Illustrates problem instantiating Ruby subclass of Java class w/different constructor arities.

jruby-2457.rb

require 'java'

java_import 'java.lang.Runnable'

class SampleRunnable
  
  include Runnable

  def initialize(greeting)
    @greeting = greeting
  end
  
  def run
    puts @greeting
  end
  
end

# new_thread = java.lang.Thread.new(SampleRunnable.new)
# new_thread.start
# new_thread.join

# Yields:
# >ruby jruby-2457.rb 
# ArgumentError: wrong number of arguments (0 for 1)
#   (root) at jruby-2457.rb:19


# Workaround:

class WorkaroundRunnable
  
  attr_accessor :greeting
  
  include Runnable

  def self.create_instance(greeting)
    instance = WorkaroundRunnable.new
    instance.greeting = greeting
    instance
  end
  
  def run
    puts @greeting
  end
  
end

new_thread = java.lang.Thread.new(WorkaroundRunnable.create_instance("I'm a workaround."))
new_thread.start
new_thread.join

# Yields:

# >ruby jruby-2457.rb
# I'm a workaround.

# The workaround is usually fine.  However, there may be cases where Ruby code is
# instantiating different classes, and assuming that it can call new with the
# parameter (in this case, the greeting param).