I have an ArrayList<String>, and I want to remove repeated strings from it. How can I do this?
40 Answers
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.
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.
Suppose we have a list of String like:
List<String> 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<String> 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
