将泛型作为参数传递给Java？

Question

Is it possible to save a Type in a variable,
in order to instantiate a List of this type?

//something like that
Type type = Boolean;
List<type> list = new List<type>();
list.add(true);

Answer 1

For the first requirement, you are looking for Class :

Class type = Boolean.class;

However, I don't think the seconds requirement is feasible, since generic types only exist at compile time:

List<type> list = new List<type>(); // invalid code

You can, however, work with List<Object> . It will accept Boolean objects. Whether this will buy you anything untlimately depends on your use case.

Answer 2

Generic is a compile time feature, not run time, so you cannot use variable to determine the generic type, even using NPE's note (using Class ) will not compile:

Class<?> type = Boolean.class;
// can't do that...
List<type> list = new List<type>();
list.add(true);

Answer 3

In second case why do you want to use generics when type is unknown? You can better use non-generic arraylist ( used before jdk 5).

   List a = new ArrayList();
   a.add(object);

This style is still supported by higher versions and even generics style gets converted to this form after compilation. You will get warning in above code which you can suppress.