Java – Remove Duplicate Object in Collection

import java.util.*;

public class RemoveDuplicate {

    public static void main(String[] args) {
          ArrayList<String> arrayList1 = new ArrayList<String>();

          arrayList1.add("A");
          arrayList1.add("A");
          arrayList1.add("B");
          arrayList1.add("B");
          arrayList1.add("B");
          arrayList1.add("C");

          for (int i=0; i< arrayList1.size(); i++)
          {
            System.out.println("Having Duplicate Objects :"+arrayList1.get(i));
          } 

          Set<String> s=new TreeSet<String>();
          s.addAll(arrayList1);

          Iterator it=s.iterator();
          while (it.hasNext())
          {
            System.out.println("No Duplicate :"+(String)it.next());
          } 

    }
}