Question

I am learning Collections in CoreJava book and I found this code:

      List<String> a = new LinkedList<String>();

Now I wonder why this code isn’t like this:

LinkedList<String> a = new LinkedList<String>();

Why we declare a as List?

Answer 1

The code:

List<String> list = new LinkedList<String>();

is better than:

LinkedList<String> list = new LinkedList<String>();

This is because if you declared list as List and you found that the performance of the program is not good, you could change the code to:

List<String> list = new ArrayList<String>();

and see if the program runs faster. The beauty of this is that you can make that change without having to change the rest of the code.

As a conclusion, if possible, declare a reference as an interface (List is an interface):

List<String> list;

and you can easily switch the implementation (class ArrayList and class LinkedList are implementations of the interface List):

list = new LinkedList<String>();

or

list = new ArrayList<String>();