| 6.1 |
hello from ClassA
hello from ClassB
method A from ClassB
|
| 6.2 |
hello from ClassA
hello from ClassB
hello from ClassC
method A from ClassB
method A from ClassC
|
| 6.3 |
hello from ClassA
hello from ClassB
hello from ClassC
method B from ClassC
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| 6.4 |
a) Polygon has 13 sides
b) Hexagon has 6 sides
c) Polygon has 6 sides
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| 6.5 |
As seen in Exercise 4, the fact that a class and all its subclasses share the value for a class
variable means we may change the value of a class variable even when we do not intend do. In the Polygon class,
we initially had the number of sides for a polygon stored in the class variable numSides to have a value of 12.
In the Hexagon class, we access numSides and change the value to 6. The value of numSides is now set to 6 even for Polygon objects.
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| 6.6 |
“eval false; 3” “eval true; nil”
|
| 6.7 |
class Integer
def fib
if self < 1 return
num1 = 0
num2 = 1
(self -1).times do
temp = num1 + num2
num1 = num2
num2 = temp
end
num1
end
end
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| 6.8 |
Open ended. Solutions will vary.
|
| 6.9 |
for num in (1..50)
num.fib.isEven?
end
|
| 6.10 |
The problem is in line 9 of the Airplane class. The object variable @flightNum stores an Integer value and in line 9, we attempt to add this Integer value to the String "Flight Number ==>". A String and an Integer are unmixable data types and we are not allowed to add them directly. In order to correct this, we must first convert the value in @flightNum to a String. To correct the error, line 9 should look like this:
puts "Flight Number ==>" + @flightNum.to_s
|
| 6.11 |
The way the current class is set up, we are not allowed to access the @flightNum object variable outside the Airplane class. In order to fix this error, we must add the following line of code to the class:
attr_accessor:flightNum
|
| 6.12 |
class Integer
def fact
if self<1
return end
product=self
x=self
(self-1).times do
product = product * (x-1)
x = x-1
end #end loop
puts product
end #end fact methodend
#end class
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| 6.13 |
class Slope
def initialize (x1, y1, x2, y2)
@x1 = x1
@y1 = y1
@x2 = x2
@y2 = y2
@slope = (y1-y2)/(x1-x2)
puts "The slope is " + @slope.to_s
end
end
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| 6.14 |
class String
def invert
newstring = String.new()
self.each_char() {|letter|
newstring = letter + newstring
}
return newstring
end
end
|
| 6.15 |
1 class Ball
2 def initialize (color, size, texture)
3 @attribute1 = color
4 @attribute2 = size
5 @attribute3 = texture
6 end
7 def display
8 puts "The Ball is: " + @attribute1 + “, " + @attribute2 + “, " + @attribute3
9 end
10 end
1 require 'Ball'
2 newBall = Ball.new(‘green’, ‘small’, ‘bouncy’)
3 newBall.display
|
| 6.16 |
class Number_comparison
def initialize (num1, num2)
@num1 = num1
@num2 = num2
if @num1 > @num2
puts @num1.to_s + " is the larger number."
else
if @num1 < @num2
puts @num2.to_s + " is the larger number."
else
puts "The numbers are equal."
end
end
end
end
|
| 6.17 |
class String_comparison
def initialize (string1, string2)
@string1 = string1
@string2 = string2
if @string1.length == @string2.length
puts "The strings have the same length."
else
puts "The strings do not have the same length."
end
end
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| 6.18 |
Need to set object variables.
|
| 6.19 |
Solution: For part a, for example –
|
| 6.20 |
class Inv_number < Inventory
def initialize(item, maker, number)
super
@number=number #stored as integer
end
def display
super.display
puts "Number ==>" + @number.to_s
end
end
newInv = Inventory.new("computer", "IBM")
newInvNum = Inv_number.new("computer", "IBM", 15)
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| 6.21 |
The class will not be able to access the attributes and methods that are defined in the superclass. This will negate the whole point of inheritance.
|
| 6.22 |
Class: Ball (radius, color, texture)
Instance1: Bowling ball – 5 inch, black, hard.
Instance2: Tennis ball – 1.5 inch, green, felt.
Subclass: Basketball (radius, color, texture, indoor/outdoor, level)
Instance1: Child’s basketball – 4 inch, orange, rubber, outdoor, child.
Instance2: NBA basketball – 5.5 inch, brown, leather, indoor, NBA.
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