What is the output of the following program(HashSet)? : Questions « Utility Classes « SCJP

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import java.util.*;
      public class MainClass {
       public static void main(String args[]) {
        HashSet set = new HashSet();
        String s1 = "abc";
        String s2 = "def";
        String s3 = "";
        set.add(s1);
        set.add(s2);
        set.add(s1);
        set.add(s2);
        Iterator i = set.iterator();
        while(i.hasNext()){
         s3 += (String) i.next();
        }
        System.out.println(s3);
       }
      }