面试题与答案

1. Ruby on Rails is an open source full-stack web application framework written in the Ruby Programming Language. Rails is capable of gathering information using pages and applications from the web server and can interact with a database and can retrieve information from the database.

• This is a simple question based on complex concept. Here’s your chance to show off your theoretical knowledge and demonstrate that you can have an in depth conversation on class hierarchies, inheritance, methods, encapsulation, polymorphism, and more.

• Explaining this could take an hour or a few minutes – there’s no single correct answer here, save from being able to demonstrate your familiarity with OOP concepts.

• Class variables are created with the prefix ‘@@’ and are shared by all objects in a class.

• Instance variables are created with the prefix ‘@’ and belong to a single object within a class.

Class variables are created using the @@ prefix to denote the variable as class level. 

It works just like any other variable, however in the case of inheritance it works more like a static variable that is accessed across all variable instances.

Another example can be found here:

class DemoClass 
 @@my_var = nil
  def initialize
    @@my_var = "hello world"
  end
  def my_var
    puts @@my_var
  end
end
class Demo2Class < DemoClass
  def initialize
    @@my_var = "goodbye world"
  end
end
demo1 = DemoClass.new
demo1.my_var
demo2 = Demo2Class.new
demo2.my_var
demo1.my_var
The output would be as shown below:
hello world
goodbye world
goodbye world

Instance variables are defined using single @ symbol.

@foo = "Hello"

Within a class they can be declared as below:

class Animal
 attr_accessor :name, :age
end

Next you can query an object instance to find which instance variables it has.

anim = Animal.new
anim.instance_variables 
=> [ ]
anim.name="John"
anim.age = 3
 => [:@age, :@name] 

In the above case we did not put the @ symbol before the instance variables but it is implied. 

The ‘&&’ and ‘and’ are both logical and statements. They ‘&&’ operator has higher precedence though. Here’s an example of illustrate this in more detail:

foo = 3
bar = nil
a = foo and bar
# => nil
a
# => 3
a = foo && bar
# => nil
a
# => nil

Create a new file as shown below under: config/initializers/my_constants.rb

COLORS = ['white', 'red', 'green']

By default all methods are public, except the initialize(constructor) method.

You can make methods private using this declaration within your class:

class MyClass
    def method_public_here
    end
    PRIVATE# all methods that follow will be made private: not accessible for outside objects
    def method_private_here
    end
  end

The MVC framework is an age-old architecture pattern that works very well for most applications. Rails has adopted the MVC pattern in its inherent design.

Stated Simply:

a) Model — is where the data is — the database

b) Controller — is where the logic is for the application

c) View — is where the data is used to display to the user