Computer Science Programming Basics in Ruby

10.4 Accessing the Superclass

In many cases, the overriding methods will have similar functionality to the methods they override. It is counterproductive to the concept of inheritance to just rewrite the same methods again with slightly altered code. Inheritance exists to make code reuse as easy as possible. As such, it provides a way to avoid rewriting the superclass method. Simply insert the word super with all the parameters that would be used to call the superclass method bearing the same name wherever you would like the superclass’s method, just like the initialize method. Applying this to our new SavingsAccount class, we get the code in Example 10-3.

Example 10-3. SavingsAccount version 3

     1 require_relative '../chapter_09/account_5.rb'
     2 
     3 class SavingsAccount < Account
     4 	def initialize(balance, name, phone_number, interest, minimum)
     5 		super(balance, name, phone_number)
     6 		@interest = interest
     7 		@minimum = minimum
     8 	end
     9 
    10 	def accumulate_interest
    11 		@balance += @balance * @interest
    12 	end
    13 
    14 	def withdraw(amount)
    15 		if (@balance - amount >= @minimum)
    16 			super(amount)
    17 		else
    18 			puts "Balance cannot drop below: " + @minimum.to_s
    19 		end
    20 	end
    21 end

In our example, obviously the benefits seem minimal. However, for complex programs, the advantages of using predefined classes are tremendous. Not only are we saving ourselves the time of rewriting the class, but we are also making code maintenance easier. If the withdraw method needs to be updated, we can update it in ...