描述

工廠模式用以封裝復雜的實例初始化過程，供外部統一調用

簡單工廠（靜態工廠）

如果對象創建邏輯簡單且一致，可以使用簡單工廠。傳入想要生成的實例類型

public class HumanFactory {public static <T> T getInstance(Class<T> c) {try {return (T) Class.forName(c.getName()).getDeclaredConstructor().newInstance();} catch (Exception e) {throw new RuntimeException("生成對象異常", e);}}
}

工廠方法模式

多種類型產品初始化邏輯不一致時，可以采用不同工廠實例來初始化對應類型的產品
由于每種產品定義了對應的工廠類，因此工廠方法不需要類型參數就非常明確需要創建的實例

• 聲明工廠抽象定義

public abstract class AbstractProductFactory {public abstract Product createProduct();
}

• 聲明產品抽象定義

public interface Product {String getName();default void description() {System.out.println("產品名稱：" + getName());}
}

• 定義具體產品

public class Apple implements Product {@Overridepublic String getName() {return "蘋果";}
}public class Banana implements Product {@Overridepublic String getName() {return "香蕉";}
}

• 定義產品對應的工廠

public class AppleFactory extends AbstractProductFactory {public Product createProduct() {// 蘋果其他初始化邏輯return new Apple();}
}public class BananaFactory extends AbstractProductFactory {public Product createProduct() {// 香蕉其他初始化邏輯return new Banana();}
}

• 使用

public static void main(String[] args) {AbstractProductFactory appleFactory = new AppleFactory();Product product = appleFactory.createProduct();product.description();AbstractProductFactory bananaFactory = new BananaFactory();Product banana = bananaFactory.createProduct();banana.description();
}

抽象工廠

以上工廠方法，一個產品就需要一個工廠類。
如果產品本身就有一些共通的地方，我們可以將產品劃分到同一個工廠的不同產品線，這些產品的生產可以共用一些資源。

比如，我的產品都分為大、中、小三種分類。分別進行不同的加工

• 聲明抽象水果

public interface Fruit {String getName();String getSize();default void description() {System.out.println("產品名稱：" + getSize() + getName());}
}

• 聲明具體水果

public class BigApple implements Fruit {@Overridepublic String getName() {return "蘋果";}@Overridepublic String getSize() {return "大號";}
}public class MiddleApple implements Fruit {@Overridepublic String getName() {return "蘋果";}@Overridepublic String getSize() {return "中號";}
}public class SmallApple implements Fruit {@Overridepublic String getName() {return "蘋果";}@Overridepublic String getSize() {return "小號";}
}

public class BigBanana implements Fruit {@Overridepublic String getName() {return "香蕉";}@Overridepublic String getSize() {return "大號";}
}public class MiddleBanana implements Fruit {@Overridepublic String getName() {return "香蕉";}@Overridepublic String getSize() {return "中號";}
}public class SmallBanana implements Fruit {@Overridepublic String getName() {return "香蕉";}@Overridepublic String getSize() {return "小號";}
}

• 聲明抽象工廠

public abstract class AbstractFruitFactory {abstract Fruit bigFruit();abstract Fruit middleFruit();abstract Fruit smallFruit();
}

• 定義具體工廠

public class AppleFruitFactory extends AbstractFruitFactory{@OverrideFruit bigFruit() {return new BigApple();}@OverrideFruit middleFruit() {return new MiddleApple();}@OverrideFruit smallFruit() {return new SmallApple();}
}

public class BananaFruitFactory extends AbstractFruitFactory {@OverrideFruit bigFruit() {return new BigBanana();}@OverrideFruit middleFruit() {return new MiddleBanana();}@OverrideFruit smallFruit() {return new SmallBanana();}
}

增加工廠管理類

當抽象工廠的子類擴展時，調用方需要和各個子類工廠交互，在一定程度上違反了迪米特法則。
我們可以將工廠子類交由工廠管理類進行管理，調用方只需要和這個管理類交互即可

public final class FruitFactoryManager {private static Map<String, AbstractFruitFactory> register = new HashMap<>();static {register.put("apple", new AppleFruitFactory());register.put("banana", new BananaFruitFactory());}public static AbstractFruitFactory getFactory(String factoryCode) {return register.get(factoryCode);}
}

使用

public class Sample {public static void main(String[] args) {AbstractFruitFactory appleFactory = new AppleFruitFactory();Fruit smallApple = appleFactory.smallFruit();smallApple.description();Fruit middleApple = appleFactory.middleFruit();middleApple.description();Fruit bigApple = appleFactory.bigFruit();bigApple.description();AbstractFruitFactory bananaFactory = new BananaFruitFactory();Fruit smallBanana = bananaFactory.smallFruit();smallBanana.description();Fruit middleBanana = bananaFactory.middleFruit();middleBanana.description();Fruit bigBanana = bananaFactory.bigFruit();bigBanana.description();}
}