorphism

Define polymorphism in C#

 Polymorphism means existing in multiple forms

 The ability of an entity to behave differently in different situations

 Polymorphism allows methods to function differently based on the parameters and their data types

 Implement polymorphism in C# through:

 Method overloading (Compile-time Polymorphism)

 Method overriding (Run-time Polymorphism)

Example of polymorphism in C#

A B C

Example of polymorphism in C#

Compile-time and Run-time Polymorphism

 Compile-time Polymorphism

 Implemented through method overloading

 Executed at the compile-time

 Referred to as static polymorphism

That’s about all for today!