LinkedList different implementations

Question

I have seen 2 valid declarations of the LinkedList class in Collections Framework in Java.

1. LinkedList a = new LinkedList();
2. Queue a = new LinkedList();

What exactly is the difference between these 2 implementations?

Answer 1

Queue is an interface which LinkedList class implements.

In Your first case you a is a LinkedList reference to a LinkedList object. In the latter, a is a Queue interface reference pointing to a LinkedList object so, in this last case you will be only able to execute those service of LinkedList which are included in Queue interface.

Answer 2

There is just one implementation in your code: LinkedList.

Queue is one of the multiple interfaces implemented by LinkedList class.