How do I remove repeated elements from ArrayList?
I have an ArrayList of Strings , and I want to remove repeated strings from it. How can I do this?
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 :
List<String> al = new ArrayList<>();
// add elements to al, including duplicates
Set<String> hs = new HashSet<>();
hs.addAll(al);
al.clear();
al.addAll(hs);
Of course, this destroys the ordering of the elements in the ArrayList .
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.
In Java 8:
List<String> deduped = list.stream().distinct().collect(Collectors.toList());
Please note that the hashCode-equals contract for list members should be respected for the filtering to work properly.
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