The following will create a Ruby class named Customer and declare two methods:

• display_details : This method is used to display customer details.
• total_no_of_customers : This method is used to display the total number of customers created in the system.

#!/usr/bin/ruby

class Customer
   @@no_of_customers = 0
   def initialize(id, name, addr)
      @cust_id = id
      @cust_name = name
      @cust_addr = addr
   end
   def display_details()
      puts "Customer id #@cust_id"
      puts "Customer name #@cust_name"
      puts "Customer address #@cust_addr"
   end
   def total_no_of_customers()
      @@no_of_customers += 1
      puts "Total number of customers: #@@no_of_customers"
   end
end

The display_details method contains three puts statements that display the customer ID, customer name and customer address. Among them, the puts statement:

puts "Customer id #@cust_id"

The text Customer id and the value of the variable @cust_id will be displayed on a single line.

When you want to display the text and value of an instance variable on a single line, you need to put a symbol (#) in front of the variable name of the puts statement. Text and instance variables with symbols (#) should be marked with double quotes.

The second method, total_no_of_customers, contains the class variable @@ no_of_customers. The expression @@ no_of_ customers + = 1 increases the variable no_of_customers by 1 each time the method total_no_of_customers is called. In this way, you will get the total number of customers in the class variable.

Now create two customers as follows:

cust1 = Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2 = Customer.new("2", "Poul", "New Empire road, Khandala")

Here, we create two objects of the Customer class, cust1 and cust2, and pass the necessary parameters to the new method. When the initialize method is called, the necessary properties of the object are initialized.

Once the object is created, you need to use two objects to call the methods of the class. If you want to call a method or any data member, you can write code as follows:

cust1.display_details()
cust1.total_no_of_customers()

The object name is always followed by a period, followed by the method name or data member. We have seen how to call two methods using the cust1 object. Using the cust2 object, you can also call two methods as follows:

cust2.display_details()
cust2.total_no_of_customers()

Save and execute the code

Now, put all the source code in the main.rb file as follows:

#!/usr/bin/ruby

class Customer
   @@no_of_customers = 0
   def initialize(id, name, addr)
      @@no_of_customers += 1
      @cust_id = id
      @cust_name = name
      @cust_addr = addr
   end
   def display_details()
      puts "Customer id #@cust_id"
      puts "Customer name #@cust_name"
      puts "Customer address #@cust_addr"
   end
   def total_no_of_customers()
      puts "Total number of customers: #@@no_of_customers"
   end
end

# Create Objects
cust1 = Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2 = Customer.new("2", "Poul", "New Empire road, Khandala")

# Call Methods
cust1.display_details()
cust1.total_no_of_customers()
cust2.display_details()
cust2.total_no_of_customers()

cust3 = Customer.new("3", "Raghu", "Madapur, Hyderabad")
cust4 = Customer.new("4", "Rahman", "Akkayya palem, Vishakhapatnam")
cust4.total_no_of_customers()

Next, run the program as follows:

$ ruby main.rb

This will produce the following result: