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Opt greseli de design care ne pot afecta aplicatia

Am inceput sa studiez design patterns si am inceput cu o carte de a celor de la Gof (Gang of Four). In aceasta carte am gasit opt greseli de design care ne pot afecta aplicatia:
  1. Crearea unui obiect folosind numele unei clase explicit. In acest fel ajungem sa fim legati direct de o anumita implementare. Pentru a evita acest lucru putem sa folosim o interfata, iar instanta sa o cream in mod indirect, de exemplu printr-un factory.
  2. Dependinte directe fata de sistemul hardware sau software. In cazul in care aplicatia noastra depinde in mod direct de anumite resurse ale sistemului portabilitatea scade in mod direct. Pentru aceaste cazuri putem sa incercam sa folosim un patern precum bridge, pentru a scadea dependintele.
  3. Dependintele fata de o anumita operatie. Cand specificam o anumita operatie, limitam ca lucrurile sa se intample intr-o singura varianta si numai una. Modific─ârile care o sa apara in viitor o sa necesite mai mult timp, deoarece totul este hard-codat.
  4. Dependinta fata de algoritm. De obicei pe parcursul dezvolt─ârii unei aplicatii un algoritm se schimba, din aceasta cauza algoritmii ar trebuii sa fie izolati si schimbati cu usurinta.
  5. Extinderea functionalitatilor prin subclase. In momentul in care trebuie sa adaugam o noua functionalitate, putem foarte simplu sa mostenim din clasa parinte si sa adaugam o noua functionalitate. Dar acest lucru implica sa cunoastem foarte bine clasa de baza, iar in timp poate sa duca la existenta unui numar foarte mari de clase. Acest lucru se poate rezolva prin delegation si composition. Aceste doua mecanisme ne permite sa adaugam functionalitati fara sa avem o inlantuire de subclase.
  6. Clase strans legate intre ele. In momentul in care ajungem sa avem o colectie de clase care sunt strans legate intre ele sistemul devine monolit. Orice modificare ajunge sa fie extrem de greu de facut si necesita cunoasterea foarte buna a sistemului.
  7. Imposibilitatea de a modifica anumite clase. Uneori avem nevoie sa modificam clase la care nu avem acces la codul sursa sau necesita modificarea unui numar mare de subclase. Pentru a evita acest lucru putem sa folosim Adapter sau Visitator pattern.
  8. Dependinte directa fata de un obiect sau o implementare. Este reprezentat in cazul in care o clasa conoaste modul in care o alta clasa functioneaza si este implementat. Modificarea aceste clase poate sa cauzeze modificari in cascada la toate clasele care folosesc clasa respectiva.
http://en.wikipedia.org/wiki/Design_pattern#Gang_of_Four

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