为什么缺乏凝聚力的方法（LCOM）中包括getter和setter [英] Why Does Lack of Cohesion Of Methods (LCOM) Include Getters and Setters

问题描述

我在看的LCOM指标如下所示，

I am looking at the LCOM metric as shown here,

http://www.ndepend.com/Metrics.aspx

因此​​，我们说了一些东西，

So we are saying a few things,

1) A class is utterly cohesive if all its methods use all its instance fields
2) Both static and instance methods are counted, it includes also constructors, properties getters/setters, events add/remove methods

如果我看的一类，如此，

If I look at a class such as this,

public class Assessment
{
    public int StartMetres { get; set; }
    public int EndMetres { get; set; }
    public decimal? NumericResponse { get; set; }
    public string FreeResponse { get; set; }
    public string Responsetype { get; set; }
    public string ItemResponseDescription { get; set; }
    public string StartText { get; set; }
    public decimal? SummaryWeight { get; set; }
}

它得到一个坏的评分为0.94，因为每个getter和setter不访问​​所有其他实例字段的

It gets a bad score of 0.94 because each getter and setter doesn't access 'all of the other instance fields'.

据计算这个样子，

accessAverage - methodCount / 1 - methodCount

(2 - 17) / (1 - 17) = 0.94 (rounded)

我不理解这个指标，为什么要包括getter和setter方法​​？一个getter和setter将永远只能访问一个单一的实例字段。

I am not understanding this metric, why should it include getters and setters? A getter and setter will always only access one single instance field.

推荐答案

这表明，每个软件度量是有缺陷的，如果你一味地把它发挥到极致。

This demonstrates that every software metric is flawed if you blindly take it to its extreme.

您知道一个无凝聚力级，当你看到一个。例如：

You know an "incohesive" class when you see one. For example:

class HedgeHog_And_AfricanCountry
{

   private HedgeHog _hedgeHog;
   private Nation _africanNation;

   public ulong NumberOfQuills { get { return _hedgeHog.NumberOfQuills; } }
   public int CountOfAntsEatenToday { get { return _hedgeHog.AntsEatenToday.Count(); } }

   public decimal GrossDomesticProduct { get { return _africanNation.GDP; } }
   public ulong Population { get { return _africanNation.Population; } }
}

这显然是一个无凝聚力类，因为它包含两个数据不需要与彼此

This is obviously an incohesive class, because it contains two pieces of data that don't need to be with one another.

不过，虽然这是明显地向我们这个类是无凝聚力，你怎么能得到一个软件程序来确定incohesion？如何将它告诉大家，上面的类是无凝聚力，但这不是？

But while it's obvious to us that this class is incohesive, how can you get a software program to determine incohesion? How would it tell that the above class is incohesive, but this isn't?

class Customer
{
    public string FullName { get; set; }
    public Address PostalAddress { get; set; }
} 

他们想出了度量肯定检测incohesion，而且还附带了误报。

The metric they came up with certainly detects incohesion, but also comes up with false positives.

如果你确定这个指标是很重要的是什么？你可以创建一个CustomerData级只包含字段和公开的数据字段属性客户类。

What if you decided this metric was important? You could create a "CustomerData" class containing just fields, and a "Customer" class that exposes the data fields as properties.

// This has no methods or getters, so gets a good cohesion value.
class CustomerData
{
    public string FullName;
    public Address PostalAddress;
}

// All of the getters and methods are on the same object
class Customer
{
   private CustomerData _customerData;
   public string FullName { get { return _customerData.FullName; } }
   // etc
}

但是，如果我在玩这个游戏，我可以把它应用到无凝聚力的例子还有：

But if I'm playing this game, I can apply it to the incohesive example as well:

class Hedgehog_And_AfricanCountry_Data
{
   public Hedgehog _hedgehog;
   public AfricanNation _africanNation;
}

class Hedgehog_And_AfricanCountry
{
   private Hedgehog_And_AfricanCountry_Data _hedgehogAndAfricanCountryData;
   // etc;
}

说真的，我认为这是最好理解的凝聚力是什么，以及为什么它是一个值得追求的目标，但也明白，一个软件工具不能正确测量。

Really, I think it's best to understand what cohesion is, and why it's a worthwhile goal, but also understand that a software tool can not properly measure it.

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