How to sort an ArrayList by its elements size in Java?

Question

So I have a List<String> L1 = new ArrayList<>() with the following strings as elements:

• l, l, u, u.
• r, u, d, l, d, l, u.
• l, u, d, r, r, r, r, r, u, d.
• l, u.
• l, u, r.

How do I sort the list by its element's size so that in the final state L1 should be like this:

• l, u.
• l, u, r.
• l, l, u, u.
• r, u, d, l, d, l, u.
• l, u, d, r, r, r, r, r, u, d.

I have tried using Collections.sort, but that sorts alphabetically, which is obviously not what I want.

Answer 1

I think what you are looking for is Collections.sort(java.util.List, java.util.Comparator). With it you can specify a custom Comparator that compares the strings based on length instead of alphabetical relationship.

Something like this:

List<String> stringList = new ArrayList<String>();

// Fill the list

Comparator<String> stringLengthComparator = new Comparator<String>()
    {
        @Override
        public int compare(String o1, String o2)
        {
            return Integer.compare(o1.length(), o2.length());
        }
    };

Collections.sort(stringList, stringLengthComparator);