Get duplicate from collection

Question

Hi All,
I've made one method that pulling out duplicate objects from Vector.
But really I don't like this way; looping for(int i=0; i<column.size(); i++) because the vector size is very big and it makes bad performance.
Can anybody give me some better idea?
public Set getDuplicate(Vector column)
     Set unique = new HashSet();
     Set dupResult = new HashSet();
     Object obj;
     for(int i=0; i<column.size(); i++)
          obj = column.get(i);
          if(unique.contains(obj))
               if(!dupResult.contains(obj))
                    dupResult.add(obj);
          }else
               unique.add(obj);
     return dupResult;
}

Answer 1

This should give better performance. I am not sure how to do it
without the for loop though.
public Set getDuplicate(Vector column)
  Set unique = new HashSet();
  Set dupResult = new HashSet();
  Object obj;
  for(int i=0; i<column.size(); i++)
    obj = column.get(i);
    if (unique.add(obj) == false) {
      dupResult.add(obj);
  return dupResult;
}