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

Code:

List<String> duplicatList = new ArrayList<String>();
duplicatList = Arrays.asList("AA","BB","CC","DD","DD","EE","AA","FF");
//above AA and DD are duplicate
Set<String> uniqueList = new HashSet<String>(duplicatList);
duplicatList = new ArrayList<String>(uniqueList); //let GC will doing free memory
System.out.println("Removed Duplicate : "+duplicatList);

Note: Definitely, there will be memory overhead.

Answer 2

If you are using model type List< T>/ArrayList< T> . Hope,it's help you.

Here is my code without using any other data structure like set or hashmap

for (int i = 0; i < Models.size(); i++){
for (int j = i + 1; j < Models.size(); j++) {       
 if (Models.get(i).getName().equals(Models.get(j).getName())) {    
 Models.remove(j);
   j--;
  }
 }
}

Answer 3

Here's a way that doesn't affect your list ordering:

ArrayList l1 = new ArrayList();
ArrayList l2 = new ArrayList();

Iterator iterator = l1.iterator();

while (iterator.hasNext()) {
    YourClass o = (YourClass) iterator.next();
    if(!l2.contains(o)) l2.add(o);
}

l1 is the original list, and l2 is the list without repeated items (Make sure YourClass has the equals method according to what you want to stand for equality)

Answer 4

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 5

Java 8 streams provide a very simple way to remove duplicate elements from a list. Using the distinct method. If we have a list of cities and we want to remove duplicates from that list it can be done in a single line -

 List<String> cityList = new ArrayList<>();
 cityList.add("Delhi");
 cityList.add("Mumbai");
 cityList.add("Bangalore");
 cityList.add("Chennai");
 cityList.add("Kolkata");
 cityList.add("Mumbai");

 cityList = cityList.stream().distinct().collect(Collectors.toList());

How to remove duplicate elements from an arraylist

Answer 6

        List<String> result = new ArrayList<String>();
        Set<String> set = new LinkedHashSet<String>();
        String s = "ravi is a good!boy. But ravi is very nasty fellow.";
        StringTokenizer st = new StringTokenizer(s, " ,. ,!");
        while (st.hasMoreTokens()) {
            result.add(st.nextToken());
        }
         System.out.println(result);
         set.addAll(result);
        result.clear();
        result.addAll(set);
        System.out.println(result);

output:
[ravi, is, a, good, boy, But, ravi, is, very, nasty, fellow]
[ravi, is, a, good, boy, But, very, nasty, fellow]