Polymorphism

4.17. What is Polymorphisms?

Polymorphisms is a generic term that means 'many shapes'. More precisely Polymorphisms means the ability to request that the same operations be performed by a wide range of different types of things.

At times, I used to think that understanding Object Oriented Programming concepts have made it difficult since they have grouped under four main concepts, while each concept is closely related with one another. Hence one has to be extremely careful to correctly understand each concept separately, while understanding the way each related with other concepts.

In OOP the polymorphisms is achieved by using many different techniques named method overloading, operator overloading and method overriding,

4.18. What is Method Overloading?

The method overloading is the ability to define several methods all with the same name.

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public class MyLogger
{
  public void LogError(Exception e)
  {
      // Implementation goes here
  }

  public bool LogError(Exception e, string message)
  {
      // Implementation goes here
  }
}

4.19. What is Operator Overloading?

The operator overloading (less commonly known as ad-hoc polymorphisms) is a specific case of polymorphisms in which some or all of operators like +, - or == are treated as polymorphic functions and as such have different behaviors depending on the types of its arguments.

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public class Complex
{
  private int real;
  public int Real
  { get { return real; } }

  private int imaginary;
  public int Imaginary
  { get { return imaginary; } }

  public Complex(int real, int imaginary)
  {
      this.real = real;
      this.imaginary = imaginary;
  }

  public static Complex operator +(Complex c1, Complex c2)
  {
      return new Complex(c1.Real + c2.Real, c1.Imaginary + c2.Imaginary);
  }
}

I above example I have overloaded the plus operator for adding two complex numbers. There the two properties named Real and Imaginary has been declared exposing only the required “get” method, while the object’s constructor is demanding for mandatory real and imaginary values with the user defined constructor of the class.

4.20. What is Method Overriding?

Method overriding is a language feature that allows a subclass to override a specific implementation of a method that is already provided by one of its super-classes.

A subclass can give its own definition of methods but need to have the same signature as the method in its super-class. This means that when overriding a method the subclass's method has to have the same name and parameter list as the super-class's overridden method.

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using System;
public class Complex
{
  private int real;
  public int Real
  { get { return real; } }

  private int imaginary;
  public int Imaginary
  { get { return imaginary; } }

  public Complex(int real, int imaginary)
  {
      this.real = real;
      this.imaginary = imaginary;
  }

  public static Complex operator +(Complex c1, Complex c2)
  {
      return new Complex(c1.Real + c2.Real, c1.Imaginary + c2.Imaginary);
  }

  public override string ToString()
  {
      return (String.Format("{0} + {1}i", real, imaginary));
  }
}

In above example I have extended the implementation of the sample Complex class given under operator overloading section. This class has one overridden method named “ToString”, which override the default implementation of the standard “ToString” method to support the correct string conversion of a complex number.

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Complex num1 = new Complex(5, 7);
Complex num2 = new Complex(3, 8);

// Add two Complex numbers using the
// overloaded plus operator
Complex sum = num1 + num2;

// Print the numbers and the sum 
// using the overriden ToString method
Console.WriteLine("({0}) + ({1}) = {2}", num1, num2, sum);
Console.ReadLine();

4.21. What is a Use case?

A use case is a thing an actor perceives from the system. A use case maps actors with functions. Importantly, the actors need not be people. As an example a system can perform the role of an actor, when it communicate with another system.

In another angle a use case encodes a typical user interaction with the system. In particular, it:

• Captures some user-visible function.

• Achieves some concrete goal for the user.

A complete set of use cases largely defines the requirements for your system: everything the user can see, and would like to do. The below diagram contains a set of use cases that describes a simple login module of a gaming website.

4.22. What is a Class Diagram?

A class diagrams are widely used to describe the types of objects in a system and their relationships. Class diagrams model class structure and contents using design elements such as classes, packages and objects. Class diagrams describe three different perspectives when designing a system, conceptual, specification, and implementation. These perspectives become evident as the diagram is created and help solidify the design.

The Class diagrams, physical data models, along with the system overview diagram are in my opinion the most important diagrams that suite the current day rapid application development requirements.

UML Notations: