工厂方法-Factory method

这应该是大家学design pattern第一个遇到的pattern吧，这个pattern有两个角色

简单说就是透过Factory来生产Product，client只需要告诉Factory，我要一个什么Product，然后就得到他要的Product了。

架构图长这样：

範例

我现在要去吃pizza了，所以需要定义：

当然都要是AbstractClass 或 interface，不应该把实作内容直接写在这边，物件导向语言的其中一个守则：针对介面写程式，不是针对实践方法写程式

宣告Factory

public abstract class PizzaStore {    public abstract Pizza createPizza(String type);     public Pizza orderPizza(String type) { // client只要呼叫这个method就好        Pizza pizza = createPizza(type);        pizza.prepare();        pizza.bake();        pizza.cut();        pizza.box();        return pizza;    }}

宣告Product

package com.example.designpattern.creational.factory_method.example2;public abstract class Pizza {    String name;    String dough;    String sauce;    // method都不是宣告为abstract，如果subClass不用客製，就不用override    void prepare() {        System.out.println("Preparing: " + name + ", " + dough + ", " + sauce );        System.out.println("Tossing dough...");    };        void bake() {        System.out.println("Bake for 25 minutes at 350");    }        void cut() {        System.out.println("Cutting pizza into diagonal slices");    }        void box() {        System.out.println("Place pizza in official PizzaStore box");    }}

有了Factory跟Product后，就可以继承他们来写concreteClass了
先写Factory，NYPizzaStore

package com.example.designpattern.creational.factory_method.example2;public class NYPizzaStore extends PizzaStore {    @Override    public Pizza createPizza(String type) {        Pizza pizza = null;                // 这间PizzaStore可以生产两种Pizza        if("cheese".equals(type)) {            pizza = new NYCheesePizza();        } else if ("sausage".equals(type)) {            pizza = new NYSausagePizza();        }        return pizza;    }    @Override    public Pizza orderPizza(String type) {        return super.orderPizza(type);    }}

再来是Product，第一种Product NYCheesePizza

package com.example.designpattern.creational.factory_method.example2;public class NYCheesePizza extends Pizza {    String name = "NYCheesePizza";    String dough = "crispy";    String sauce = "cheese sauce";    @Override    void prepare() {        System.out.println("Amazing~~~ " + name +" , " + dough + " , " + sauce);    }        @Override    void bake() {        System.out.println("Bake for 15 minutes at 400");    }        @Override    void cut() {        System.out.println("Cutting pizza into 8 slices");    }}

第二种Prodcut NYSausaePizze

package com.example.designpattern.creational.factory_method.example2;public class NYSausagePizza extends Pizza {   String name = "NY Sausage pizze";   String dough = "Thick";   String sauce = "Marinara sauce";    @Override    void prepare() {        System.out.println(name +" , " + dough + " , " + sauce);    }}

Client 要来点pizza了

package com.example.designpattern.creational.factory_method.example2;public class PizzaClient {    public static void main(String[] args) {        // 进入NYPizzaStore        PizzaStore pizzaStore = new NYPizzaStore();                // 我要cheese pizza，啪，cheesePizza        Pizza cheesePizza = pizzaStore.orderPizza("cheese");        System.out.println("---------------");                // 我要sausage pizza，啪，sausagePizza        Pizza sausagePizza = pizzaStore.orderPizza("sausage");     }    /*        output:        Amazing~~~ NYCheesePizza , crispy , cheese sauce        Bake for 15 minutes at 400        Cutting pizza into 8 slices        Place pizza in official PizzaStore box                ---------------        NY Sausage pizze , Thick , Marinara sauce        Bake for 25 minutes at 350        Cutting pizza into diagonal slices        Place pizza in official PizzaStore box     */}

Reference:

https://refactoring.guru/design-patterns/factory-method
https://www.oreilly.com/library/view/head-first-design/0596007124/