Class object of generic class (java)
JavaGenericsJava Problem Overview
is there a way in java to get an instance of something like Class<List<Object>>
?
Java Solutions
Solution 1 - Java
how about
(Class<List<Object>>)(Class<?>)List.class
Solution 2 - Java
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);
Solution 3 - Java
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.
Solution 4 - Java
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.
Solution 5 - Java
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.
Solution 6 - Java
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.
Solution 7 - Java
List.class
the specific type of generics is "erased" at compile time.