在Factory Method模式中，父類決定實例的生成方式，但并不決定所要生成的具體的類，具體的處理全部交給子類負責，這樣就可以將生成實例的框架和實際負責生成實例的類解耦

Factory Method模式UML

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Factory

public abstract class Factory {
    public final Product create(String owner) {
        Product p = createProduct(owner);
        registerProduct(p);
        return p;
    }

    protected abstract Product createProduct(String owner);
    protected abstract void registerProduct(Product product);
}

IDCardFactory

public class IDCardFactory extends Factory {
    private List owners = new ArrayList();
    @Override
    protected Product createProduct(String owner) {
        return new IDCard(owner);
    }

    @Override
    protected void registerProduct(Product product) {
        owners.add(((IDCard)product).getOwner());
    }
}

Product

public abstract class Product {
    public abstract void use();
}

IDCard

public class IDCard extends Product {
    private String owner;
    IDCard(String owner) {
        System.out.println("制作" + owner + "的ID卡。");
        this.owner = owner;
    }
    @Override
    public void use() {
        System.out.println("使用" + owner + "的ID卡");
    }

    public String getOwner() {
        return owner;
    }
}

Main

public class Main {

    public static void main(String[] args) {
    // write your code here
        Factory factory = new IDCardFactory();
        Product card1 = factory.create("小明");
        Product card2 = factory.create("小紅");
        card1.use();
        card2.use();

        System.out.println();
    }
}