Factory Pattern

Factory Pattern 

Gamma Categorization: Creational Design Patten
Summary: When the object construction is complicated, needing multiple arguments, we should create a separate function (Factory Method) or class (Factory), which is responsible for the creation of the entire object.

Problem examples

Suport of multiple databases
Multiple data sources: Serial port, ethernet port, device driver
Diferent report types

Solution

Abstract class
Generalized interface
A Factory creates instances of the concrete classes

Sample Code

Problem: we need to create a Point object, that may be either Cartesian or Polar.

Factory Method Solution

public class Point

{

    private double x,  y;

    private Point (double x, double y)

    {

        this.x = x;

        this.y = y;

    }

    public static Point NewCartesianPoint(double x, double y)

    {

        return new Point(x, y);

    }

    public static Point NewPolarPoint(double rho, double theta)

    {

        return new Point(rho*Math.Cos(theta), rho*Math.Sin(theta));

    }

    public override string ToString() 

    {

        return $"x: {x}, y: {y}";

    }

}

Usage

var point = Point.NewCartesianPoint(10,20);

System.Console.WriteLine(point);

Factory Class Solution

public class PointFactory

{

    public static Point NewCartesianPoint(double x, double y)

    {

        return new Point(x, y);

    }

    public static Point NewPolarPoint(double rho, double theta)

    {

        return new Point(rho*Math.Cos(theta), rho*Math.Sin(theta));

    }

}

public class Point

{

    private double x,  y;

    public Point (double x, double y)

    {

        this.x = x;

        this.y = y;

    }

    public override string ToString() 

    {

        return $"x: {x}, y: {y}";

    }

}

Usage

var point = PointFactory.NewCartesianPoint(10,20);

System.Console.WriteLine(point);