Java演员：哪个更好 - 命令式还是程序化方式？

Question

I have seen that there are two ways to cast an object in Java:

List<Object> l = new ArrayList();
ArrayList<Object> first = (ArrayList<Object>) l;
ArrayList<Object> second = ArrayList.class.cast(l);

Which is better and why?

Answer 1

The better method is the most readable. If you already know what class to do the type cast, use (ClassToUpcast) object . If you don't know the class but you have the Class<ClassToUpcast> clazz object, then use clazz.cast(object) .

Answer 2

ArrayList<Object> second = ArrayList.class.cast(l); should give you a compiler warning as this reflective operation is not able to check the type parameter of the list.

ArrayList<Object> first = (ArrayList<Object>) l; on the other hand is a non-reflective operation for which the compiler can prove that the type parameters of List and ArrayList are the same and therefore that this is a safe operation.

So it should be clear which one is to prefer.