Inheritance and Polymorphism ABC programming lesson Inheritance and Polymorphism  Welcome to the module Inheritance and Polymorphism.  Inheritance is a process of creating a new class from an existing class.  Inheritance allows you to inherit attributes and methods of the base class in the newly created class.  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  Inheritance specifies an “is a kind of" relationship  Inheritance is a class relationship  New classes specialize existing classes Musician Musician Violin Player Violin Player Base class Derived class Generalization Specialization Is this a good example of inheritance ? 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 Implementing Inheritance  Just need to insert a colon after the name of the derived class followed by the name of the base class.  The derived class can now inherit all non-private methods and attributes of the base class. Example of Inheritance Animal Animal Cat 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 [...]... 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 A B B C C Example of polymorphism in C# Compile-time and Run-time Polymorphism  Compile-time Polymorphism     Implemented... 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... Compile-time and Run-time Polymorphism  Compile-time Polymorphism     Implemented through method overloading Executed at the compile-time Referred to as static polymorphism Run-time Polymorphism    Implemented through method overriding Executed at run-time Referred to as dynamic polymorphism ... 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,... 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 ... declaration Constructor Chaining Parent Parent F1 F1 F2 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..."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... 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 . Inheritance and Polymorphism ABC programming lesson Inheritance and Polymorphism  Welcome to the module Inheritance and Polymorphism.  Inheritance is a process of. on their parameters and data types.  In this module, you will learn about:  Implementing Inheritance  Method Overriding  Sealed Classes  Polymorphism #1 - Implementing Inheritance  Explain. 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