FactoryMethodパターンの例を作ろうとして霧の中に迷い込んだ

Main.java

import java.util.Arrays;
import java.util.List;

public class Main {

    public static void main(String[] args) {

        List<Menu> orders = Arrays.asList(Menu.French, Menu.Sushi, Menu.French, Menu.Sushi);
        orders.forEach(order -> ChefFactoryManager.build().assignChef(order).cook());

    }
}

class ChefFactoryManager {
    static ChefFactory cf = null;

    public static ChefFactory build() {
        if (cf == null) {
            cf = new ChefFactory();
        }
        return cf;
    }
}

class ChefFactory {
    private ConcreteFrenchChefCreater french;
    private ConcreteSushiChefCreater sushi;

    Chef assignChef(Menu menu) {
        ChefCreater creator = null;
        switch (menu) {
            case Sushi:
                if (this.sushi == null) {
                    this.sushi = new ConcreteSushiChefCreater();
                }
                creator = this.sushi;
                break;
            case French:
                if (this.french == null) {
                    this.french = new ConcreteFrenchChefCreater();
                }
                creator = this.french;
                break;
        }
        if (creator == null) {
            return null;
        }
        return creator.assign();
    }

}

enum Menu {
    Sushi,
    French
}

// 何料理かわかんないけどキッチンに立っているシェフ達を抽象化したインターフェース
interface Chef {
    void cook();
}

// 寿司職人
class ConcreteSushiChef implements Chef {
    @Override
    public void cook() {
        System.out.println("Sushi!!!");
    }
}

// フレンチの鉄人
class ConcreteFrenchChef implements Chef {
    @Override
    public void cook() {
        System.out.println("French!!!");
    }
}

// シェフをアサインするFactoryMethodクラス
abstract class ChefCreater {
    public Chef assign() {
        Chef chef = callChef();
        registerChef(chef);
        return chef;
    }
    protected abstract Chef callChef();
    protected abstract void registerChef(Chef chef);
}

class ConcreteSushiChefCreater extends ChefCreater {
    @Override
    protected Chef callChef() {
        return new ConcreteSushiChef();
    }

    @Override
    protected void registerChef(Chef chef) {
        System.out.println("寿司職人がアサインされた!!!");
    }
}

class ConcreteFrenchChefCreater extends ChefCreater {
    @Override
    protected Chef callChef() {
        return new ConcreteFrenchChef();
    }
    @Override
    protected void registerChef(Chef chef) {
        System.out.println("フレンチの鉄人がアサインされた!!!");
    }
}