The methods you’ve been using so far have been instance methods. An instance method belongs to a specific instance of a class—in other words, to an individual object. It is also possible to write class methods. (Some other languages refer to this kind of method as a static method.) A class method belongs to the class itself. To define a class method, you must precede the method name with the class name and a full stop.

class_methods1.rb

class MyClass
   def MyClass.classMethod
      puts( "This is a class method" )
   end

   def instanceMethod
      puts( "This is an instance method" )
   en
end

You should use the class name when calling a class method:

MyClass.classMethod

A specific object cannot call a class method. Nor can a class call an instance method:

MyClass.instanceMethod        #=> Error! This is an 'undefined method'
ob.classMethod                #=> Error! This is an 'undefined method'