我尝试使用 this answer 中给出的代码.我这样做了:
public class ListClass<T> {
private class ObjectFactory<T> {
//This should the the class of generic type T which is what I need
public final Class<T> cls;
@SuppressWarnings ("unchecked")
public ObjectFactory()
{
//This three lines are from the linked answer - I don't really understand them
Type type = getClass().getGenericSuperclass();
ParameterizedType paramType = (ParameterizedType) type; //java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType
cls = (Class<T>) paramType.getActualTypeArguments()[0];
}
public T createNew(... some parameters ...) {
return (T)new Expression(cls, "new", new Object[]{... some parameters ...}).getValue();
}
}
public final ObjectFactory<T> factory = new ObjectFactory<T>();
public generateItem() {
//let add() be method that adds item of type T to this list
this.add(factory.createNew(... some parameters ...));
}
}
我哪里错了?
最佳答案
此技术仅在使用如下具体参数对类进行参数化时才有效:
class Sub extends Super<String> {}
然后通过扩展:
new Super<String>() {}
但不是这样:
class Sub<T> extends Super<T> {}
不是这样的:
<T> Super<T> m() {
return new Super<T>() {};
}
使用能力getActualTypeArguments
是类的属性,而不是实例,因此类需要实际类型参数才能使用它。
根据您的编辑,我建议您为此创建一个辅助例程:
static <T> Class<T> getActualTypeArgument(Class<?> clazz, int i) {
Type superclazz = getClass().getGenericSuperclass();
ParameterizedType paramType = (ParameterizedType) superclazz;
@SuppressWarnings("unchecked")
final Class<T> actual =
(Class<T>) paramType.getActualTypeArguments()[i];
return actual;
}
然后在 ListClass
上使用它:
class ListClass<T> {
private ObjectFactory<T> factory = new ObjectFactory<T>(
getActualTypeArgument(this.getClass(), 0));
}
并创建 ListClass
例如以下方式:
ListClass<GameObject> list =
new ListClass<GameObject>() {};
也考虑传递 Class<T>
在:
class ListClass<T> {
private ObjectFactory<T> factory;
ListClass<T>(Class<T> type) {
factory = new ObjectFactory(type);
}
static <T> ListClass<T> of(Class<T> type) {
return new ListClass<T>(type);
}
}
ListClass<GameObject> list =
ListClass.of(GameObject.class);
关于java - 尝试获取泛型类型类时出现 ClassCastException,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29988180/