Classes and Instances

Classes and Instances

In this lesson — part of Objects and Classes — you'll learn classes and instances in Ruby and why it matters in real work.

Why it matters

Classes bundle data and behavior together — the core of object-oriented design.

Key ideas

• Classes and instances
• Fields and methods
• Constructors
• Encapsulation

In practice

Here's how it looks in idiomatic Ruby:

class Counter
  attr_reader :count          # generates a reader method
  def initialize(start = 0)
    @count = start            # @count is an instance variable
  end
  def increment
    @count += 1
  end
end
c = Counter.new
c.increment
puts c.count                  # => 1

Ruby note: Instance state lives in @-prefixed variables, initialize is the constructor invoked by .new, and attr_reader/_accessor generate getter/setter methods.

Try it yourself

Exercise: In Ruby, write a Bank Account class with deposit and withdraw methods.

Recap

You now understand classes and instances and can apply it in Ruby. Mark this lesson complete and continue to the next one.