Understanding the Strategy Design Pattern

Introduction to the Strategy Design Pattern

The Strategy Design Pattern is a behavioral design pattern that enables selecting an algorithm’s behavior at runtime. Instead of implementing a single algorithm directly, the code receives runtime instructions specifying which of a family of methods to use.

Key Concepts

• Strategy Interface: This defines a common interface for all supported algorithms. Any algorithm that implements the interface can be used interchangeably by the client that utilizes the strategies.
• Concrete Strategies: These are classes that implement the Strategy interface, providing specific behaviors.
• Context: A class that contains a reference to a Strategy object. The context delegates the work to the strategy object instead of executing its own algorithm.

Benefits

• Flexibility: Easily switch between different algorithms used by an object at runtime.
• Decoupling: The high level of decoupling between the context and the strategies allows for better manageability and scalability.
• Open/Closed Principle: You can introduce new strategies without changing the context’s code, adhering to this SOLID principle.

Example in Code

Here’s how you might implement the Strategy Pattern in C# for a simple application that can switch its behavior at runtime:

// Strategy interface
public interface IStrategy
{
    void Execute();
}

// Concrete strategies
public class ConcreteStrategyA : IStrategy
{
    public void Execute()
    {
        Console.WriteLine("Executing Strategy A");
    }
}

public class ConcreteStrategyB : IStrategy
{
    public void Execute()
    {
        Console.WriteLine("Executing Strategy B");
    }
}

// Context class
public class Context
{
    private IStrategy _strategy;

    public Context(IStrategy strategy)
    {
        this._strategy = strategy;
    }

    public void SetStrategy(IStrategy strategy)
    {
        this._strategy = strategy;
    }

    public void ExecuteStrategy()
    {
        _strategy.Execute();
    }
}

// Example usage
class Program
{
    static void Main(string[] args)
    {
        var context = new Context(new ConcreteStrategyA());
        context.ExecuteStrategy();
        context.SetStrategy(new ConcreteStrategyB());
        context.ExecuteStrategy();
    }
}