Question

What’s the difference between defining a arraylist like this:

List list = new LinkedList(); 

and like this?

LinkedList list = new LinkedList();

Answer 1

As other answers have suggested, List is the interface, and LinkedList is the actual implementation type. If, for example, you later decided that you wanted to use an ArrayList, you could type:

List list = new ArrayList();

because ArrayList declares the interface List. The downside is that if you want to call any methods of an ArrayList/LinkedList/(Other classname that has methods that aren’t in list) later that are not part of the List interface (this probably won’t be an issue), you would have to check if it really was an ArrayList, etc. and cast it to those types. Like this:

ArrayList arrayList = (ArrayList) list;

*only after checking that it really is an ArrayList, otherwise you throw an exception.