Given a class, see if instance has method (Ruby)

I don't know why everyone is suggesting you should be using instance_methods and include? when method_defined? does the job.

class Test
  def hello; end
end

Test.method_defined? :hello #=> true

NOTE

In case you are coming to Ruby from another OO language OR you think that method_defined means ONLY methods that you defined explicitly with:

def my_method
end

then read this:

In Ruby, a property (attribute) on your model is basically a method also. So method_defined? will also return true for properties, not just methods.

For example:

Given an instance of a class that has a String attribute first_name:

<instance>.first_name.class #=> String

<instance>.class.method_defined?(:first_name) #=> true

since first_name is both an attribute and a method (and a string of type String).

You can use method_defined? as follows:

String.method_defined? :upcase # => true

Much easier, portable and efficient than the instance_methods.include? everyone else seems to be suggesting.

Keep in mind that you won't know if a class responds dynamically to some calls with method_missing, for example by redefining respond_to?, or since Ruby 1.9.2 by defining respond_to_missing?.