Builder模式的緣起：
??? 假設(shè)創(chuàng)建游戲中的一個房屋House設(shè)施，該房屋的構(gòu)建由幾部分組成，且各個部分富于變化。如果使用最直觀的設(shè)計方法，每一個房屋部分的變化，都將導(dǎo)致房屋構(gòu)建的重新修正.....
動機（Motivation):
??? 在軟件系統(tǒng)中，有時候面臨一個"復(fù)雜對象"的創(chuàng)建工作，其通常由各個部分的子對象用一定算法構(gòu)成;由于需求的變化，這個復(fù)雜對象的各個部分經(jīng)常面臨著劇烈的變化，但是將它們組合到一起的算法卻相對穩(wěn)定。
??? 如何應(yīng)對種變化呢？如何提供一種"封裝機制"來隔離出"復(fù)雜對象的各個部分"的變化，從而保持系統(tǒng)中的"穩(wěn)定構(gòu)建算法"不隨需求的改變而改變？
意圖(Intent)：
??? 將一個復(fù)雜對象的構(gòu)建與其表示相分離，使得同樣的構(gòu)建過程可以創(chuàng)建不同的表示。
??? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? -------《設(shè)計模式》GOF

結(jié)構(gòu)圖(Struct):????
???????????????

協(xié)作(Collaborations):
??????????????????

生活中的例子：
?????????????
適用性：
????1.當(dāng)創(chuàng)建復(fù)雜對象的算法應(yīng)該獨立于該對象的組成部分以及它們的裝配方式時。
??? 2.當(dāng)構(gòu)造過程必須允許被構(gòu)造的對象有不同的表示時。
實例代碼：
Builder類：

?1??public?abstract?class?Builder
?2?????{
?3?????????public?abstract?void?BuildDoor();
?4?????????public?abstract?void?BuildWall();
?5?????????public?abstract?void?BuildWindows();
?6?????????public?abstract?void?BuildFloor();
?7?????????public?abstract?void?BuildHouseCeiling();
?8?????
?9?????????public?abstract?House?GetHouse();
10?????}

Director類：這一部分是?組合到一起的算法（相對穩(wěn)定）。

1?public?class?Director
?2?????{
?3???????public?void?Construct(Builder?builder)
?4???????{
?5???????????builder.BuildWall();
?6???????????builder.BuildHouseCeiling();??????????
?7???????????builder.BuildDoor();
?8???????????builder.BuildWindows();
?9???????????builder.BuildFloor();?????????
10???????}
11?????}

ChineseBuilder類

?1????public?class?ChineseBuilder:Builder
?2?????{
?3????????private?House?ChineseHouse?=?new?House();
?4?????????public?override?void?BuildDoor()
?5?????????{
?6?????????????Console.WriteLine("this?Door?'s?style?of?Chinese");
?7?????????}
?8?????????public?override?void?BuildWall()
?9?????????{
10?????????????Console.WriteLine("this?Wall?'s?style?of?Chinese");
11?????????}
12?????????public?override?void?BuildWindows()
13?????????{
14?????????????Console.WriteLine("this?Windows?'s?style?of?Chinese");
15?????????}
16?????????public?override?void?BuildFloor()
17?????????{
18?????????????Console.WriteLine("this?Floor?'s?style?of?Chinese");
19?????????}
20?????????public?override?void?BuildHouseCeiling()
21?????????{
22?????????????Console.WriteLine("this?Ceiling?'s?style?of?Chinese");
23?????????}
24?????????public?override?House?GetHouse()
25?????????{
26?????????????return?ChineseHouse;
27?????????}
28?????}

RomanBuilder類：

?1?????class?RomanBuilder:Builder
?2?????{
?3?????????private?House?RomanHouse?=?new?House();
?4?????????public?override?void?BuildDoor()
?5?????????{
?6?????????????Console.WriteLine("this?Door?'s?style?of?Roman");
?7?????????}
?8?????????public?override?void?BuildWall()
?9?????????{
10?????????????Console.WriteLine("this?Wall?'s?style?of?Roman");
11?????????}
12?????????public?override?void?BuildWindows()
13?????????{
14?????????????Console.WriteLine("this?Windows?'s?style?of?Roman");
15?????????}
16?????????public?override?void?BuildFloor()
17?????????{
18?????????????Console.WriteLine("this?Floor?'s?style?of?Roman");
19?????????}
20?????????public?override?void?BuildHouseCeiling()
21?????????{
22?????????????Console.WriteLine("this?Ceiling?'s?style?of?Roman");
23?????????}
24?????????public?override?House?GetHouse()
25?????????{
26?????????????return?RomanHouse;
27?????????}
28?????}

ChineseBuilder和RomanBuilder這兩個是：這個復(fù)雜對象的兩個部分經(jīng)常面臨著劇烈的變化。

?1???public?class?Client
?2?????{
?3?????????public?static?void?Main(string[]?args)
?4?????????{
?5?????????????Director?director?=?new?Director();
?6?
?7?????????????Builder?instance;
?8?
?9?????????????Console.WriteLine("Please?Enter?House?No:");
10?
11?????????????string?No?=?Console.ReadLine();
12?
13?????????????string?houseType?=?ConfigurationSettings.AppSettings["No"?+?No];
14?
15?????????????instance?=?(Builder)Assembly.Load("House").CreateInstance("House."?+?houseType);
16?
17?????????????director.Construct(instance);
18?
19?????????????House?house=?instance.GetHouse();
20?????????????house.Show();
21?
22?????????????Console.ReadLine();
23?????????}
24?????}

?

1?<?xml?version="1.0"?encoding="utf-8"??>
2?<configuration>
3???<appSettings>
4?????<add?key="No1"?value="RomanBuilder"></add>
5?????<add?key="No2"?value="ChineseBuilder"></add>
6???</appSettings>
7?</configuration>


Builder模式的幾個要點:

Builder模式 主要用于“分步驟構(gòu)建一個復(fù)雜的對象”。在這其中“分步驟”是一個穩(wěn)定的乘法，而復(fù)雜對象的各個部分則經(jīng)常變化。

Builder模式主要在于應(yīng)對“復(fù)雜對象各個部分”的頻繁需求變動。其缺點在于難以應(yīng)對“分步驟構(gòu)建算法”的需求變動。

Abstract Factory模式解決“系列對象”的需求變化，Builder模式解決“對象部分”的需求變化。Builder械通常和Composite模式組合使用。

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