C# Inheritance and Polymorphism
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Questions and Answers

What is the purpose of the virtual method in a base class?

  • To hide methods and data from the derived class
  • To prevent overriding in a derived class
  • To overload methods in a derived class
  • To allow overriding in a derived class (correct)
  • What happens if a derived class does not override a virtual method?

  • The method is deleted from the derived class
  • The derived class can use the base class version (correct)
  • The derived class must override the method
  • The base class version is not accessible
  • What is an example of polymorphism in .NET?

  • Method overriding
  • Dynamic binding
  • Method overloading
  • The ToString() method (correct)
  • What is the difference between overriding and overloading?

    <p>Overriding has the same signature, while overloading has a different signature</p> Signup and view all the answers

    When is the selection of a method done in polymorphism?

    <p>At runtime</p> Signup and view all the answers

    What is the purpose of the virtual modifier in the Object class?

    <p>To imply that any class can override the ToString() method</p> Signup and view all the answers

    What is the term used to describe classes that depend on field names from parent classes?

    <p>Fragile</p> Signup and view all the answers

    What can a derived class do to a base class member?

    <p>Either override or hide it</p> Signup and view all the answers

    What is the purpose of the 'override' keyword in method overriding?

    <p>To provide a new definition for a method</p> Signup and view all the answers

    What is polymorphism?

    <p>Using the same method to indicate different implementations</p> Signup and view all the answers

    What is dynamic binding?

    <p>The selection of a method at runtime</p> Signup and view all the answers

    What is the purpose of the 'virtual' keyword in method overriding?

    <p>To make the method overridable</p> Signup and view all the answers

    What is the term used to describe the process of replacing a method defined at a higher level with a new definition?

    <p>Overriding</p> Signup and view all the answers

    What is the purpose of the 'abstract' keyword in method overriding?

    <p>To make the method abstract</p> Signup and view all the answers

    What is the term used to describe the process of using the same method to indicate different implementations?

    <p>Polymorphism</p> Signup and view all the answers

    What is the purpose of inheritance in object-oriented programming?

    <p>To create a new class from an existing class</p> Signup and view all the answers

    What is the purpose of marking a base instance method as virtual in C#?

    <p>To enable overriding of the method</p> Signup and view all the answers

    What happens if you mark a base instance method as virtual but not the derived instance method as override?

    <p>The compiler will generate an error</p> Signup and view all the answers

    How do you prevent overriding of a method in C#?

    <p>Don't use virtual on the base instance method</p> Signup and view all the answers

    What is the purpose of the base keyword in C#?

    <p>To access the parent class method or property</p> Signup and view all the answers

    What is the result of the following code: ScholarshipStudent freeStudent = new ScholarshipStudent(); freeStudent.Credits = 15;?

    <p>freeStudent's tuition will be set to 0</p> Signup and view all the answers

    What is the difference between method overriding and method shadowing in C#?

    <p>Method overriding is used to override the base method, while method shadowing is used to hide the base method</p> Signup and view all the answers

    What is the purpose of the override keyword in C#?

    <p>To override a base method</p> Signup and view all the answers

    What is the result of the following code: Student payingStudent = new Student(); payingStudent.Credits = 15;?

    <p>payingStudent's tuition will be set to a value based on the Credits property</p> Signup and view all the answers

    Study Notes

    Overriding Base Class Members

    • A virtual method can be overridden by a method with the same signature in a child class.
    • A derived class can override and hide methods and data from the base class.
    • A base class member that is not hidden by the derived class is visible in the derived class.

    Virtual Methods

    • The ToString() method uses the virtual modifier in the Object class, implying that any class can override it.
    • Overriding differs from overloading a method, as overridden methods have exactly the same signature, while overloaded methods have different signatures.

    Dynamic Binding and Polymorphism

    • Polymorphism uses dynamic binding, where the selection of the method is done at runtime.
    • Classes that depend on field names from parent classes are said to be fragile because they are prone to errors.

    Using the protected Access Specifier

    • The protected access specifier allows access to base class members from derived classes.

    Polymorphism and Overriding Base Class Members

    • A derived class contains data and methods defined in the original class.
    • Polymorphism is using the same method to indicate different implementations.
    • Examples of polymorphism include:
      • Different musical instruments having a Play() method.
      • Different vehicles having an Operate() method.
      • Different schools having a SatisfyGraduationRequirements() method.

    Overriding Methods

    • To override a method, use the override keyword in the derived class.
    • To prevent overriding of a method, don't use the virtual keyword.
    • It is possible to shadow a method in a derived class by marking it as new.
    • The CLR looks at the actual type of the object referred to.

    The ScholarshipStudent Class

    • The ScholarshipStudent class overrides the Credits property.
    • In the ScholarshipStudent class, the tuition is set to 0 when the Credits property is set.

    The DemoStudents Program

    • The DemoStudents program demonstrates the use of inheritance and polymorphism.
    • The program creates instances of Student and ScholarshipStudent classes and calls their methods.

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    Learn about inheritance in C# including virtual methods, overriding, and polymorphism with this quiz.

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