AP Computer Science A

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1 2018 AP Cmputer Science A Sample Student Respnses and Scring Cmmentary Inside: Free Respnse Questin 3 RR Scring Guideline RR Student Samples RR Scring Cmmentary 2018 The Cllege Bard. Cllege Bard, Advanced Placement Prgram, AP, AP Central, and the acrn lg are registered trademarks f the Cllege Bard. Visit the Cllege Bard n the Web: AP Central is the fficial nline hme fr the AP Prgram: apcentral.cllegebard.rg

2 2018 SCORING GUIDELINES Apply the questin assessment rubric first, which always takes precedence. Penalty pints can nly be deducted in a part f the questin that has earned credit via the questin rubric. N part f a questin (a, b, c) may have a negative pint ttal. A given penalty can be assessed nly nce fr a questin, even if it ccurs multiple times r in multiple parts f that questin. A maximum f 3 penalty pints may be assessed per questin. 1-Pint Penalty v) Array/cllectin access cnfusin ([] get) w) Extraneus cde that causes side-effect (e.g., printing t utput, incrrect precnditin check) x) Lcal variables used but nne declared y) Destructin f persistent data (e.g., changing value referenced by parameter) z) Vid methd r cnstructr that returns a value N Penalty Extraneus cde with n side-effect (e.g., valid precnditin check, n-p) Spelling/case discrepancies where there is n ambiguity* Lcal variable nt declared prvided ther variables are declared in sme part private r public qualifier n a lcal variable Missing public qualifier n class r cnstructr header Keywrd used as an identifier Cmmn mathematical symbls used fr peratrs ( < > <> ) [] vs. () vs. <> = instead f == and vice versa length/size cnfusin fr array, String, List, r ArrayList; with r withut ( ) Extraneus [] when referencing entire array [i,j] instead f [i][j] Extraneus size in array declaratin, e.g., int[size] nums = new int[size]; Missing ; where structure clearly cnveys intent Missing { } where indentatin clearly cnveys intent Missing ( ) n parameter-less methd r cnstructr invcatins Missing ( ) arund if r while cnditins *Spelling and case discrepancies fr identifiers fall under the N Penalty categry nly if the crrectin can be unambiguusly inferred frm cntext, fr example, ArayList instead f ArrayList. As a cunterexample, nte that if the cde declares int G=99, g=0;, then uses while (G < 10) instead f while (g < 10), the cntext des nt allw fr the reader t assume the use f the lwer case variable The Cllege Bard. Visit the Cllege Bard n the Web:

3 2018 SCORING GUIDELINES Questin 3: Cde Wrd Checker Class: CdeWrdChecker 9 pints Intent: Define implementatin f a class t determine if a string meets a set f criteria +1 Declares header: public class CdeWrdChecker implements StringChecker +1 Declares all apprpriate private instance variables +3 Cnstructrs +1 Declares headers: public CdeWrdChecker(int, int, String ) and public CdeWrdChecker(String ) +1 Uses all parameters t initialize instance variables in 3-parameter cnstructr +1 Uses parameter and default values t initialize instance variables in 1-parameter cnstructr +4 isvalid methd +1 Declares header: public blean isvalid(string ) +1 Checks fr length between min and max inclusive +1 Checks fr unwanted string +1 Returns true if length is between min and max and des nt cntain the unwanted string, false therwise 2018 The Cllege Bard. Visit the Cllege Bard n the Web:

4 2018 SCORING GUIDELINES Questin 3: Scring Ntes Class CdeWrdChecker Pints Rubric Criteria Respnses earn the pint if they... Declares header: public class +1 CdeWrdChecker implements StringChecker Declares all apprpriate +1 private instance variables +3 Cnstructrs Declares headers: public CdeWrdChecker (int, int, +1 String ) and public CdeWrdChecker (String ) Uses all parameters t initialize instance +1 variables in 3- parameter cnstructr Uses parameter and default values t +1 initialize instance variables in 1- parameter cnstructr +4 isvalid methd Declares header: public blean +1 isvalid (String ) Checks fr length +1 between min and max inclusive Checks fr unwanted +1 string Returns true if length is between min and max +1 and des nt cntain the unwanted string, false therwise 9 pints Respnses will nt earn the pint if they... mit keywrd public declare class private declare class static declare variables as static mit keywrd private declare variables utside the class mit keywrd public declare methd static declare methd private initialize instance variables t default values when declared have incrrect checks fr length and/r cntainment, but return the crrect value based n thse checks fail t declare instance variables initialize lcal variables instead f instance variables assign variables t parameters fail t declare instance variables initialize lcal variables instead f instance variables assign variables t parameters fail t declare methd public declare methd static fail t use instance variables fail t declare the methd header fail t use instance variables fail t declare the methd header fail t declare the methd header fail t return in all cases nly check ne substring lcatin fr cntainment 2018 The Cllege Bard. Visit the Cllege Bard n the Web:

5 2018 SCORING GUIDELINES Questin 3: Cde Wrd Checker public class CdeWrdChecker implements StringChecker { private int minlength; private int maxlength; private String ntallwed; } public CdeWrdChecker(int minlen, int maxlen, String symbl) { minlength = minlen; maxlength = maxlen; ntallwed = symbl; } public CdeWrdChecker(String symbl) { minlength = 6; maxlength = 20; ntallwed = symbl; } public blean isvalid(string str) { return str.length() >= minlength && str.length() <= maxlength && str.indexof(ntallwed) == -1; } These cannical slutins serve an expsitry rle, depicting general appraches t slutin. Each reflects nly ne instance frm the infinite set f valid slutins. The slutins are presented in a cding style chsen t enhance readability and facilitate understanding The Cllege Bard. Visit the Cllege Bard n the Web:

6 3A Write the cmplete CdeWrdChecker class. Yur implementatin must meet all specificatins and cnfrm t all examples. pvt1 cl.,)) {Je vj,.\c1e,r,., '"'f'f"'"ls Slrr:y ckt.yer f pri'tei i11f ""'11; pr,vt1i't,\--t vt--1 ii rri1-ie t,(',.,,, rj; f Jt C,k 1,,1,1) Cl,,, Y 0.+ ";,-d b, S'f 1 c) Vlilll:. q v l-z ; b.,,d c. p:\ll c.j!,/,,j Ck, V,, ( <J,9 / V'I\[-::: Gi, l[.,ll -:. i,(). "' "' d.., ;.. be,, le,a > V,\d ( ').) d,) j ) /I; if ( d r, -fl-() 4> v,/1 tr.ie.5/l () :,-.,,J Y {,f,/,,,, f v. / H v J 2 } re tvr(l :fi -e i if ( sir,,je,,of {w11) :> 0} { rel,,.. 0 il e. Unauthrized cpying r reuse f any part f this page la Illegal GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

7 Write the cmplete CdeWrdChecker class. Yur implementatin must meet all specificatins and cnfrm t all examples. f w hc... fk WuJ... (;.,r """) ) }- f,1ivy ) S-J j ii\\/ ) fl.:s.,.,:,... {11 ),i./1. ('vi -:,, :I\ I\";.µ,.... ('/lb.., ;r ( sh-, h -, J {.),. f',"6:>t Qg rqlvll,k>1>-.t. ; / ; 7 Unauthrlied cpying r reuse f any part f this pag la Illegal. s>rtf,.,-/1-15- GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

8 Write the cmplete CdeWrdChecker class. Yur implementatin must meet all specificatins and cnfrm t all examples. \J \J\.,\i._ { (\ r)..\. \/ '' :. '., J ( \ '\ <',. l. t ( ( i:_ r.. >....., -:1 / fl. 1 1 t 1 /\..c,l r' I 't. ' ) ; fl " ; \) 0 l.,l, '- \.,i:>c,\ e 6\-1" I':., \J \i LG( ( 1 6 ra f ) {_ '\..\'-.l1,l,.l,1,, l l) L. t'\ \ ( t. 1\ f, \,...\.,;_ C j 0 \f\ \\ t -;,.l.\, ( -1/,l..l)':>t->,./t',) ' : C) ) I,. I. {{l,lc. l,;1...l f-(.) ',\".1'1.tJ J \-'v \ ) [. \ \- ( S \, - -:., ' I, i O l t ), "' ",+-.,,, f" ) )., '!/ I', Al,I \'\.'._1...,,r-.\,.\,,, Unauthrized cpying r reuse f any part f thl page Is Illegal. GO ON TO THE NEXT PAGE The Cllege Bard. Visit the Cllege Bard n the Web:

9 2018 SCORING COMMENTARY Questin 3 Overview This questin tested the student's ability t: Write prgram cde t define a new type by creating a class; Write prgram cde t create bjects f a class and call methds; and Write prgram cde t satisfy methds using expressins, cnditinal statements, and iterative statements. Students were asked t design the class CdeWrdChecker s that it implements the methd isvalid in the given interface, StringChecker. In additin t demnstrating an understanding f class cnstructrs and methd header syntax, students had t crrectly declare, initialize, access, and update instance variables. Students were expected t prperly encapsulate their data members by declaring them as private and t prperly define the interface methd isvalid and expse it by declaring the methd public. Students als had t recgnize that tw cnstructrs needed t be included in rder t cnfrm t the examples given. This questin primarily addressed the fundamental skill f hw t create a class s that it adheres t a specific interface. Hwever, there was als a lgic cmpnent required t make the class peratinal. The students had t demnstrate an understanding f hw t cntrl the visibility f class elements s that the language wuld enfrce the separatin. The internal representatin had t be hidden and inaccessible frm the client, and the interface methd had t be defined and made publicly available. Implementing the isvalid methd required students t find the length f a string and check if it was within a specified range and als t determine if ne string was a substring f anther. Students then needed t return an apprpriate Blean value based n the result f their lgic. Sample: 3A Scre: 8 In this slutin pint 1 was earned because the header is crrectly declared. Pint 2 was earned because all apprpriate private instance variables are declared. Pint 3 was earned because the 3-parameter cnstructr and the 1-parameter cnstructr headers are declared. Pint 4 was earned because each f the parameters is used t initialize the instance variables. Pint 5 was earned because the instance variables fr minimum and maximum cde length are initialized t 6 and 20, respectively, and the String parameter is used t initialize the String instance variable. In the slutin fr the isvalid methd, pint 6 was earned because the header is crrectly declared. Pint 7 was earned because the length f the String parameter is crrectly cmpared t the minimum and maximum lengths. Pint 8 was nt earned because the value returned by the indexof methd is checked using > 0 rather than > 0. Pint 9 was earned because the cnditinal statement returns false when given an invalid length, false when the instance variable is fund in the String parameter, and true therwise. Sample: 3B Scre: 6 In this slutin pint 1 was nt earned because the header uses extends StringChecker. Pint 2 was earned because all apprpriate private instance variables are declared. Pint 3 was nt earned because the respnse fails t declare the 1-parameter cnstructr. Pint 4 was earned because each f the parameters is used t initialize the instance variables. Pint 5 was nt earned because the respnse fails t implement the 2018 The Cllege Bard. Visit the Cllege Bard n the Web:

10 2018 SCORING COMMENTARY Questin 3 (cntinued) 1-parameter cnstructr. In the slutin fr the isvalid methd, pint 6 was earned because the header is crrectly declared. Pint 7 was earned because the length f the String parameter is determined t be between the minimum and maximum lengths, inclusive. Pint 8 was earned because the respnse checks fr the unwanted string by calling the indexof methd and cmparing it t -1. Pint 9 was earned because the cnditinal statement returns false when given an invalid length, false when the instance variable is fund in the String parameter, and true therwise. Sample: 3C Scre: 2 In this slutin pint 1 was nt earned because the header incrrectly includes parameters. Pint 2 was nt earned because n private instance variables are declared. Nt declaring instance variables als resulted in the lss f pints 4, 5, 7, and 8. Pint 3 was nt earned because the respnse fails t declare the 1-parameter cnstructr. Pint 4 culd have been earned if instance variables had been declared. In the slutin fr the isvalid methd, pint 6 was earned because the header is crrectly declared. Pint 7 culd have been earned because the length f the String parameter is cmpared t the minimum and maximum lengths. Pint 8 was nt earned because the instance variables are nt declared. In additin, the pint wuld nt have been earned because the respnse, while traversing the String parameter ne index at a time, fails t test the last ccurrence f the substring. Pint 9 was earned because the lgic fr finding an invalid cde wrd is crrect The Cllege Bard. Visit the Cllege Bard n the Web:

AP Computer Science A

AP Computer Science A 2018 AP Cmputer Science A Sample Student Respnses and Scring Cmmentary Inside: Free Respnse Questin 1 RR Scring Guideline RR Student Samples RR Scring Cmmentary 2018 The Cllege Bard. Cllege Bard, Advanced