How to get unique values in List

Question

I have 2 text files with data. I am reading these files with BufferReader and putting the data of one column per file in a List<String>.

I have duplicated data in each one, but I need to have unique data in the first List to confront with the duplicated data in the second List.

How can I get unique values from a List?

Answer 1

It can be done one one line by using an intermediate Set:

List<String> list = new ArrayList<>(new HashSet<>(list));

In java 8, use distinct() on a stream:

List<String> list = list.stream().distinct().collect(Collectors.toList());

Alternatively, don't use a List at all; just use a Set (like HashSet) from the start for the collection you only want to hold unique values.

Answer 2

Convert the ArrayList to a HashSet.

List<String> listWithDuplicates; // Your list containing duplicates
Set<String> setWithUniqueValues = new HashSet<>(listWithDuplicates);

If for some reason, you want to convert the set back to a list afterwards, you can, but most likely there will be no need.

List<String> listWithUniqueValues = new ArrayList<>(setWithUniqueValues);