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当我在中产阶级中使用抽象关键字时,代码不起作用

abstract-class design-patterns c#

Dr. Rajesh Rolen · 技术社区 · 16 年前

我有下面的代码,运行良好:

  public abstract class Beverage
{
    public string description = "Unknown beverage";
    public virtual  string getDescription()
    {
        return description;
    }
    public abstract double cost();
}

public abstract class condimentDecorator : Beverage
{
   // public abstract string getDescription();
}

public class DarkRoast : Beverage
{
    public DarkRoast()
    {
        description = "DarkRoast";
    }
    public override  double cost()
    {
        return 2.10;
    }
}
public class Espresso : Beverage
{
    public Espresso()
    {
        description = "Espresso";
    }
    public override double cost()
    {
        return 1.99;
    }
}

public class HouseBlend : Beverage
{
    public HouseBlend()
    {
        description = "House Blend Coffee";
    }
    public override double cost()
    {
        return .89;
    }
}


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 .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 .10 + 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 .10 + beverage.cost();
    }
}

我使用它的方式是:

 protected void Page_Load(object sender, EventArgs e)
    {
        Beverage beverage2 = new DarkRoast();
        beverage2 = new Mocha(beverage2);
        beverage2 = new Mocha(beverage2);
        beverage2 = new Whip(beverage2);
        Response.Write ("<br> " + beverage2.getDescription() + " : $" + beverage2.cost().ToString());
    }

问题:我希望“conditionmentdecorator”的所有子类都强制重写getdescription()function,因为我已经在“conditionmentdecorator”类中编写了以下代码:

 public abstract string getDescription();

但这改变了我当前的功能,并没有给出期望的结果,它只显示了“未知饮料”作为getDescription()的值,而getDescription()是大多数父类的值。

正常结果:

DarkRoast, Mocha, Mocha, Whip : $2.6

使用“public abstract string getdescription()”后的结果:

Unknown beverage : $2.6

请建议我应该编写/更改什么,这样我就可以强制“conditionmentDecorator”的子类重写“getDescription();”,并在没有它的情况下得到resutl。

3 回复 | 直到 16 年前

Isak Savo 16 年前

我认为你的阶级结构需要重新思考。

这个怎么样:

我建议您创建一个接口, IBeverage 你在所有可饮用的东西上都能实现。然后你为“基本”饮料创造了一个基础类——黑烤肉、浓缩咖啡、室内混合饮料——就像你现在做的那样。

对于调味品,可以实现实现IBeverage的新抽象基类,但不提供默认值 GetDescription 实施。这个类还可以在其构造函数中使用IBeverage来强制其他调味品执行相同的操作。

我认为这样的方法应该有效(未经测试,未编译-但你知道这个主意)

public interface IBeverage
{
  string GetDescription ();
}

public abstract class BeverageBase : IBeverage
{
  public virtual string GetDescription () { return "Unknown Beverage"; }
}

public class DarkRoast : BeverageBase { ... }
public class HouseBlend : BeverageBase { ...}

public abstract class CondimentBase : IBeverage
{
  public CondimentBase(IBeverage beverage)
  {
    Beverage = beverage;
  }
  protected IBeverage Beverage { get; set; }
  public abstract string GetDescription ();
}

public class Mocha : CondimentBase 
{
  public Mocha(IBeverage beverage)
    : base (beverage)
  { }
  public string GetDescription()
  {
    return Beverage.GetDescription() + ", Mocha";
  }
}

Euphoric 16 年前

快速谷歌发现了这一点: http://codebetter.com/blogs/darrell.norton/archive/2005/05/18/63332.aspx

我没有尝试代码本身。

testalino 16 年前

您可以创建这样的新方法:

public abstract class condimentDecorator : Beverage
{
     public override string getDescription()
     {
          return getDescriptionInternal();
     }
     protected abstract string getDescriptionInternal();
}

这样,所有类都必须间接实现getdescription。