Remove duplicates from ArrayLists

Question

I have an ArrayList of custom objects. I want to remove duplicate entries.

The objects have three fields: title, subtitle, and id. If a subtitle occurs multiple times, I only need the first item with thats subtitle (ignore the remaining object with that subtitle).

Answer 1

You can put the content of the ArrayList in a TreeSet using a custom Comparator which should return 0 if the two subtitles are the same. After that you can convert the Set in a List and have the List without "duplicates". Here is an example for Object, of course you should use the correct class and logic.

public void removeDuplicates(List<Object> l) {
    // ... the list is already populated
    Set<Object> s = new TreeSet<Object>(new Comparator<Object>() {

        @Override
        public int compare(Object o1, Object o2) {
            // ... compare the two object according to your requirements
            return 0;
        }
    });
            s.addAll(l);
    List<Object> res = Arrays.asList(s.toArray());
}

Answer 2

List list = (...);

//list may contain duplicates.

//remove duplicates if any
Set setItems = new LinkedHashSet(list);
list.clear();
list.addAll(setItems);

You may need to override "equals()" so that 2 elements are considered equals if they have the same subtitle (or tite and subtitle maybe ?)