ruby class inheriting from a java class

j.rb

require 'java'
require 'jruby/core_ext'

# brew install hadoop
HADOOP_ROOT = "/usr/local/Cellar/hadoop/0.21.0/libexec/"
Dir.glob( File.join( HADOOP_ROOT, "**/*.jar" ) ).each do |jar|
  require jar
end

# http://hadoop.apache.org/mapreduce/docs/r0.21.0/api/org/apache/hadoop/mapreduce/Mapper.html
# org.apache.hadoop.mapreduce Class Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
Mapper = org.apache.hadoop.mapreduce.Mapper

class TestA < Mapper
end

puts "Ruby TestA class : #{TestA.name}"

puts "Test A Ancestors: #{TestA.ancestors.join(", ")}"

java_class = TestA.become_java!

if java_class.nil? then
  puts "become_java! returned nil"
  puts "TestA name = #{TestA.name}"
else
  puts java_class.interfaces.each { |i| puts i }
end

__END__
% ruby ./j.rb
Ruby TestA class : TestA
Test A Ancestors: TestA, Java::OrgApacheHadoopMapreduce::Mapper, Java::JavaLang::Object, ConcreteJavaProxy, JavaProxy, JavaProxyMethods, Object, Kernel
become_java! returned nil
TestA name = TestA