Literatura: poglavlje 3 iz knjige
https://sophia.javeriana.edu.co/~cbustaca/docencia/DSBP-2018-01/recursos/Erich%20Gamma,%20Richard%20Helm,%20Ralph%20Johnson,%20John%20M.%20Vlissides-Design%20Patterns_%20Elements%20of%20Reusable%20Object-Oriented%20Software%20%20-Addison-Wesley%20Professional%20(1994).pdf