Decorator pattern implementation

Question

Trying to implement the decorator pattern in C# from the code in the \"Head First Design Patterns\" book (written in Java).

I am just starting out with C# and am the

Answer 1

Change new to override. Also, m_description should be protected.

Answer 2

You have declared the Cost() method of Mocha as new instead of override. See here the difference: http://blogs.msdn.com/b/csharpfaq/archive/2004/03/12/what-s-the-difference-between-code-override-code-and-code-new-code.aspx

Answer 3

This is how should your code look.

public abstract class Beverage
{
    protected string m_description = "Unknown Beverage";

    public virtual string GetDescription()
    {
        return m_description;
    }

    public abstract double Cost();
}

public abstract class CondimentDecorator : Beverage
{
}

public class Espresso : Beverage
{
    public Espresso()
    {
        m_description = "Espresso";
    }

    public override double Cost()
    {
        return 1.99;
    }
}

public class HouseBlend : Beverage
{
    public HouseBlend()
    {
        m_description = "House Blend Coffe";
    }

    public override double Cost()
    {
        return 0.89;
    }
}

public class DarkRoast : Beverage
{
    public DarkRoast()
    {
        m_description = "Dark Roast";
    }

    public override double Cost()
    {
        return 0.99;
    }
}

public class Mocha : CondimentDecorator
{
    Beverage beverage;

    public Mocha(Beverage beverage)
    {
        this.beverage = beverage;
    }

    public override string GetDescription()
    {
        return beverage.GetDescription() + ", Mocha";
    }

    public override double Cost()
    {
        return 0.20 + beverage.Cost();
    }
}

public class Soy : CondimentDecorator
{
    Beverage beverage;

    public Soy(Beverage beverage)
    {
        this.beverage = beverage;
    }

    public override string GetDescription()
    {
        return beverage.GetDescription() + ", Soy";
    }

    public override double Cost()
    {
        return 0.15 + beverage.Cost();
    }
}

public class Whip : CondimentDecorator
{
    Beverage beverage;

    public Whip(Beverage beverage)
    {
        this.beverage = beverage;
    }

    public override string GetDescription()
    {
        return beverage.GetDescription() + ", Whip";
    }

    public override double Cost()
    {
        return 0.10 + beverage.Cost();
    }
}