Circle the letter of the best answer. For each starred (*) question, explain your answer or show your work. Answer all 10 questions.
- Which of the following is always private?
a. constructor b. instance variables
c. setters d. to_s method
- Which symbol is used in Windows and Unix to redirect STDOUT to a file?
a. > b. < c. << d. 2>
- Which method is automatically called when a class object is printed with the print method?
a. new b. super c. to_i d. to_s
- *What is the output of this print statement? Explain your answer or show your work.
print “2” * 3, “n”
a. 222 b. 33 c. 6
d. An error message is written to STDERR.
- *After these assignment statements
x = 5.64
y = “inches”
Which of these print statements is correct? Explain your answer or show your work.
a. print x + y, “n” b. print x.to_i + y, “n”
c. print x, y, ‘n’ d. print “%5.2f %sn” % [x, y]
- *What is output? Explain your answer or show your work.
x = 43
y = 109
print “%08b %02x %d” % [x & y, x | y, x ^ y]
a. 01000110 29 70 b. 00101001 6f 70
c. 00101001 6f 70 d. 01101111 6f 41
- *What is output? Explain your answer or show your work.
“[email protected]#”.each_byte do |c|
print “%02x” % [c]
end
a. 212223 b. 214023 c. 336435 d. 336699
- *What is the output? Explain your answer or show your work.
n = 38
i = 9
while i < 100
print n <=> i
i *= 3
end
a. -1-11 b. 11-1 c. 92781 d. truetruefalse
- *Which of these methods swaps the top two elements of the input array? (The two top elements are the elements with the highest indices.) Explain your answer or show your work.
a. def swap(input) b. def swap(input)
s = input.pop s = input.pop
t = input.pop t = input.pop
input.push(s) input.push(t)
input.push(t) input.push(s)
end endc. def swap(input) d. def swap(input)
s = input.shift t = input.shift
t = input.pop s = input.shift
input.push(s) input.unshift(t)
input.push(g) input.unshift(s)
end end
- Which test is used to check if inheritance makes sense?
a. is-a b. has-a c. substitution d. collection
Part B: Predict the Output.
Predict the output by performing a hand variable trace. For problems 1, 2, and 3, the output is worth 20% of the credit; the explanation of how you obtained your output is worth 80%. In each case, you may check your answer by running the Ruby script.
Predict the output and explain how you obtained the answer:
def f(n)
(2..n).each do |m|
if n % m == 0
return m
end
end
end
print f(35)
Part C
The Car and SportsCar objects both drive on a straight-line track of unlimited length. The only difference between Car and SportsCar objects is that a sportscar has greater acceleration and maximum speed. Predict the output and explain how you obtained your answer:
== File: Car.rb ==========================
class Car
attr_reader :vin, :color, :location,
:speed, :max_speed, :acceleration
def initialize(the_vin, the_color)
@vin = the_vin
@color = the_color
@location = 0
@speed = 0
@max_speed = 100
@acceleration = 10
end
def press_accelerator
if @speed < @max_speed
@speed += @acceleration
end
end
def press_brake
if @speed > 0
@speed -= 20
end
end
def drive(the_time)
@location += @speed * the_time
end
def to_s
return “car: Color=#{@color}, VIN=#{@vin}”
end
end
== File: SportsCar.rb ====================
require ‘./Car’
class SportsCar < Car
def initialize(the_vin, the_color)
super(the_vin, the_color)
@max_speed = 200
@acceleration = 20
end
def to_s
return “sports” + super
end
end
== File: Test.rb =============
require ‘./Car’
require ‘./SportsCar’
c1 = Car.new(‘1G6AF5SX6D0125409’, ‘silver’)
print c1, “n”
(1..5).each do |i|
c1.press_accelerator
end
c1.drive(60)
(1..3).each do |i|
c1.press_brake
end
c1.drive(60)
print “c1 location: “, c1.location, “n”
c2 = Car.new(‘2H7BG5TY2E0243862’, ‘red’)
print c2, “n”
(1..5).each do |i|
c2.press_accelerator
end
c2.drive(60)
(1..3).each do |i|
c2.press_brake
end
c2.drive(60)
print “c2 location: “, c2.location, “n”
==========================================
Part D: Find the Errors.
Find the errors in the following class and test script. There are about 5 errors in each class.
== File: CelestialObject.rb ==========================
class Celestial_Object
def initialize(the_name)
@name = the_name
end
def name
return @name
end
def name<-(the_name)
@name = the_name
def toString
return “Name of Celestial Object: %s % name
end
end
== File: Planet.rb ===================================
require ‘CelestialObject’
class Planet > CelestialObject
attr_accessor :day, year
def initialize(the_name, the_day, the_year)
super(the_name)
@day = the_day
@year = the_year
end
def to_s
return super + “n” +
(“Length of Day: %dnLength of Year: %d” %
@day, @year)
end
end
== File: Star.rb =====================================
require ‘./CelestialObject’
class Star < CelestialObject
attr-accessor :declination, :r_ascension, :magnitude
def initialize(the_name, the_dec, the_asc, the_mag)
super(the_name)
@declination = the_dec
@r_ascension = the_asc
@magnitude = the_mag
end
def to_s
return super + “n” +
(“Declination: %sn” +
“Right Ascension: %sn” +
“Magnitude: %6.2f”) %
[@declination, @r_ascension; magnitude]
end
== File: Test.rb =====================================
require ‘./Planet’
require ‘./Star’
p1 = Planet.initialize(“Mars’, 24.7, 687.0)
print p1, “nn”
s1 = Star.new(“Spica:”, %Q=-11deg 9′ 41″/,
“13h 25m 12s, 0.98)
print s1, ‘n’
======================================================
Part E: Write a Standalone Method and a Unit Test Class
- Write a standalone method named count_letters that returns the number of occurrences of a specified letter lines in an input string.
Running this test code should produce the output shown:
state = %Q/mississippi/
print count_letters(state, “i”), “n”
print count_letters(state, “p”), “n”
print count_letters(state, “w”), “n”
# Output:
4
2
0
- Write a unit test class that tests the count_letters method. Either use this Unit Test Template for your test class or create a Minitest test class as shown in the 1/12 Lecture Notes.
==== Unit Test Template =======================
require './class-name.rb'
require 'test/unit'
class TestClass < Test::Unit::TestCase
def test1
assert_equal expected_value, computed_value
end
end
======= Minitest ==================================
require ‘minitest/autorun’
require ‘./method-defs.rb’
class TestMethods < MiniTest::Unit::TestCase
def test1
assert_equal ‘p’, first_char(‘peach’)
assert_equal ‘r’, first_char(‘peach’)
assert_equal ‘p’, first_char(”)
assert_equal nil, first_char(”)
end
end
0 comments