建造者模式 (Builder Pattern)

October 12, 2023

Design Pattern

本文介紹設計模式中的建造者模式，並使用 C# 撰寫範例。

主要的類別

  1. Builder Interface: 定義須實做的方法。
  2. 實際的 Builder Class: 呼叫基礎的 Product 類別，並實作個別的差異性。
  3. Product Class: 基礎類別。
  4. Director Class: 組合 Builder 的建造步驟 (非必要)。

要解決的問題

  1. 建構子太長的問題。
  2. 不需要參數時，需填入 null 的情形。
  3. 避免有很多類似的建構子。

注意

  1. 基礎的方法相同時，比較適用此模式。
  2. 可能會產生很多的 Builder 類別。

範例程式碼

Builder.cs

public interface IHouseBuilder{
    IHouseBuilder SetBathroom();
    IHouseBuilder SetLivingRoom();
    IHouseBuilder SetBedroom(int n);
    IHouseBuilder SetKitchen();
    IHouseBuilder SetDiningRoom();
    IHouseBuilder SetBalcony();
    House Build();
}

public class House{
    private string title;
    private List<string> listDesc;

    public House(string title){
        this.title = title;
        listDesc = new List<string>();
    }
    
    public void Show(){
        Console.WriteLine($"**{title}**");
        foreach(string desc in listDesc){
            Console.WriteLine($"- {desc}");
        }
    }

    public void SetBathroom(){
        listDesc.Add("建造 1 個浴廁");
    }

    public void SetLivingRoom(){
        listDesc.Add("建造 1 個客廳");
    }

    public void SetBedroom(int n){
        listDesc.Add($"建造 {n} 個臥室");
    }

    public void SetKitchen(){
        listDesc.Add("建造 1 個廚房");
    }

    public void SetDiningRoom(){
        listDesc.Add("建造 1 個餐廳");
    }

    public void SetBalcony(){
        listDesc.Add("建造 1 個陽台");
    }
}

public class EuropeHouseBuilder: IHouseBuilder{
    private House _house;

    public EuropeHouseBuilder(){
        _house = new House("歐風洋房");
    }

    public IHouseBuilder SetBathroom(){
        _house.SetBathroom();
        return this;
    }

    public IHouseBuilder SetLivingRoom(){
        _house.SetLivingRoom();
        return this;
    }

    public IHouseBuilder SetBedroom(int n){
        _house.SetBedroom(n);
        return this;
    }

    public IHouseBuilder SetKitchen(){
        _house.SetKitchen();
        return this;
    }

    public IHouseBuilder SetDiningRoom(){
        _house.SetDiningRoom();
        return this;
    }

    public IHouseBuilder SetBalcony(){
        _house.SetBalcony();
        return this;
    }

    public House Build(){
        return _house;
    }
}

public class JapaneseHouseBuilder: IHouseBuilder{
    private House _house;

    public JapaneseHouseBuilder(){
        _house = new House("日式木屋");
    }

    public IHouseBuilder SetBathroom(){
        _house.SetBathroom();
        return this;
    }

    public IHouseBuilder SetLivingRoom(){
        _house.SetLivingRoom();
        return this;
    }

    public IHouseBuilder SetBedroom(int n){
        _house.SetBedroom(n);
        return this;
    }

    public IHouseBuilder SetKitchen(){
        _house.SetKitchen();
        return this;
    }

    public IHouseBuilder SetDiningRoom(){
        _house.SetDiningRoom();
        return this;
    }

    public IHouseBuilder SetBalcony(){
        _house.SetBalcony();
        return this;
    }

    public House Build(){
        return _house;
    }
}

Director

public class Director{
    IHouseBuilder builder;

    public Director(IHouseBuilder builder){
        this.builder = builder;
    }

    public House BuildLuxuryHouse(){
        return builder.SetBalcony()
                    .SetBathroom()
                    .SetBedroom(4)
                    .SetDiningRoom()
                    .SetKitchen()
                    .SetLivingRoom()
                    .Build();
    }

    public House BuildBasicHouse(){
        return builder.SetBathroom()
                    .SetBedroom(2)
                    .SetDiningRoom()
                    .SetKitchen()
                    .Build();
    }
}

Main.cs

House myEuropeHouse = new EuropeHouseBuilder()
                        .SetBalcony()
                        .SetBedroom(1)
                        .SetBathroom()
                        .SetLivingRoom()
                        .SetKitchen()
                        .Build();

House myJapaneseHouse = new JapaneseHouseBuilder()
                        .SetBalcony()
                        .SetBedroom(2)
                        .SetBathroom()
                        .SetDiningRoom()
                        .SetKitchen()
                        .Build();

Director europeHouseDirector = new Director(new EuropeHouseBuilder());
House luxuryEuropeHouse = europeHouseDirector.BuildLuxuryHouse();

Director japaneseHouseDirector = new Director(new JapaneseHouseBuilder());
House basicJapaneseHouse = japaneseHouseDirector.BuildBasicHouse();

myEuropeHouse.Show();
myJapaneseHouse.Show();
luxuryEuropeHouse.Show();
basicJapaneseHouse.Show();

參考資料