Programming Pillars

1. Programming Pillars Inheritance Part 2

2. Lecture Overview • Abstract classes

3. Abstract Classes (Introduction) • Abstract classes define an interface • The implementation is either undefined or partially defined • It's not possible to create an instance of an abstract class • It's only possible to inherit from an abstract class • The purpose of abstract classes • Use to create generalized classes • Use to force standardized implementations of derived classes

4. Abstract Classes (Creating) • In the abstract class, define the interface for the class • Declare an abstract class or member with the abstract keyword in the class declaration

5. Abstract Classes (Using) • Define the implementation in the derived class • A derived class can inherit from an abstract classA derived class must implement all abstract members • (those declared as abstract) • A derived class can inherit members implemented in the abstract class

6. Abstract Classes (Example 1) • Cryptography uses standard algorithms to encrypt and decrypt messages • There are different cryptographic algorithms • DES, RC2, Rijndael, TripleDES • They all “work” the same way • They are all symmetric algorithms • The SymmetricAlgorithm class is the abstract class for all symmetric cryptographic algorithms

7. Abstract Classes (Example 1)

8. Abstract Classes (Example 2) • Declare an abstract class named person public abstract class Person {} • Declare an abstract method named public abstract bool SetID(intargID); • Note that the method has NO implementation

9. Implementing an Abstract Method (Example) • Use the override keyword to declare the implementation of an abstract method public override bool SetID( int argID) { RNumberHidden = argID; }

10. Prohibiting Inheritance • A sealed class is a class that cannot be inherited • Declare sealed classes with the sealed keyword • The string class is not inheritable