装饰模式问题C#/ java

Question

我正在看这篇维基百科文章,无法理解这是怎么回事.有点沮丧只是通过查看它无法理解代码,我决定将代码移植到c#(我是.net,对不起家伙:)).只需要一些小修改(继承和扩展,基于超级等)并运行应用程序.令我惊讶的是,我得到了以下输出:

Cost: 1 Ingredient: Coffee
Cost: 1 Ingredient: Coffee
Cost: 1 Ingredient: Coffee
Cost: 1 Ingredient: Coffee

只是好奇,任何java开发都可以告诉我这里有什么不同以及为什么维基百科示例有效(如果它确实有效,就像它们所说的那样).

    namespace ConsoleApplication1
{
 class Program
 {
  static void Main(string[] args)
  {

  Coffee sampleCoffee = new SimpleCoffee();
  Console.WriteLine("Cost: " + sampleCoffee.getCost() + " Ingredient: " + sampleCoffee.getIngredient());

        sampleCoffee = new Milk(sampleCoffee);
        Console.WriteLine("Cost: " + sampleCoffee.getCost() + " Ingredient: " + sampleCoffee.getIngredient());

        sampleCoffee = new Sprinkles(sampleCoffee);
        Console.WriteLine("Cost: " + sampleCoffee.getCost() + " Ingredient: " + sampleCoffee.getIngredient());

        sampleCoffee = new Whip(sampleCoffee);
        Console.WriteLine("Cost: " + sampleCoffee.getCost() + " Ingredient: " + sampleCoffee.getIngredient());

   Console.ReadKey();

  }
 }



//The Coffee Interface defines the functionality of Coffee implemented by decorator
public interface Coffee
{

    double getCost(); // returns the cost of coffee

    String getIngredient(); //returns the ingredients mixed with coffee
}

//implementation of simple coffee without any extra ingredients
public class SimpleCoffee : Coffee
{

    double cost;
    String ingredient;

    public SimpleCoffee()
    {
        cost = 1;
        ingredient = "Coffee";
    }

    public double getCost()
    {
        return cost;
    }

    public String getIngredient()
    {
        return ingredient;
    }
}



//abstract decorator class - note that it implements coffee interface
abstract public class CoffeeDecorator : Coffee
{

    protected Coffee decoratedCoffee;
    protected String ingredientSeparator;

    public CoffeeDecorator(Coffee decoratedCoffee)
    {
        this.decoratedCoffee = decoratedCoffee;
        ingredientSeparator = ", ";
    }

 public CoffeeDecorator()
 {

 }

    public double getCost() //note it implements the getCost function defined in interface Coffee
    {
        return decoratedCoffee.getCost();
    }

    public String getIngredient()
    {
        return decoratedCoffee.getIngredient();
    }
}

//Decorator Milk that mixes milk with coffee
//note it extends CoffeeDecorator
public class Milk : CoffeeDecorator
{

    double cost;
    String ingredient;

    public Milk(Coffee decoratedCoffee) : base(decoratedCoffee)
    {
        cost = 0.5;
        ingredient = "Milk";
    }

    public double getCost()
    {
        return base.getCost() + cost;
    }

    public String getIngredient()
    {
        return base.getIngredient() + base.ingredientSeparator + ingredient;
    }
}

//Decorator Whip that mixes whip with coffee
//note it extends CoffeeDecorator
public class Whip : CoffeeDecorator
{

    double cost;
    String ingredient;

 public Whip(Coffee decoratedCoffee)
  : base(decoratedCoffee)
    {
        cost = 0.7;
        ingredient = "Whip";
    }

    public double getCost()
    {
        return base.getCost() + cost;
    }

    public String getIngredient()
    {
        return base.getIngredient() + base.ingredientSeparator + ingredient;
    }
}

//Decorator Sprinkles that mixes sprinkles with coffee
//note it extends CoffeeDecorator
public class Sprinkles : CoffeeDecorator
{

    double cost;
    String ingredient;

    public Sprinkles(Coffee decoratedCoffee) : base(decoratedCoffee)
    {

        cost = 0.2;
        ingredient = "Sprinkles";
    }

    public double getCost()
    {
  return base.getCost() + cost;
    }

    public String getIngredient()
    {
  return base.getIngredient() + base.ingredientSeparator + ingredient;
    }
}

}

Answer 1

是 - 默认情况下,方法在Java中是虚拟的,但在C#中则不是.

在编译代码时,你应该收到警告,谈论"新"修饰符.那应该给你一个线索.目前你的Milk(等)方法正在隐藏或遮蔽那些CoffeeDecorator- 它们不是多态的.

您需要CoffeeDecorator使用virtual修饰符使方法成为虚拟,然后使用修饰符在Milk(等)中显式覆盖它们override.

// In CoffeeDecorator
public virtual double getCost()
{
    return decoratedCoffee.getCost();
}

// In Milk
public override double getCost()
{
    return base.getCost() + cost;
}