Introduction to Computer Science, Shimon Schocken, IDC Herzliya. Lecture A very small selection of some topics in Object-Oriented Design

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1 Introduction to Computer Science, Shimon Schocken, IDC Herzliy Lecture 11.1 A very smll selection of some topics in Object-Oriented Desin OO Desin, Shimon Schocken IDC Herzliy, slide 1 Systems development The development of ny softwre system involves severl stes: Ech one of these stes is bsed on sinicnt body of knowlede nd prctice Requirements nlysis: Dt Processes Desin Implementtion Testin Deployment Mennce Introduced in course Systems development is not computer science. It s discipline tht ersects CS, mnement science, opertions reserch, systems nlysis, nd enineerin. How cn you lern systems development? Other courses in CS / IT / mnement prorms On-the-job workshops Hnds-on eperience Common sense. OO Desin, Shimon Schocken IDC Herzliy, slide 2

2 Testin How cn we ensure tht (lre-scle) prorm does wht it s supposed to do? Correctness proof (rnes from the imprcticl to the impossible) Testin: Unit-testin Desinin testin Test plnnin Reression testin Test suite: well-documented collection of test-cses, ech describin prticulr input, user ction, etc., nd desired output or outcome OO Desin, Shimon Schocken IDC Herzliy, slide 3 Blck-bo testin Uses the system s API only Inputs re seprted o equivlence cteories The borders of the cteory must be crefully tested, to ctch one off errors Emple (tken from some API): Returns Returns true true is is in in the the rne rne 0 0 to to 99, 99, inclusive inclusive boolen boolen iscent( iscent( The test suite of method should be somethin like: -500, -1, 0, 1, 50, 98, 99, 100, 500. OO Desin, Shimon Schocken IDC Herzliy, slide 4

3 White-bo testin Anlyzes the code itself by tryin to visit every possible pth tht the prorm flow my tke ( sttement covere ) Used to ensure correctness nd prevent hckin Softwre testin is bi business: Softwre tools Best prctices Consultin compnies 4 million hits on Goolin softwre testin OO Desin, Shimon Schocken IDC Herzliy, slide 5 Systems development The development of ny softwre system involves severl stes: Requirements nlysis: Dt Processes Desin OO Implementtion Testin Deployment Mennce OO Desin, Shimon Schocken IDC Herzliy, slide 6

4 OO Desin: reltionships How do I model n Amzon-like system? OO Desin Products s Books Trnsctions Etc. When we identy es (prt of system desin), we typiclly try to mp the es on eistin desin ptterns. The OO literture describes dozens of such desin ptterns, nd OO desiners re well dvised to consult them Typiclly, the es tht we will end up identyin nd documentin re relted to ech other in three bsic wys: Dependency: C1 uses C2. Emple: Trnsctions uses Products Aretion: C1 hs- C2. Emple: s hs- Inheritnce: C1 is- C2. Emple: Book is- Product OO Desin, Shimon Schocken IDC Herzliy, slide 7 Dependency When C1 uses the services of C2 is some wy, we sy tht C1 uses C2 or C1 depends on C2. Emples: C1 uses C2 Clss C Mth.sqrt(y) Mth.sqrt(y) The cll to the method cretes C uses Mth dependency. This dependency is so bsic tht we don t bother to note it Clss C (file.isdirectory()) (file.isdirectory()) The file object ws either creted by C or pssed to one of its methods s prmeter. Either wy cretes C uses File dependency Clss C ct1.trnsferto(400,ct) ct1.trnsferto(400,ct) Sme s in previous cse: C uses BnkAccount dependency Clss Set.insertSet(s2).insertSet(s2) One object erctin with nother object from the sme, cretin Set uses Set dependency. OO Desin, Shimon Schocken IDC Herzliy, slide 8

5 Dependency emple customer uses firstnme, firstnme, lstnme; lstnme; The cn be home, home, shippin; shippin; used by other es, customer customer simplyin their definitions. ( ( firstnme, firstnme, lstnme, lstnme, home, home, n n ddress ddress shippin) shippin).firstnme.firstnme firstnme; firstnme; street, street, city; city;.lstnme.lstnme lstnme; lstnme; lon lon.home.home home; home;.shippin.shippin shippin; shippin; n n ddress ddress ( ( street, street, city, city, A A tetul tetul rep. rep. of of customer. lon customer. lon zipcode) zipcode) to() to().street.street street; street; ;.city ;.city city; city; firstnme firstnme.zipcode.zipcode lstnme lstnme \n; \n; home home :\n :\n home home \n; \n; Returns Returns ddress ddress s s tet tet Shippin Shippin :\n :\n to() to() shippin; shippin; street street \n \n ; ; city city,, OO Desin, Shimon Schocken IDC Herzliy, slide 9 Aretion If n object of C1 is some collection of objects of C2, we sy tht C1 retes C2, or C1 hs- C2 C1 hs- retes C2 OO Desin, Shimon Schocken IDC Herzliy, slide 10

6 Aretion emple s s min min ([] ([] rs) rs) home; home; shippin shippin (10E (10E 14th 14th Street, Street, New New York, York, 20010); 20010); [] [] customers customers [2]; [2]; In In relity relity the the rry rry will will be be bier bier home home (15 (15 Dekel Dekel Street, Street, Rnn, Rnn, 24551); 24551); customers[0] customers[0] (Ron, (Ron, Tmir, Tmir, home, home, shippin); shippin); home home (10 (10 Neev Neev Street, Street, Beer Beer Shev, Shev, 44132); 44132); customers[1] customers[1] (Michl, (Michl, Shmir, Shmir, home, home, shippin); shippin); ( ( i0 i0 ; ; i i customers.lenth customers.lenth ; ; i) i) System.out.prln System.out.prln (customers[i]); (customers[i]); System.out.prln System.out.prln (); (); Aretion reltionship: s retes customer OO Desin, Shimon Schocken IDC Herzliy, slide 11 UML dirm uses s min (rs : []) : retes - firstnme : - lstnme : - home : - shippin : uses - street : -city: - zipcode : lon to() : to() : Unied Modelin Lnue (UML): populr rphicl nottion OO desin Useful tool visulizin the desin of comple softwre rchitectures UML is Lnue independent Ech is represented by block with three elements: nme, ttributes, opertions Reltionships between es re reprtesented by rrows. OO Desin, Shimon Schocken IDC Herzliy, slide 12

7 Outline Systems development Testin Clss reltionships Dependency Aretion Inheritnce Interfces Modulrity Enumrted types revisited OO Desin, Shimon Schocken IDC Herzliy, slide 13 Interfce musicl musicl instrument instrument erfce erfce ; ; ; ; We wish to crete severl es, ech representin musicl instrument We wnt to ce ll these es to set of behviors tht every musicl instrument must hve This desin ol cn be chieved usin n erfce An erfce sys: This is wht es tht prticulr erfce should look like Ech tht n erfce sys: I conm to the erfce tht I. Public Public Guitr Guitr Guitr Guitr (...) (...) Vrious Vrious methods methods Code Code tht tht plys plys Code Code tht tht mutes mutes Flute Flute Similr, Similr, must must nd nd Flute Flute Similr, Similr, must must nd nd OO Desin, Shimon Schocken IDC Herzliy, slide 14

8 Interfce: the rules of the me The erfce: Interfce collection of constnts nd bstrct methods An erfce file is complition unit, just like files An erfce cnnot be instntited (no ) All the methods of n erfce re, by defult, nd bstrct musicl musicl instrument instrument erfce erfce ; ; ; ; Guitr Guitr Must Must nd nd The in : A cn 0, 1, or more erfces The impelemtin must provide tions ll the methods mentioned in ll the erfces it is in; filure to do so cuses compiltion error Multiple es cn the sme erfce. The Jv stndrd librry includes mny erfces. OO Desin, Shimon Schocken IDC Herzliy, slide 15 Emple: the Comprble erfce Prt of the jv.ln pcke Includes sinle bstrct method: compreto() Implemented by numerous es, includin word1 word1 scn.netline(); word2 word2 scn.netline(); (s1.compreto(s2) 0) 0) System.out.prln ( word1 ( word1 preceded preceded word2 ); word2 ); Interfce Comprble API This erfce imposes totl orderin on the objects of ech tht it. This orderin is referred to s the 's nturl orderin, nd the 's compreto method is referred to s its nturl comprison method. Lists nd rrys of objects tht erfce cn be sorted utomticlly by Collections.sort (nd Arrys.sort). Objects tht erfce cn be used s keys in sorted mp or elements in sorted set, without the need to specy comprtor compreto(object o) Prmeters: o - the Object to be compred. Returns: netive eer, zero, or positive eer s object is less thn, equl to, or reter thn the specied object. Throws: ClssCstEception - the specied object's type prevents it from bein compred to Object. OO Desin, Shimon Schocken IDC Herzliy, slide 16

9 Emple: the Itertor erfce Prt of the jv.util pcke Describes stndrd wy to move throuh collection of objects, one object t time Implemented by mny itertor es in Jv OO Desin, Shimon Schocken IDC Herzliy, slide 17 Outline Systems development Testin Clss reltionships Dependency Aretion Inheritnce Interfces Modulrity Enumrted types revisited OO Desin, Shimon Schocken IDC Herzliy, slide 18

10 End comment: Modulrity Perhps the most importnt feture of well desined systems The best wy to tme compleity is to divide the system o smll, well-defined, mneble, unit-tested modules A modulr desin lso implies sovereinty: ech module should mne its own functionlity We will now see n emple tht Illustrtes modulr desin Revisits Jv s enumerted type concept. OO Desin, Shimon Schocken IDC Herzliy, slide 19 Enumerted types revisited Demo Demo enum enum ood, ood, pss, pss, fil; fil; min min ([] ([] rs) rs) 63; 63; null; null; > > 90) 90).ood;.ood; ( ( > > 60) 60) && && 90)) 90)).pss;.pss; 60) 60).fil;.fil; System.out.prln System.out.prln is: is: ); ); Modulr desin: the rde loic should idelly be deleted to stnd-lone. The hidden le of enum: is (behind the scene).hih,.pss,.fil re instnces of the More precisely, they re references to objects stored in vribles within the Since n enum is, we cn etend its definition t will. OO Desin, Shimon Schocken IDC Herzliy, slide 20

11 Enumerted types revisited, Tke 2 enum enum ood ood (90, (90, 100), 100), pss pss (75, (75, 89), 89), fil fil (64, (64, 74); 74); hih; hih; ( ( low, low, hih) hih).low.low.hih.hih hih; hih; etlow() etlow() ethih() ethih() hih; hih; Demo Demo min min ([] ([] rs) rs) ( ( : :.vlues()).vlues()) System.out.prln System.out.prln ( ( \t \t.etlow().etlow() \t \t.ethih());.ethih()); System.out.prln(78 System.out.prln(78 in in verbl verbl rde: rde:.toverbl(78));.toverbl(78)); Boolen Boolen withinrne withinrne ( ( ( ( > > low) low) && && hih)); hih)); toverbl toverbl ( ( ( ( : :.vlues()).vlues()) (.withinrne)) (.withinrne)) ; ; null; null; OO Desin, Shimon Schocken IDC Herzliy, slide 21