Computer Science Programming Basics in Ruby

9.3 Data and Methods

Objects are made up of two important concepts: the data the object holds (the instance variables) and the actions the object can perform (the methods).

9.3.1 Grouping Data and Methods

The previous section detailed how to create and instantiate an object of an Account class, and while reading it you might have been thinking to yourself, “How was I supposed to know that an Account class needs a balance variable?” The answer is that no class requires any particular piece of data, but classes are used to group related pieces of data together, and it only makes sense that an account has a balance. Likewise, there are other things that would come as a part of a bank account. Depending on the nature of the bank account, the type of data included would change. For example, a savings account wouldn’t necessarily include the same data as a checking account. Regardless, we are talking about a generic bank account, and additional data possibly included are name, phone number, Social Security number, minimum balance, and maximum balance. We now introduce two additional instance variables to our Account class, as shown in Example 9-3.

Example 9-3. Account version 2

    1 class Account
    2 	def initialize(balance, name, phone_number)
    3 		@balance = balance
    4 		@name = name
    5 		@phone_number = phone_number
    6 	end
    7 end

Gem of Wisdom

Note that the instance variables balance, name, and phone_number are assigned in the order the parameters were passed to the initialize method; however, ...