Question

Possible Duplicate:
Why should the interface for a Java class be prefered?

In Java, is there a difference between these two lines? If so, what is it, and when should I use either one? Is there a preferred convention?

Note that ArrayList implements List.

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

ArrayList<String> bunchOfStrings = new ArrayList<String>();

Answer 1

In both case you are instantiating an ArrayList. The difference is that in the first case you are referring it as a List (the interface that ArrayList implements ), so you don’t have access to specific method of ArrayList class, but only interfaces method.

use thi first:

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

This way you can switch different List implementation (ArrayList, Vector):

public class AClass(){
   List<String> bunchOfStrings;

   public List<String> getList(){
        bunchOfStrings = new ArrayList<String>();
        //or you can switch to : bunchOfStrings = new Vector<String>();
        return bunchOfString;
   }
}