How do I remove repeated elements from ArrayList?

Question

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

Answer 1

Suppose we have a list of String like:

List strList = new ArrayList<>(5);
// insert up to five items to list.        

Then we can remove duplicate elements in multiple ways.

Prior to Java 8

List deDupStringList = new ArrayList<>(new HashSet<>(strList));

Note: If we want to maintain the insertion order then we need to use LinkedHashSet in place of HashSet

Using Guava

List deDupStringList2 = Lists.newArrayList(Sets.newHashSet(strList));

Using Java 8

List deDupStringList3 = strList.stream().distinct().collect(Collectors.toList());

Note: In case we want to collect the result in a specific list implementation e.g. LinkedList then we can modify the above example as:

List deDupStringList3 = strList.stream().distinct()
                 .collect(Collectors.toCollection(LinkedList::new));

We can use parallelStream also in the above code but it may not give expected performace benefits. Check this question for more.