我試圖將Abstract Factory Pattern與有界的類型化參數一起使用，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())以下錯誤出現：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>/的類型轉換錯誤Cage<Lion>但是問題是CageFactory.getCage(CageAbstractFactory factory)返回Cage<?>是僅在運行時通過選擇CageAbstractFactory作為參數傳遞的類（即LionCageFactoryOR RatCageFactory）來決定的。
2 回答
慕田峪9158850
TA貢獻1794條經驗 獲得超8個贊
不要使用wildcard ?作為
public static Cage<?> getCage(CageAbstractFactory factory) {
return factory.createCage();
}
但是使用通用
public static <T extends Animal> Cage<T> getCage(CageAbstractFactory factory) {
return factory.createCage();
}
慕標5832272
TA貢獻1966條經驗 獲得超4個贊
您還需要對進行概括CageAbstractFactory：
public interface CageAbstractFactory<T> {
public Cage<T> createCage();
}
public class CageFactory {
public static <T> Cage<T> getCage(CageAbstractFactory<T> factory) {
return factory.createCage();
}
}
public class XxxCageFactory implements CageAbstractFactory<Xxx> {
@Override
public Cage<Xxx> createCage() {
return new XxxCage();
}
}
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