Playing with Map

My first time confusion about Map :

1. Map is a interface not a class, so we can't create a Object of Map.
2. Map are quite different from List , they contains key - value pair.

   import java.util.Collection;

   import java.util.HashMap;

   import java.util.Map;

   import java.util.Set;

      public class TestClass implements Map<String,String>{

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

              Map<String,String> map = new HashMap<String,String>();

              map.put("1" , "first");

              map.put("2", "second");

              map.put("2", null); Map can't have duplicate elements last value override previous value.

              map.put(null, null); Key and Value both can be null.

         System.out.println(map);

         System.out.println(map.size());

     

    }

}

Output : 

{null=null, 2=null, 1=first}

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