Definition

Separate the construction of a complex object from its representation so that the same construction process can create different representations, which allows for the step-by-step creation of complex objects using the correct sequence of action.

This pattern is used when a complex object that needs to be created is constructed by constituent parts that must be created in the same order or by using a specific algorithm.

Components

Builder：Interface for creating the actual products. Each step is an abstract method.
ConcreteBuilder：Implementation for builder.
Director：represent class that controls algorithm used for creation of complex object.
Product：complex object that is being built.

Builder Pattern UML

Code

public class DirectorCashier
{
    public void BuildFood(Builder builder)
    {
        builder.BuildPart1();
        builder.BuildPart2();
    }
}

public abstract class Builder
{
    public abstract void BuildPart1();

    public abstract void BuildPart2();

    public abstract Product GetProduct();
}

public class ConcreteBuilder1 : Builder
{
    protected Product _product;
    public ConcreteBuilder1()
    {
        _product = new Product();
    }
        
    public override void BuildPart1()
    {
        this._product.Add("Hamburger", "2");
    }
        
    public override void BuildPart2()
    {
        this._product.Add("Drink", "1");
    }

    public override Product GetProduct()
    {
        return this._product;
    }
}

public class Product
{
    public Dictionary<string, string> products = new Dictionary<string, string>();
        
    public void Add(string name, string value)
    {
        products.Add(name, value);
    }
        
    public void ShowToClient()
    {
        foreach (var p in products)
        {
            Console.WriteLine($"{p.Key} {p.Value}");
        }
    }
}

public class BuilderPatternRunner : IPattterRunner
{
    public void RunPattern()
    {
        var Builder1 = new ConcreteBuilder1();
        var Director = new DirectorCashier();

        Director.BuildFood(Builder1);
        Builder1.GetProduct().ShowToClient();
    }
}