[讀書心得]深入淺出物件導向分析與設計-良好程式設計基石 OOAD Code設計範例介紹-3

2008-02-11

7487
0
C#

在上一篇最後提到的，3.達成可維護、可重利用的設計，這篇文章就介紹關於第三個範例，
如果要增加一個全新的屬性進來時，如何透過封裝的方式，讓程式碼的影響範圍減少。

在上一篇最後提到的，3.達成可維護、可重利用的設計，這篇文章就介紹關於第三個範例，

接下來我們面對一個新的問題，如果要增加一個全新的屬性進來時，我們的程式會面臨到多少的修改呢?
首先增加一個新的屬性吉他弦數那我們會影響到要修改的程式有多少呢? 程式詳細連結
1.GuitarSpec要增加一個屬性
2.Guutar 建構式增加這個屬性
3.Inventory 下 search() 的比對要增加
當要新增一個屬性進來的時候，就必須修改 GuitarSpec.cs Guutar.cs Inventory.cs程式碼，
而現在將修正這個牽連太多物件問題，
將透過封裝的方式，來讓程式的擴充性更高，
Step1.我們增加吉他弦數的特性到GuitarSpec.cs


{

    private Builder builder;
    private String model;
    private Type type;
    //增加弦數
    private int numStrings;
    private Wood backWood;
    private Wood topWood;
    //建構式這邊也增加對應
    public GuitarSpec(Builder builder, String model, Type type,
                      int numStrings, Wood backWood, Wood topWood)
    {
        this.builder = builder;
        this.model = model;
        this.type = type;
        this.numStrings = numStrings;
        this.backWood = backWood;
        this.topWood = topWood;
    }

    public Builder getBuilder()
    {
        return builder;
    }

    public String getModel()
    {
        return model;
    }

    public Type getType()
    {
        return type;
    }

    public int getNumStrings()
    {
        return numStrings;
    }

    public Wood getBackWood()
    {
        return backWood;
    }

    public Wood getTopWood()
    {
        return topWood;
    }

    //原本Inventory的search的程式碼被抽到這裡
    public bool matches(GuitarSpec otherSpec)
    {
        if (builder != otherSpec.builder)
            return false;
        if ((model != null) && (!model.Equals("")) &&
            (!model.ToLower().Equals(otherSpec.model.ToLower())))
            return false;
        if (type != otherSpec.type)
            return false;
        if (numStrings != otherSpec.numStrings)
            return false;
        if (backWood != otherSpec.backWood)
            return false;
        if (topWood != otherSpec.topWood)
            return false;
        return true;
    }
}


Step2.將Guitar.cs 建構式改為傳入GuitarSpec

public class Guitar
{

    private String serialNumber;
    private double price;

    GuitarSpec spec;
    //改為直接接受一個GuitarSpec
    public Guitar(String serialNumber, double price, GuitarSpec spec)
    {
        this.serialNumber = serialNumber;
        this.price = price;
        this.spec = spec;
    }

    public String getSerialNumber()
    {
        return serialNumber;
    }

    public double getPrice()
    {
        return price;
    }

    public void setPrice(float newPrice)
    {
        this.price = newPrice;
    }

    public GuitarSpec getSpec()
    {
        return spec;
    }
}


Step3.改變Invetory.cs 的search 將比較的程式抽至 GuitarSpec

public class Inventory
{
  
    private List<Guitar> guitars;

    public Inventory()
    {
        guitars = new List<Guitar>();
    }

    public void addGuitar(String serialNumber, double price,
                         GuitarSpec spec)
    {
        Guitar guitar = new Guitar(serialNumber, price, spec);
        guitars.Add(guitar);
    }
    public Guitar getGuitar(String serialNumber)
    {
        foreach(Guitar guitar in guitars)       
        {
            
            if (guitar.getSerialNumber().Equals(serialNumber))
            {
                return guitar;
            }
        }
        return null;
    }
    //讓search變的比較單純
    public List<Guitar> search(GuitarSpec searchSpec)
    {
        List<Guitar> matchingGuitars = new List<Guitar>();

        foreach (Guitar guitar in guitars)       
        {
            GuitarSpec guitarSpec = guitar.getSpec();
            //將兩個GuitarSpec委派給GuitarSpec類別來做比較而不是把比較邏輯寫在Inventory的search裡面
            if (guitar.getSpec().matches(searchSpec))
                matchingGuitars.Add(guitar);
           
        }
        //既使比對條件改變但回傳還是回傳Guitar清單
        return matchingGuitars;
    }
}


Step4.測試程式，將本來的建構式做修改default.aspx.cs


 Inventory inventory = new Inventory();
        //給予Inventory數據
        initializeInventory(inventory);


  //新增了弦數的建構式
        GuitarSpec whatErinLikes =  new GuitarSpec(Builder.FENDER, "Stratocastor",
                   Type.ELECTRIC, 6, Wood.ALDER, Wood.ALDER);

        //這一次是傳入GuitarSpec給Search
            List<Guitar> matchingGuitars = inventory.search(whatErinLikes);

          if (matchingGuitars.Count > 0)
          {
              Response.Write("Erin, you might like these guitars:</BR> ");
                foreach (Guitar guitar in matchingGuitars)
                {
                    //取的該Guitar下的GuitarSpec
                    GuitarSpec spec = guitar.getSpec();
                    Response.Write("  We have a " +
                    spec.getBuilder() + " " + spec.getModel() + " " +
                    spec.getType() + " guitar:</BR>     " +
                    spec.getBackWood() + " back and sides,</BR>      " +
                    spec.getTopWood() + " top.</BR>  You can have it for only $" +
                    guitar.getPrice() + "!</BR>   " + guitar.getSerialNumber() + "----");
                }
            }
          else 
          {
              Response.Write("Sorry, Erin, we have nothing for you.");
          }


// 上面這段是 Page_Load
// 下面是新的 initializeInventory 傳入GuitarSpec


   private static void initializeInventory(Inventory inventory)
    {
        inventory.addGuitar("11277", 3999.95,
          new GuitarSpec(Builder.COLLINGS, "CJ", Type.ACOUSTIC, 6,
                         Wood.INDIAN_ROSEWOOD, Wood.SITKA));
        inventory.addGuitar("V95693", 1499.95,
          new GuitarSpec(Builder.FENDER, "Stratocastor", Type.ELECTRIC, 6,
                         Wood.ALDER, Wood.ALDER));
        inventory.addGuitar("V9512", 1549.95,
          new GuitarSpec(Builder.FENDER, "Stratocastor", Type.ELECTRIC, 6,
                         Wood.ALDER, Wood.ALDER));
        inventory.addGuitar("122784", 5495.95,
          new GuitarSpec(Builder.MARTIN, "D-18", Type.ACOUSTIC, 6,
                         Wood.MAHOGANY, Wood.ADIRONDACK));
        inventory.addGuitar("76531", 6295.95,
          new GuitarSpec(Builder.MARTIN, "OM-28", Type.ACOUSTIC, 6,
                         Wood.BRAZILIAN_ROSEWOOD, Wood.ADIRONDACK));
        inventory.addGuitar("70108276", 2295.95,
          new GuitarSpec(Builder.GIBSON, "Les Paul", Type.ELECTRIC, 6,
                         Wood.MAHOGANY, Wood.MAHOGANY));
        inventory.addGuitar("82765501", 1890.95,
          new GuitarSpec(Builder.GIBSON, "SG '61 Reissue", Type.ELECTRIC, 6,
                         Wood.MAHOGANY, Wood.MAHOGANY));
        inventory.addGuitar("77023", 6275.95,
          new GuitarSpec(Builder.MARTIN, "D-28", Type.ACOUSTIC, 6,
                         Wood.BRAZILIAN_ROSEWOOD, Wood.ADIRONDACK));
        inventory.addGuitar("1092", 12995.95,
          new GuitarSpec(Builder.OLSON, "SJ", Type.ACOUSTIC, 12,
                         Wood.INDIAN_ROSEWOOD, Wood.CEDAR));
        inventory.addGuitar("566-62", 8999.95,
          new GuitarSpec(Builder.RYAN, "Cathedral", Type.ACOUSTIC, 12,
                         Wood.COCOBOLO, Wood.CEDAR));
        inventory.addGuitar("6 29584", 2100.95,
          new GuitarSpec(Builder.PRS, "Dave Navarro Signature", Type.ELECTRIC,
                         6, Wood.MAHOGANY, Wood.MAPLE));
    }


四個步驟完成後，首先你會發現，我們讓Invetory.cs 下的search 變的簡單，讓實際比較的邏輯移到了
GuitarSpec 裡面的 matches 裡。
而當我們如果又遇到要再增加一個顏色屬性的時候，我們只需更動 GuitarSpec.cs 的建構式及matches
而以不在像是之前的程式需同時牽動到 Guitar.cs , Inventory.cs


{

    private Builder builder;
    private String model;
    private Type type;
    //增加弦數
    private int numStrings;
    private Wood backWood;
    private Wood topWood;

    //增加顏色
    private string color;
    //建構式這邊也增加對應
    public GuitarSpec(Builder builder, String model, Type type,
                      int numStrings, Wood backWood, Wood topWood,string color)
    {
        this.builder = builder;
        this.model = model;
        this.type = type;
        this.numStrings = numStrings;
        this.backWood = backWood;
        this.topWood = topWood;
        this.color = color;
    }

    public string getColir()
    {
        return color;
    }

    public Builder getBuilder()
    {
        return builder;
    }

    public String getModel()
    {
        return model;
    }

    public Type getType()
    {
        return type;
    }

    public int getNumStrings()
    {
        return numStrings;
    }

    public Wood getBackWood()
    {
        return backWood;
    }

    public Wood getTopWood()
    {
        return topWood;
    }

    //原本Inventory的search的程式碼被抽到這裡
    public bool matches(GuitarSpec otherSpec)
    {
        if (builder != otherSpec.builder)
            return false;
        if ((model != null) && (!model.Equals("")) &&
            (!model.ToLower().Equals(otherSpec.model.ToLower())))
            return false;
        if (type != otherSpec.type)
            return false;
        if (numStrings != otherSpec.numStrings)
            return false;
        if (backWood != otherSpec.backWood)
            return false;
        if (topWood != otherSpec.topWood)
            return false;
        //增加Color的比對
        if ((color != null) && (!color.Equals("")) &&
           (!color.ToLower().Equals(otherSpec.color.ToLower())))
            return false;
        return true;
    }
}


而測試頁面在建構GuitarSpec時多增加一個屬性，其他本來的程式都沒有任何的修改，
則還是能繼續的運作。


 //新增了顏色
        GuitarSpec whatErinLikes = new GuitarSpec(Builder.FENDER, "Stratocastor",
                 Type.ELECTRIC, 6, Wood.ALDER, Wood.ALDER,"Red");

        //這一次是傳入GuitarSpec給Search
            List<Guitar> matchingGuitars = inventory.search(whatErinLikes);


透過這三個程式的演進，慢慢的可以感覺出來透過「物件」方式的設計的感覺是什麼，
如同第一篇文章提到書中所寫到的
好的軟體的三個步驟 
1.確認客戶要做的事情。 
2.應用基本的OO原則，增加軟體彈性。 
3.努力達成可維護、重利用的設計。

透過三個範例程式，一步一步的演進，讓Dotjum第一次有悟道要如何做一個物件化的程式，

書中還提到許多觀念及說明，Dotjum無法一個一個的打上來，但針對程式的演進的部分，
就做了一個詳細的說明，這真的是一本不錯的書，若之後章節Dotjum也能夠悟道，
在Po上來跟大家分享。若你覺得文章有什麼你的想法或建議，在麻煩你回覆，我們一起來討論。
本範例的.NET Code HeadFirstOOAD.rar




本篇文章程式碼及概念取用 深入淺出物件導向分析與設計 
(若觀念等相關錯誤有錯誤，請務必告訴Dotjum)

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[讀書心得]深入淺出物件導向分析與設計-良好程式設計基石 OOAD Code設計範例介紹-1

[讀書心得]深入淺出物件導向分析與設計-良好程式設計基石 OOAD Code設計範例介紹-2

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