泛型类的类对象（java）

Question

java中有没有办法获取类似Class<List<Object>>的实例？

Answer 1

怎么样

(Class<List<Object>>)(Class<?>)List.class

Answer 2

public final class ClassUtil {
    @SuppressWarnings("unchecked")
    public static <T> Class<T> castClass(Class<?> aClass) {
        return (Class<T>)aClass;
    }
}

Now you call:

Class<List<Object>> clazz = ClassUtil.<List<Object>>castClass(List.class);

Answer 3

Because of type erasure, at the Class level, all List interfaces are the same. They are only different at compile time. So you can have Class<List> as a type, where List.class is of that type, but you can't get more specific than that because they aren't seperate classes, just type declarations that are erased by the compiler into explicit casts.

Answer 4

As mentioned in other answers, Class represents an erased type. To represent something like ArrayList<Object> , you want a Type . An easy way of getting that is:

new ArrayList<Object>() {}.getClass().getGenericSuperclass()

The generic type APIs introduced in 1.5 are relatively easy to find your way around.

Answer 5

You could use Jackson's ObjectMapper

ObjectMapper objectMapper = new ObjectMapper();
CollectionType listType = objectMapper.getTypeFactory().constructCollectionType(List.class, ElementClass.class)

No unchecked warnings, no empty List instances floating around.

Answer 6

You can get a class object for the List type using:

Class.forName("java.util.List")

or

List.class

But because java generics are implemented using erasures you cannot get a specialised object for each specific class.

Answer 7

List.class

特定类型的泛型在编译时被“擦除”。