Ruby: NoMethodError, but why? - ruby

Question

I was working on a simple Pi Generator while learning Ruby, but I kept getting NoMethodError on RubyMine 6.3.3, so I decided to make a new project and new class with as simple as possible, and I STILL get NoMethodError. Any reason?
class Methods
def hello (player)
print "Hello, " << player
end
hello ("Annie")
end
And the error I get is:
C:/Users/Annie the Eagle/Documents/Coding/Ruby/Learning Environment/methods.rb:5:in `<class:Methods>': undefined method `hello' for Methods:Class (NoMethodError)

Answer 1

You have defined an instance method and are trying to call it as a method of a class. Thus you need to make the method hello a class method, not an instance method of the class Methods.
class Methods
def self.hello(player)
print "Hello, " << player
end
hello("Annie")
end
Or, if you want to define it as instance method then call it as below :
class Methods
def hello(player)
print "Hello, " << player
end
end
Methods.new.hello("Annie")

Answer 2

You're trying to call an instance method as a class method.
Here's some code that illustrates the difference between the two in ruby:
class Person
# This is a class method - note it's prefixed by self
# (which in this context refers to the Person class)
def self.species
puts 'Human'
# Note: species is OK as a class method because it's the same
# for all instances of the person class - ie, 'Bob', 'Mary',
# 'Peggy-Sue', and whoever else, are ALL Human.
end
# The methods below aren't prefixed with self., and are
# therefore instance methods
# This is the construct, called automatically when
# a new object is created
def initialize(name)
# #name is an instance variable
#name = name
end
def say_hello
puts "Hello from #{#name}"
end
end
And now try it out, calling the methods...
# Call a class method...
# We're not referring to any one 'instance' of Person,
Person.species #=> 'Human'
# Create an instance
bob = Person.new('Bob')
# Call a method on the 'Bob' instance
bob.say_hello #=> 'Hello from Bob'
# Call a method on the Person class, going through the bob instance
bob.class.species #=> 'Human'
# Try to call the class method directly on the instance
bob.species #=> NoMethodError
# Try to call the instance method on the class
# (this is the error you are getting)
Person.say_hello #=> NoMethodError

Answer 3

You've created an instance method, but you're calling a class method. In order to call hello("Annie"), you have to make an instance of Methods. For instance:
class Methods
def self.hello(player)
print "Hello, " << player
end
end
my_method = Methods.new
my_method.hello("Annie")
This would output Hello, Annie

Answer 4

By defining a method with def method_name args you are defining a instance method that will be included in every object of that class, but not in the class itself.
On the other hand, by def self.method_name args you will get a class method that will be directly in the class, without the need of instanciate an object from it.
So If you have this:
Class Test
def self.bar
end
def foo
end
end
You can execute the instance method this way:
a = Test.new
a.foo
And as for the class one should be:
Test.foo