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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);

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