Java group anagrams without sorting array

Question

I see the below solution to a popular question to group anagrams. I want to achieve it without sorting. I ran through the solution in my IDE to debug and understand step by step but I just can't seem to figure out what we are doing in the lines I have mentioned below on what we are doing in the algorithm. The IDE just shows a bunch of commas.

What can I try next?

    public List<List<String>> groupAnagrams(String[] strs) {
    List<List<String>> result = new ArrayList<List<String>>();
 
    HashMap<String, ArrayList<String>> map = new HashMap<String, ArrayList<String>>();
    for(String str: strs){
        char[] arr = new char[26];
        for(int i=0; i<str.length(); i++){
            arr[str.charAt(i)-'a']++; -- what are we doing here?
        }
        String ns = new String(arr); -- what does ns actually have?
 
        if(map.containsKey(ns)){
            map.get(ns).add(str);
        }else{
            ArrayList<String> al = new ArrayList<String>();
            al.add(str);
            map.put(ns, al);
        }
    }
 
    result.addAll(map.values());
 
    return result;
}

Answer 1

arr[str.charAt(i)-'a']++; -- what are we doing here? 

Just mapping char 'a' to 'z' to index 0 to 26 in arr and incrementing its count. So a string like 'aaab' will translate to 'arr[0] = 3 and arr[1]=1'

String ns = new String(arr); -- what does ns actually have?

Converting arr of char to string. words which are anagram will have same values of count in arr and will result in same string ns.