Midterm ExamExam Question DifficultyQuestion NatureEssay QuestionsUnderstanding CodeSlide 6Slide 7Slide 8Slide 9Writing CodeSlide 11Declarations Vs Statement OrderExpressions Vs StatementsPure Vs Impure FunctionsScopeSlide 16Identifier ScopeSlide 18Midterm Exam• 75 points• 1 min per point• Allocate time proportionate to points• Closed book• Chapters 1-5 (except char)• PDF/PS with index and corrections coming• Look at exercisesExam Question Difficulty• Obvious questions• Questions requiring studying• Challenging questionsQuestion Nature•Essay Questions•Understanding Code•Writing/Modifying CodeExample syntaxEssay Questions•Definitions–Define class.•Distinction–Distinguish Expression from Statement.•Rationale–Why style principles?•Comparison–Pros and Cons of using Named Constants & Literals.Understanding Code•Identify Errors and Style Principle Violationsclass aMoneyconverter { int Cents (dollars) { return dollars*100; }}Understanding Code•Classify Components–properties, variables, signatures ….public class C () {public int m = 100;public int getD() {return m;} public void setD(int i) {m = i;}public int getC() {return m*100;}public int convert (int i) {return i*100;}` }Understanding Code•Evaluate Method Callspublic class C () {public int m = 100;public int getD() {return m;} public void setD(int i) {m = i;}public int getC() {return m*100;}public int convert (int i) {return i*100;}` }Understanding Code•Evaluate, Parenthesize, and Type ExpressionsExpression Type Value5 + 3 + 4 int 8Understanding Code•Parenthesize ExpressionsExpression Pa renthesized5 - 3 - 3 (5-3) - 3Writing Code•Improve Codepublic class C () {public int m = 100;public int getD() {return m;} public void setD(int i) {m = i;}public int getC() {return m*100;}public int convert (int i) {return i*100;}` }Writing Code•Write Expressions–i is 2–Answer: i == 2•Method–cube(x)•Class, Interface–Like assignmentsDeclarations Vs Statement Order•Order of variable and method declarations in a class does not matter in Java.•Order of statements in a method body matters.–Statements executed sequentially.Expressions Vs StatementsExpression: Piece of code yielding value•5•“setWeight called”•newHeight•x*x•weight/(height*height)Statement: computer instruction executed autonomously•System.out.println(“seWeight called”);•return x*x•bmi = weight/(height*height);Expression always evaluated as part of some statement.Pure Vs Impure FunctionsABMISpreadsheet InstancegetWeightweight Body accessescalculateBMI(77,1.77)calculateBMI(77,1.77) 24.5724.57getWeight()getWeight()setWeight(77)7771......setWeight(71)ABMICalculator InstancecalculateBMIweight Body accessesheightpublic class AnotherBMISpreadsheet implements BMISpreadsheet{double height, weight, bmi;public double getHeight() {return height;}public void setHeight(double newHeight) {height = newHeight;bmi = calculateBMI();}public double getWeight() {return weight;}public void setWeight(double newWeight) {weight = newWeight;bmi = calculateBMI();}public double getBMI() {return bmi;}double calculateBMI() {double heightInMetres = height*CMS_IN_INCH/100;return (weight/LBS_IN_KG) / (heightInMetres*heightInMetres);}}ScopeheightInMetres Scopeheight Scopeillegal Scopepublic class AnotherBMISpreadsheet implements BMISpreadsheet{double height, weight, bmi;public double getHeight() {return height;}...}ScopegetHeight() ScopeObjectEditorABMISpreadsheetIdentifier Scope•Region of code where the identifier is visible.•Arbitrary scopes not possible•Least Privilege => Make scope as small as possiblepublic cla ss AnotherBMISpreadsheet implements BMISpreadsheet{double height, weight, bmi;public void setHeight(double newHeight) {double height = heightInMetres;bmi = calculateBMI();}...final dou ble LBS_IN_KG = 2.2;final dou ble CMS_IN_INCH = 2.54;double calculateBMI() { dou ble heightInMetres = height*CMS_IN_INCH/100; return (weight/LBS_IN_KG) / (heightInMetres*heightInMetres) ;}}ScopeheightInMetres
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