Group 3

Homeworks/Answer.md

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+# Feature Envy
+
+#BAD
+
+class Rectangle
+  attr_reader :width, :height
+  def initialize width = nil, height = nil
+    @width = width
+    @height = height
+  end
+end
+
+rect = Rectangle.new 2, 3
+perimeter = rect.width * rect.height
+
+
+#GOOD
+
+class Rectangle
+  def initialize width = nil, height = nil
+    @width = width
+    @height = height
+  end
+
+  def perimeter
+    @width * @height
+  end
+end
+
+
+rect = Rectangle.new 2, 3
+perimeter = rect.perimeter
+
+
+
+
+# Message Chains
+
+class Rectangle
+  def initialize width = nil, height = nil
+    @width = width
+    @height = height
+  end
+
+  def perimeter
+    @width * @height
+  end
+end
+
+#BAD
+rect = Rectangle.new 2, 3
+rect.perimeter.blank?
+
+
+# GOOD
+
+class Rectangle
+  def initialize width = nil, height = nil
+    @width = width
+    @height = height
+  end
+
+  def perimeter
+    @width * @height
+  end
+
+  def perimerter_blank?
+    perimeter.blank?
+  end
+end
+
+rect.perimerter_blank?
+
+
+#Large class
+
+#BAD
+
+class staff
+  def initialize staff_name, position, company_address, company_name
+    @staff_name = staff_name
+    @position = position
+    @company_name = company_name
+    @company_address = company_address
+  end
+
+  def infomation_staff
+    @staff_name + "," + @position
+  end
+
+  def infomation_company
+    @company_name + "," + company_address
+  end
+end
+
+#GOOD (Use Extract Class)
+
+class staff
+  def initialize staff_name, position
+    @staff_name = staff_name
+    @position = position
+  end
+
+  def infomation_staff
+    @staff_name + "," + @position
+  end
+end
+
+class company
+  def initialize company_address, company_name
+    @company_name = company_name
+    @company_address = company_address
+  end
+
+  def infomation_company
+    @company_name + "," + company_address
+  end
+end
+
+
+#Long parameter list
+#BAD
+
+class student_life
+  attr_accessor :exam_point, :frequent_point, :cc_point
+
+  def back_to_school
+    final_point = @exam_point * 0.7 + @cc_point * 0.2 + @frequent_point * 0.1
+    if exam_point < 4
+      puts "You win"
+    else
+      if final_point < 4
+        puts "You win"
+      else
+        puts "You lose"
+      end
+    end
+  end
+end
+
+
+#GOOD
+
+class student_life
+  attr_accessor :exam_point, :frequent_point, :cc_point
+
+  def calculate_final_point
+    @exam_point * 0.7 + @cc_point * 0.2 + @frequent_point * 0.1
+  end
+
+  def back_to_school
+    if @exam_point < 4 || calculate_final_point < 4
+      puts "You win"
+    else
+      puts "You lose"
+    end
+  end
+end
+
+
+# Switch-statements
+# Bad
+
+class Area
+   attr_accessor :name, :a 
+
+   def initialize
+     @name = name
+     @a = a
+   end
+
+   def circle_area
+      a * a * 3,14
+   end
+
+   def rectangle_area
+      a * a
+   end
+
+   def cal_area
+      case @name
+      when "circle"
+	circle_area
+      when "rectangle"
+	rectangle_area
+      else
+	"can not calculate the area"
+      end
+   end
+end
+
+
+# GOOD
+class Area
+   attr_accessor :a
+
+   def initialize
+       @a = a
+   end
+
+   def cal_area
+      raise "SYSTEM ERROR: method missing"
+   end
+end
+
+class Circle < Area
+   def cal_area
+     a * a * 3,14
+   end
+end
+
+class Rectangle < Area
+   def cal_area
+     a * a
+   end
+end
+
+# Alternative Classes with Different Interfaces
+# BAD
+
+class Person
+   def learn
+	# do_something
+   end
+
+   def go
+       # go with two legs
+   end
+end
+
+class Elephant
+   def eat
+	# eat plant
+   end
+
+   def run
+	# go with four legs
+   end
+end
+
+# GOOD
+class Animal
+    def move
+	raise "You need override this function"
+    end
+end
+
+class Person < Animal
+   def learn
+	# do_something
+   end
+
+   def move
+	# go with two legs
+   end
+end
+
+class Elephant < Animal
+   def eat
+	# eat plant
+   end
+
+   def move
+	# go with four legs
+   end
+end
+