05 ruby classes

RUBY CLASSES AND OBJECTS
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Ruby is a perfect Object Oriented Programming Language. The features of the object-oriented programming language
include:

Data Encapsulation:

Data Abstraction:

Polymorphism:

Inheritance:

These features have been discussed in Object Oriented Ruby.

An object-oriented program involves classes and objects. A class is the blueprint from which individual objects are
created. In object-oriented terms, we say that your bicycle is an instance of the class of objects known as bicycles.

Take the example of any vehicle. It comprises wheels, horsepower, and fuel or gas tank capacity. These characteristics
form the data members of the class Vehicle. You can differentiate one vehicle from the other with the help of these
characteristics.

A vehicle can also have certain functions, such as halting, driving, and speeding. Even these functions form the data
members of the class Vehicle. You can, therefore, define a class as a combination of characteristics and functions.

A class Vehicle can be defined as:

Class Vehicle
{
Number no_of_wheels
Number horsepower
Characters type_of_tank
Number Capacity
Function speeding
{
}
Function driving
{
}
Function halting
{
}
}

By assigning different values to these data members, you can form several instances of the class Vehicle. For example,
an airplane has three wheels, horsepower of 1,000, fuel as the type of tank, and a capacity of 100 liters. In the same
way, a car has four wheels, horsepower of 200, gas as the type of tank, and a capacity of 25 litres.

Defining a Class in Ruby:

To implement object-oriented programming by using Ruby, you need to first learn how to create objects and classes in
Ruby.

A class in Ruby always starts with the keyword class followed by the name of the class. The name should always be in
initial capitals. The class Customer can be displayed as:

class Customer

end

You terminate a class by using the keyword end. All the data members in the class are between the class definition and
the end keyword.

Variables in a Ruby Class:

Ruby provides four types of variables:

Local Variables: Local variables are the variables that are defined in a method. Local variables are not available
outside the method. You will see more detail about method in subsequent chapter. Local variables begin with a
lowercase letter or _.

Instance Variables: Instance variables are available across methods for any particular instance or object. That
means that instance variables change from object to object. Instance variables are preceded by the at sign (@)
followed by the variable name.

Class Variables: Class variables are available across different objects. A class variable belongs to the class and is
a characteristic of a class. They are preceded by the sign @@ and are followed by the variable name.

Global Variables: Class variables are not available across classes. If you want to have a single variable, which is
available across classes, you need to define a global variable. The global variables are always preceded by the
dollar sign ($).

Example:

Using the class variable @@no_of_customers, you can determine the number of objects that are being created. This
enables in deriving the number of customers.

class Customer
@@no_of_customers=0
end

Creating Objects in Ruby using new Method:

Objects are instances of the class. You will now learn how to create objects of a class in Ruby. You can create objects in
Ruby by using the method new of the class.

The method new is a unique type of method, which is predefined in the Ruby library. The new method belongs to the
class methods.

Here is the example to create two objects cust1 and cust2 of the class Customer:

cust1 = Customer. new
cust2 = Customer. new

Here, cust1 and cust2 are the names of two objects. You write the object name followed by the equal to sign (=) after
which the class name will follow. Then, the dot operator and the keyword new will follow.

Custom Method to create Ruby Objects :

You can pass parameters to method new and those parameters can be used to initialize class variables.

When you plan to declare the new method with parameters, you need to declare the method initialize at the time of the
class creation.

The initialize method is a special type of method, which will be executed when the new method of the class is called

with parameters.

Here is the example to create initialize method:

class Customer
@@no_of_customers=0
def initialize(id, name, addr)
@cust_id=id
@cust_name=name
@cust_addr=addr
end
end

In this example, you declare the initialize method with id, name, and addr as local variables. Here def and end are used
to define a Ruby method initialize. You will learn more about methods in subsequent chapters.

In the initialize method, you pass on the values of these local variables to the instance variables @cust_id, @cust_name,
and @cust_addr. Here local variables hold the values that are passed along with the new method.

Now you can create objects as follows:

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

Member Functions in Ruby Class:

In Ruby, functions are called methods. Each method in a class starts with the keyword def followed by the method
name.

The method name always preferred in lowercase letters. You end a method in Ruby by using the keyword end.

Here is the example to define a Ruby method:

class Sample
def function
statement 1
statement 2
end
end

Here statement 1 and statement 2 are part of the body of the method function inside the class Sample. These statments
could be any valid Ruby statement. For example we can put a method puts to print Hello Ruby as follows:

class Sample
def hello
puts "Hello Ruby!"
end
end

Now in the following example create one object of Sample class and call hello method and see the result:

#!/usr/bin/ruby

class Sample
def hello
puts "Hello Ruby!"
end
end

# Now using above class to create objects
object = Sample. new
object.hello

This will produce following result:

Hello Ruby!

Simple Case Study:

Here is a case study if you want to do more practice with class and objects:

Ruby Class Case Study

05 ruby classes

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