我試圖將Abstract Factory Pattern與有界的類型化參數(shù)一起使用，示例如下：CageAbstractFactory.javapublic interface CageAbstractFactory {    public Cage<?> createCage();}CageFactory.javapublic class CageFactory {    public static Cage<?> getCage(CageAbstractFactory factory) {        return factory.createCage();    }}XxxCageFactory.java（Xxx = Lion，Rat等）public class XxxCageFactory implements CageAbstractFactory {    @Override    public Cage<Xxx> createCage() {        return new XxxCage();    }}籠子public abstract class Cage<T extends Animal> {     protected Set<T> cage = new HashSet<T>();    public abstract void add(T animal);    public void showAnimals() {        System.out.println(cage);    }}XxxCage.java（Xxx = Lion，Rat等）public class XxxCage extends Cage<Xxx> {    @Override    public void add(Xxx r) {        cage.add(r);    }}動(dòng)物.javapublic class Animal {    public String toString() {        return getClass().getSimpleName();    }   }class Rat extends Animal {}class Lion extends Animal {}AFP.java（主類）public class AFP {    public static void main(String[] args) {        Cage<?> rc = CageFactory.getCage(new RatCageFactory());        Cage<?> lc = CageFactory.getCage(new LionCageFactory());        rc.add(new Rat());        rc.showAnimals();        lc.add(new Lion());    }}在第rc.add(new Rat())OR行或rc.add(new Lion())以下錯(cuò)誤出現(xiàn)：The method add(capture#3-of ?) in the type Cage<capture#3-of ?> is not applicable for the arguments (Rat)似乎從Cage<?>到Cage<Rat>/的類型轉(zhuǎn)換錯(cuò)誤Cage<Lion>但是問題是CageFactory.getCage(CageAbstractFactory factory)返回Cage<?>是僅在運(yùn)行時(shí)通過選擇CageAbstractFactory作為參數(shù)傳遞的類（即LionCageFactoryOR RatCageFactory）來決定的。