List vs ArrayList

Question

List> listeners = new List>();

Why the line above fails with:

Cannot in

Answer 1

The proper way is:

List<EventHandler<E>> listeners = new ArrayList<EventHandler<E>>();

• refer to an object by its interface (List)
• instantiate the object with its concrete type (ArrayList) (interfaces can't be instantiated)

Answer 2

List is an interface, you can't instantiate an interface.

Answer 3

List cannot be instantiated, as it's just an interface.

However, you potentially have another problem as well.

Do you really have a class called 'E'? If you do, well, you shouldn't without a very good reason.

Single letters such as E and T are pretty much exclusively used to denote a generic type parameter. Read it as: "This is a general description of how to make a class or method, without any reference to any specific type - you can parameterize this class by any legal reference type".

So even classes like ArrayList<T> cannot be instantiated - because they are generic "recipes" for classes, not real concrete classes.

Answer 4

The List<T> is an interface so you can't instantiate it where as ArrayList<T> is a concrete class which is an implementation of List<T>.

Answer 5

List is only an Interface which is implemented by ArrayList

see: http://download.oracle.com/javase/6/docs/api/java/util/List.html

Answer 6

List is an interface and you can not create an instance of an interface

try

List<EventHandler<E>> listeners = new ArrayList<EventHandler<E>>();