通用類的初始化

Question

這是我的課：

public class FoodSet<T extends ConcreteFood>{ 
    public List<T> food = new ArrayList<T>(); 
    public FoodSet() 
    { 
     /* 
     * FoodType is an enum containing food types e.g: rice, pork, beef ... 
     */ 
     for(FoodType foodType : FoodType.values()) 
     { 
      /* 
      * 1(*) 
      */
      food.add((T)new ConcreteFood(foodType,0)) 
     }  
    } 
} 

而在1（*）的問題是，如何初始化這份名單中，有「T」型？ 現在我用ConcreteFood初始化它，給出參數foodType和amount， 但我的目標是用T來啓動這個列表，它擴展了ConcreteFood。 ConcreteFood的每個子類都可以獲得食物類型和食物數量。 我只是想用適當的ConcreteFood子類初始化這個列表，並且 init每個ConcreteFood對象的foodType和count = 0。 我應該怎麼做？

Answer 1

這不是你想要的。您需要一個工廠類來爲您創建ConcreteFood的實例。

public class FoodFactory { 
    private static final FoodFactory INSTANCE = new FoodFactory(); 

    private FoodFactory() {} 

    public static FoodFactory getInstance() { return INSTANCE; } 

    public Food create(FoodType type) { 
     // Put the type checks here 
    } 
} 

我不在乎你的命名。 「ConcreteFood」？聽起來不開胃。爲什麼不FoodCategory？

Answer 2

你可以使用你的FoodTypeenum作爲工廠：

public static class ConcreteFood { 
} 

public static class Bacon extends ConcreteFood { 
}; 

public static class SavoyCabbage extends ConcreteFood { 
}; 

enum FoodType { 
    Pork { 
    @Override 
    public ConcreteFood makeNew() { 
     return new Bacon(); 
    } 
    }, 
    Cabbage { 
    @Override 
    public ConcreteFood makeNew() { 
     return new SavoyCabbage(); 
    } 
    }; 

    public abstract ConcreteFood makeNew(); 
} 

public static class FoodSet { 
    public List<ConcreteFood> food = new ArrayList<ConcreteFood>(); 

    public FoodSet() { 
    /* 
    * FoodType is an enum containing food types e.g: rice, pork, beef ... 
    */ 
    for (FoodType foodType : FoodType.values()) { 
     /* 
     * 1(*) 
     */ 
     //food.add((T) new ConcreteFood(foodType, 0)) 
     food.add(foodType.makeNew()); 
    } 
    } 
} 

Answer 3

針對OP的回答是：你真的不應該想這種方式。我建議你通過正確的混凝土工廠到你的FoodSet。

抽象工廠：

public interface FoodFactory<T extends ConcreteFood> { 
    public T create(FoodType type); 
} 

混凝土廠，每ConcreteFood

public class BagFoodFactory implements FoodFactory<BagFood> { 
    private static final BagFoodFactory INSTANCE = new BagFoodFactory(); 

    private BagFoodFactory() {} 

    public static FoodFactory<BagFood> getInstance() { return INSTANCE; } 

    public BagFood create(FoodType type) { 
     return new BagFood(type, 0); 
    } 
} 

子一個使用工廠在FoodSet

public class FoodSet<T extends ConcreteFood> { 
    public List<T> food = new ArrayList<T>(); 

    public FoodSet(FoodFactory<T> factory) { 
     for (FoodType foodType : FoodType.values()) { 
      food.add(factory.create(foodType)); 
     } 
    } 
} 

將正確的工廠構造函數（無論如何，你知道你需要哪一個）。

class Sack 
{ 
    public FoodSet<BagFood> bagFoodSet 
      = new FoodSet<BagFood>(BagFoodFactory.getInstance()); 
}