Playing with List

Confusion which I have first time and require attention :

1. Sometimes we confused about List that it is a class and try to create a Object of it.(First time I did this :) ). After that I realize that List is a interface.
2. Use generic types whenever using any collection like List. Why ? According to Java doc : Generics add stability to your code by making more of your bugs detectable at compile time. (I was not aware of this first time.)

   import java.util.ArrayList;

   import java.util.Collection;

   import java.util.Iterator;

   import java.util.List;

   import java.util.ListIterator;

   public class TestClass implements List<String>{

       public static void main(String ...strings){

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

       list.add(null);      null is allowed in List.

       list.add("Ram");

       list.add("Ram"); duplicate elements are allowed in List.

       list.add(1,"Shyam"); inserts "Shyam" at position 1 and also it change index of all elements after that index.

          list.get(0);

     System.out.println(list);

     System.out.println(list.size());

   

    }

}