Consider the following code
class Square def initialize(side_length) @side_length = side_length end def area @side_length * @side_length end end
The area method is made available in all objects of class Square, so it's considered to be an object method.
Here's a simple demonstration of a class method:
class Square def self.test_method #class method puts "Hello from the Square class!" end # from w w w .j a va2 s .com def test_method #instance method puts "Hello from an instance of class Square!" end end Square.test_method Square.new.test_method
Here, Square class has two methods.
The first is a class method, and the second is an instance method.
They both have the same name of test_method.
The class method is denoted with self where self represents the current class.
def self.test_method defines the method as being specific to the class.
With no prefix, methods are automatically instance methods.
Alternatively, you could define the method like so:
class Square def Square.test_method puts "Hello from the Square class!" end end
The style ClassName.method_name versus self.method_name comes down to personal preference.