public class testList {

     public static void main(String[] args){

         java.util.List<String> ls = new java.util.ArrayList<>();

         ls.add("A");

         ls.add("B");

         ls.add("C");

         String[] str = {"A","B","C","D"};

         for(int i=0;i<str.length;i++){

             ls.add(str[i]);

         }

         java.util.Set<String> set = new java.util.TreeSet<>(ls);

         java.util.List<String> lsr = new java.util.ArrayList<>();

         lsr.addAll(set);

         System.out.println(lsr.toString());

     }

 }