《設(shè)計模式筆記》之04建造者解析
建造者模式（Builder Pattern）使用多個簡單的對象一步一步構(gòu)建成一個復(fù)雜的對象。這種類型的設(shè)計模式屬于創(chuàng)建型模式，它提供了一種創(chuàng)建對象的最佳方式。
參考了菜鳥教程：https://www.runoob.com/design-pattern/builder-pattern.html
介紹
意圖：將一個復(fù)雜的構(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。
主要解決：主要解決在軟件系統(tǒng)中，有時候面臨著"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的算法構(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，但是將它們組合在一起的算法卻相對穩(wěn)定。
何時使用：一些基本部件不會變，而其組合經(jīng)常變化的時候。
如何解決：將變與不變分離開。
關(guān)鍵代碼：建造者：創(chuàng)建和提供實例，導(dǎo)演：管理建造出來的實例的依賴關(guān)系。
應(yīng)用實例： 1、去肯德基，漢堡、可樂、薯條、炸雞翅等是不變的，而其組合是經(jīng)常變化的，生成出所謂的"套餐"。 2、JAVA 中的 StringBuilder。
優(yōu)點： 1、建造者獨立，易擴展。 2、便于控制細節(jié)風險。
缺點： 1、產(chǎn)品必須有共同點，范圍有限制。 2、如內(nèi)部變化復(fù)雜，會有很多的建造類。
使用場景： 1、需要生成的對象具有復(fù)雜的內(nèi)部結(jié)構(gòu)。 2、需要生成的對象內(nèi)部屬性本身相互依賴。
注意事項：與工廠模式的區(qū)別是：建造者模式更加關(guān)注與零件裝配的順序。
UML圖
實現(xiàn)
Item 類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n62" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public interface Item {
//名稱
String name();
//包裝
Packing packing();
//價格
float price();
}</pre>
Packing及其實現(xiàn)類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n71" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public interface Packing {
String pack();
}
?
public class Bottle implements Packing {
@Override
public String pack() {
return "Bottle";
}
}
?
public class Wrapper implements Packing {
@Override
public String pack() {
return "Wrapper";
}
}</pre>
Burger類 及其實現(xiàn)類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n93" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public abstract class Burger implements Item {
@Override
public Packing packing() {
return new Wrapper();
}
}
?
public class ChickenBurger extends Burger {
@Override
public String name() {
return "ChickenBurger";
}
@Override
public float price() {
return 50.5f;
}
}
?
public class VegBurger extends Burger {
@Override
public String name() {
return "Veg Burger";
}
?
@Override
public float price() {
return 25.0f;
}
}</pre>
ColdDrink類及其實現(xiàn)類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n98" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public abstract class ColdDrink implements Item {
@Override
public Packing packing() {
return new Bottle();
}
}
?
public class Coke extends ColdDrink {
@Override
public String name() {
return "Coke";
}
@Override
public float price() {
return 10.5f;
}
}
?
public class Pepsi extends ColdDrink {
@Override
public String name() {
return "Pepsi";
}
?
@Override
public float price() {
return 11.5f;
}
}</pre>
Meal類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n103" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public class Meal {
private List<Item> items = new ArrayList<>();
?
public void addItem(Item item) {
items.add(item);
}
?
public float getCost() {
float cost = 0.0f;
for (Item item : items) {
cost += item.price();
}
return cost;
}
?
public void showItems() {
for (Item item : items) {
System.out.print("Item : " + item.name());
System.out.print(", Packing : " + item.packing().pack());
System.out.println(", Price : " + item.price());
}
}
}</pre>
MealBuilder類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n114" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public class MealBuilder {
?
public Meal prepareVegMeal() {
Meal meal = new Meal();
meal.addItem(new VegBurger());
meal.addItem(new Coke());
return meal;
}
?
public Meal prepareNonVegMeal() {
Meal meal = new Meal();
meal.addItem(new ChickenBurger());
meal.addItem(new Pepsi());
return meal;
}
}</pre>
運行類
<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" cid="n118" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-size: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; caret-color: rgb(51, 51, 51); color: rgb(51, 51, 51); font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; text-decoration: none; background-position: inherit inherit; background-repeat: inherit inherit;">public class BuilderPatternDemo {
?
public static void main(String[] args) {
MealBuilder mealBuilder = new MealBuilder();
?
Meal vegMeal = mealBuilder.prepareVegMeal();
System.out.println("Veg Meal");
vegMeal.showItems();
System.out.println("Total Cost: " + vegMeal.getCost());
?
Meal nonVegMeal = mealBuilder.prepareNonVegMeal();
System.out.println("Non-Veg Meal");
nonVegMeal.showItems();
System.out.println("Total Cost: " + nonVegMeal.getCost());
}
}</pre>
和工廠模式的區(qū)別
工廠模式主要工作是創(chuàng)建零件。
建造者模式主要工作是對創(chuàng)建的零件進行組裝。
