How do I remove repeated elements from ArrayList?

Question

I have an ArrayList<String>, and I want to remove repeated strings from it. How can I do this?

Answer 1

If you don't want duplicates in a Collection, you should consider why you're using a Collection that allows duplicates. The easiest way to remove repeated elements is to add the contents to a Set (which will not allow duplicates) and then add the Set back to the ArrayList:

Set<String> set = new HashSet<>(yourList); yourList.clear(); yourList.addAll(set); 

Of course, this destroys the ordering of the elements in the ArrayList.

Answer 2

Although converting the ArrayList to a HashSet effectively removes duplicates, if you need to preserve insertion order, I'd rather suggest you to use this variant

// list is some List of Strings Set<String> s = new LinkedHashSet<>(list); 

Then, if you need to get back a List reference, you can use again the conversion constructor.