title: Merging ArrayList of Model elements without duplicates
body: <p>Hi I have two array list List l1 and List l2, Name,age,sex,uniqID,marks are the data inside the lists. I want to join l1 and l2 without duplicates.uniqID is unique for each student. I have been looping through all the elements and comparing each and every element. But My list would have around 20k items so the looping is taking too much time. I have tried 
  <a href="https://stackoverflow.com/questions/16520046/how-to-merge-two-arraylists-without-duplicates">all the answers from this post</a> nothing worked for me. Any suggestions.?</p>