177 lines
3.3 KiB
Dart
177 lines
3.3 KiB
Dart
/**
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建造者模式（Builder Pattern）
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意图：将一个复杂的构建与其表示相分离，使得同样的构建过程可以创建不同的表示。
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主要解决：主要解决在软件系统中，有时候面临着"一个复杂对象"的创建工作，其通常由各个部分的子对象用一定的算法构成；由于需求的变化，这个复杂对象的各个部分经常面临着剧烈的变化，但是将它们组合在一起的算法却相对稳定。
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何时使用：一些基本部件不会变，而其组合经常变化的时候。
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如何解决：将变与不变分离开。
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*/
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main(List<String> args) {
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MealBuilder mealBuilder = new MealBuilder();
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Meal vegMeal = mealBuilder.prepareVegMeal();
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print("Veg Meal");
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vegMeal.showItems();
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print("Total Cost: ${vegMeal.getCost()}");
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Meal nonVegMeal = mealBuilder.prepareNonVegMeal();
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print("\n\nNon-Veg Meal");
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nonVegMeal.showItems();
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print("Total Cost: ${nonVegMeal.getCost()}");
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}
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//////////////////////////////////////////////////////////////////
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///
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/// 创建一个表示 食物条目 的接口
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///
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abstract class Item {
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String name();
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Packing packing();
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double price();
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}
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///
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/// 创建一个表示 食物包装 的接口
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///
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abstract class Packing {
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String pack();
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}
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///
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/// 创建实现 Packing 接口的实体类
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///
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class Wrapper implements Packing {
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@override
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String pack() {
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return "Wrapper";
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}
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}
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class Bottle implements Packing {
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@override
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String pack() {
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return "Bottle";
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}
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}
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///
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/// 创建实现 Item 接口的抽象类，该类提供了默认的功能
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///
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abstract class Burger implements Item {
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@override
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Packing packing() {
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return new Wrapper();
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}
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@override
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double price();
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}
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abstract class ColdDrink implements Item {
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@override
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Packing packing() {
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return new Bottle();
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}
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@override
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double price();
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}
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///
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/// 创建扩展了 Burger 和 ColdDrink 的实体类
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///
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class VegBurger extends Burger {
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@override
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double price() {
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return 25.0;
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}
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@override
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String name() {
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return "Veg Burger";
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}
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}
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class ChickenBurger extends Burger {
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@override
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double price() {
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return 50.5;
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}
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@override
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String name() {
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return "Chicken Burger";
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}
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}
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class Coke extends ColdDrink {
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@override
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double price() {
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return 30.0;
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}
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@override
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String name() {
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return "Coke";
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}
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}
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class Pepsi extends ColdDrink {
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@override
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double price() {
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return 35.0;
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}
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@override
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String name() {
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return "Pepsi";
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}
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}
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///
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/// 创建一个 Meal 类，带有上面定义的 Item 对象
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///
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class Meal {
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List<Item> _items = List<Item>();
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void addItem(Item item) {
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_items.add(item);
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}
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double getCost() {
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double cost = 0.0;
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for (Item item in _items) {
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cost += item.price();
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}
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return cost;
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}
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void showItems() {
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for (Item item in _items) {
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print("Item : ${item.name()}");
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print(", Packing : ${item.packing().pack()}");
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print(", Price : ${item.price()}");
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}
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}
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}
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///
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/// 创建一个 MealBuilder 类，实际的 builder 类负责创建 Meal 对象
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///
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class MealBuilder {
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Meal prepareVegMeal() {
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Meal meal = new Meal();
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meal.addItem(new VegBurger());
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meal.addItem(new Coke());
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return meal;
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}
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Meal prepareNonVegMeal() {
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Meal meal = new Meal();
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meal.addItem(new ChickenBurger());
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meal.addItem(new Pepsi());
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return meal;
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}
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}
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