Нужно вывести значения в таком виде (описано в коменарии)используя HashMap

public class ProductMain {
    public static void main(String[] args) {
        Commodity commodity1 = new Commodity("PC", 50000, "Technology");
        Commodity commodity2 = new Commodity("Locked Door", 14000, "Custom");
        Commodity commodity3 = new Commodity("Computer Desk", 20000, "Housing");
        Commodity commodity4 = new Commodity("Computer Mouse", 1000, "Technology");
        Commodity commodity5 = new Commodity("Computer Desk", 8000, "Housing");
        Commodity commodity6 = new Commodity("Locked Door", 15000, "Custom");
        Commodity commodity7 = new Commodity("Zzz", 10000, "Housing");
        // Technology:
        // - PC
        // - Computer Mouser
        // Custom:
        // - Locked Door
        // - Locked Door
        // Housing:
        // - Computer Desk
        // - Computer Desk
        // - Zzz
        Commodity[] commodities = new Commodity[]{commodity1, commodity2, commodity3, commodity4, commodity5, commodity6,commodity7};
        Map<String, List<String>> productInitials = new HashMap<>();
        List<Commodity> list = new ArrayList<>();