Midterm Exam 2

1
Midterm Exam 2

• 75 points
• 1 min per point
• Allocate time proportionate to points
• Closed book
• Chapters 6-9
• Look at exercises

2
Exam Question Difficulty

• Obvious questions
• Questions requiring studying
• Challenging questions
• Hardness of exam proportional to hardness of
  assignments

3
Question Nature

• Essay Questions
• Understanding Code
• Writing/Modifying Code

4
Essay Questions

• Definitions
• Define class method.
• Distinction
• Distinguish class and instance methods.
• Rationale
• Why class methods?
• Comparison
• Pros and Cons of using Class and Instance Methods

5
Understanding Code

• Identify Errors
• Class Vs Interfaces as Types
• Static Vs instance methods/constants/variables
• Off-by-one errors
• Infinite loops
• Null pointers
• .

6
Understanding Code

• Identify Style Principle Violations
• Class as Types
• Instance methods/constants instead of class
  methods/constants
• Code duplication in If-Else
• No separation of Concerns
• Side Effects
• ...

7
Understanding Code

• Identify Errors Style Violations
• public interface Money
• public int getPounds()
• public int getDollars()
• public int DOLLARS_IN_LB 1.8
• public class PoundMoney implements Money
• static int assets
• public static int getPounds()
• return assets
• public int getDollars()
• return assetsDOLLARS_IN_LB

8
Understanding Code

• Characterize Code
• Overloaded Polymorphic Methods
• Static Instance Variables
• Logical Physical Structure
• Counter Event-controlled loops
• Side Effects
• ...

9
Understanding Code

• Trace execution (explain output) of programs
  involving
• Conditionals
• Loops
• Class/instance variables
• Constructors
• main method

10
Understanding Code (example)

• What is the output of the following loops, when n
  is (i) 4 and (ii) 4.
• a)
• while (n gt 0)
• n n 1
• System.out.println (n)
• b)
• while (n ! 0)
• n n 1
• System.out.println (n)

11
Writing Code

• Improve Code by removing style principle
  violations. E.g
• public void fancyPrintGrade(int score)
• if (score lt PASS_CUTOFF true)
• System.out.println("FAILED")
• System.out.println("")
• System.out.println("")
• System.out.println("Need to take the course
  again.")
• else
• System.out.println("PASSED")
• System.out.println("")
• System.out.println("")
• System.out.println("Congratulations!")

12
Writing Code

• Write Functions/Procedures/Main Methods/Classes
  Involving
• Loops, Conditionals, Static Vars, ...
• E.g
• Write a program that prints all positive odd
  numbers less than some limit n.