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Design Patterns(C#): Basic example Strategy pattern

In this example I´m going to explane the strategy pattern. With this example you can do a calculation with two numbers (-/+) and expand the number of operators (/, *, etc.).

First create a interface which defines the interface of the operator classes. For this example an operator can only calculate two values.

//The interface for the strategies
public interface ICalculateInterface
//define method
int Calculate(int value1, int value2);

Next create the operators (strategies) Minus (which subtract value 2 from value 1) and Plussus (which addition value 1 with value 2). The classes need to inherit from the interface ICalculateInterface.

//Strategy 1: Minus
class Minus : ICalculateInterface
public int Calculate(int value1, int value2)
//define logic
return value1 - value2;

//Strategy 2: Plussus
class Plussus : ICalculateInterface
public int Calculate(int value1, int value2)
//define logic
return value1 + value2;

At last we need to create a Client that will execute the strategy.

//The client
class CalculateClient
private ICalculateInterface calculateInterface;

//Constructor: assigns strategy to interface
public CalculateClient(ICalculateInterface strategy)
calculateInterface = strategy;

//Executes the strategy
public int Calculate(int value1, int value2)
return calculateInterface.Calculate(value1, value2);

Now we have two operators (minus & plussus) and a client (CalculateClient) that can execute the operators. Let’s test the code. Create a new webapplication, console app or something else that can write output. For this example I will use a webpage.

Initialize a new CalculateClient with argument operator Minus of Plussus and Calculate two values.

protected void Page_Load(object sender, EventArgs e)
CalculateClient minusClient = new CalculateClient(new Minus());
Response.Write("<br />Minus: " + minusClient.Calculate(7, 1).ToString());

CalculateClient plusClient = new CalculateClient(new Plussus());
Response.Write("<br />Plussus: " + plusClient.Calculate(7, 1).ToString());

This code will give the following output.

<br />Minus: 6
<br />Plussus: 8

The great thing about this pattern is that you can easily add new opertators (strategies) to your code.


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About the Author

About the Author: Pieter is Technical Marketing Manager for Sitecore Netherlands and owner of He has more than ten years experience with software developing in multiple programming languages and with different Content Management Systems. Before joining Sitecore Pieter was a lead developer for multiple Sitecore and .Net projects, he joined Sitecore in 2011 as an Solution Architect in The Netherlands, after two years as an Solution Architect he joined the Technical Marketing department. In the role as Techinical Marketing Manager he is responsible for the Global MVP program and the Sitecore technical branding strategy. You can follow Pieter on twitter: @pieterbrink123 or Google+ .


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There Are 7 Brilliant Comments

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  1. raja says:

    very Nice Explanation

  2. Cau Silvestrini says:

    Thanks man, just what I was looking for.
    It couldn’t be any clearer! 🙂

  3. Prashant Vedpathak says:

    That was good. Could you please provide remaining frequently used Design patterns examples. It would be very easy for all of them to understand such simple learning. Thank you for this post.

  4. Dinesh says:

    Nice explanation.

  5. Raja says:

    I think this is dependency injection not strategy pattern

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