How to re-order Map items based on the user input?

Question

I am trying to do something similar to the Huffman tree. When I type zzzbbbbbbbbbaaaaacc, the Map I get is this : [a=5, b=9, c=2, z=3]

I think it orders it in alphabetical order but that is not what I want. I want to have the order like this : [z=3, b=9, a=5, c=2] (the user input starts with z, then b, then a, then c).

My code looks like this for now :

public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        String s = scan.nextLine();

        Queue<Character> fifo = new LinkedList<Character>(); 
        for (Character character : s.toCharArray()) {
            fifo.add(character);
        }
        List<String> distinctElements = s.chars().mapToObj(e -> Character.toString((char) e)).distinct()
                .collect(Collectors.toList());

        Map<Character, Long> characters = s.chars().distinct().mapToObj((e -> (char) e))
                .collect(Collectors.toMap(c -> c, c -> s.chars().filter(ch -> ch == c).count()));
        

Answer 1

You can use a toMap collector with a map constructor argument:

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Scanner;

import static java.util.stream.Collectors.toMap;

public class MapFromString {
    public static void main(String[] args) {
        try (Scanner scan = new Scanner(System.in)) {
            String s = scan.nextLine();

            Map<Character, Integer> map = s.chars()
                    .boxed()
                    .collect(
                        toMap(c -> Character.valueOf((char) c.intValue()), 
                              c -> 1, 
                              Integer::sum, 
                              LinkedHashMap::new));

            System.out.println(map);
        }
    }
}

Answer 2

You should be using a LinkedHashMap, this structure maintains the order of elements inserted into it.

This guide has some examples to see it in action: https://www.baeldung.com/java-linked-hashmap