public class KeyValueLazySingleton {
    private final static String KEY = "FUCKING_KEY_FOR_INSTANCE";

    private static KeyValueLazySingleton INSTANCE;

    private final Map<Object, Object> kv = new HashMap<>();

    private KeyValueLazySingleton() {
        init();
    }

    public static KeyValueLazySingleton getInstance() {
        if (kv.containsKey(KEY))
            return kv.get(KEY);

        synchronized (KeyValueLazySingleton.class) {
            if (kv.containsKey(KEY))
                return kv.get(KEY);

            INSTANCE = new KeyValueLazySingleton();
            return INSTANCE;
        }
    }

    private void init() {
        kv.put("one", "a");
    kv.put(BigInteger.valueOf(100), new Object());
    kv.put(KEY, this);
    }

    public Object getValueByKey(Object key) {
        return kv.get(key);
    }
}