Object Concepts in C# Class, object, attribute, method, message, instance, encapsulation, polymorphism, inheritance, association, persistence, Generalization/specialization, subclass, superclass

Data Encapsulation Example

class EdClass { [STAThread] static void Main(string[] args) { EncapsulatedData ed = new EncapsulatedData(); Console.WriteLine(ed.X()); } Class Method Object Instantiation Message to method X of the EncapsulatedData Object referenced by ed Object Reference Method Attribute For Compiler Storage Class Return Type

Data Encapsulation Example public class EncapsulatedData { private int x; public EncapsulatedData() { x = 25; } public int X() { return x; } public int X(int type) { return x; } Encapsulated Data (private to class) Class Constructor Overloaded method X Scope Modifier

Data Encapsulation Example Execution Yields:

Inheritance and Polymorphism

class InheritanceApplication { [STAThread] static void main(string[] args) { Account acc = new Account(); // create a new Account acc.setBalance(1000); Console.Write("Account interest = "); Console.WriteLine(acc.calcInterest()); acc = new MoneyMarket(); // create a new MoneyMarket object acc.setBalance(1000); Console.Write("MoneyMarket interest = "); Console.WriteLine(acc.calcInterest()); acc = new Savings(); // create a new Savings object acc.setBalance(1000); Console.Write("Savings interest = "); Console.WriteLine(acc.calcInterest()); } Create an object of type Account, MoneyMarket & Savings then calc and display interest Late Binding Polymorphic Behavior

Inheritance and Polymorphism /// /// Account is a superclass used as a base for all types of accounts. /// public class Account { protected double interestRate; protected double balance; public Account() // public constructor { balance = 0.0; interestRate = 0.05; } public virtual double calcInterest() // used to calculate interest { if (balance != 0.0) return balance * (1.0 + interestRate); else return 0.0; } public void setBalance(double bal) // used to set the { balance = bal; } Attributes Superclass Virtual Method that will be overriden Superclass Annual Compounding

Inheritance and Polymorphism public class MoneyMarket : Account // MoneyMarket is derived from the base class { public MoneyMarket() // default constructor which on the base class : base() { } public override double calcInterest() // interest semiannually compounding { if (balance != 0.0) return balance * Math.Pow((1.0 + interestRate/2.0), 2); else return 0.0; } Subclass Inherited From Account Overridden Base Class Method MoneyMarket is a Specialization of Account Note Semi-annual compounding

Inheritance and Polymorphism public class Savings : Account // Savings class inherits from Account { public Savings() // default constructor which call the Account { : base() } public override double calcInterest() // monthly compounding { if (balance != 0.0) return balance * Math.Pow((1.0 + interestRate/12.0), 12); else return 0.0; } Note monthly compounding

Inheritance and Polymorphism An Account object reference was used for each, but the correct interest method was called for each. This is Polymorphism.