package ArchitectureTest; import java.util.HashMap; import java.util.Map; public class Customers { static private Customers theInstance = null; private Map<String, Customer> customers = new HashMap<>(); private Customers() { } static public Customers getInstance() { if (theInstance == null) { theInstance = new Customers(); } return theInstance; } public Map<String, Customer> getCustomers() { return customers; } }