JAVA-Generics(5)

ムカデ形変換

ギネスタイプと元のタイプとの間の変形は望ましくない.

Box<Object> objBox = null;
Box box = (Box)objBox;		//ok. 지네릭타입 -> 원시타입.   경고발생
objBox = (Box<Object>)box;	//ok. 원시타입   ->지네릭 타입. 경고발생

Genericタイプとnon-genericタイプの間のタイプ変換は常に可能である.警告だけが発生します.

Box<Object> objBox = null;
Box<String> strBox = null;

objBox = (Box<Object>)strBox;	//에러. Box<String> -> Box<Object>
strBox = (Box<String>)objBox;	//에러. Box<Object> -> Box<String>

ワイルドカードタイプはGenericタイプ

に変換可能

Box<Object>			objBOX = (Box<Object>) new Box <String>();	//에러, 형변환 불가능
Box<? extends Object> wBox = (Box<? extends Object>)new Box<String>();	//ok
Box<? extends Object> wBox = new Box<String>();

//매개변수로 FruitBox<Fruit>, FruitBox<Apple>, FruitBox<Grape> 등이 가능
static Juice makeJuice(FruitBox<? extends Fruit> box){ ... }

FruitBox<? extends Fruit> box = new FruitBox<Fruit>();	//ok
FruitBox<? extends Fruit> box = new FruitBox<Apple>();	//ok