gistfile1.txt

# Inheritance Weirdness:  I can get a couple of different errors, but no correct behavior out of the following code:

#!/usr/bin/env jruby -d

require 'java'
require '/Users/bradheintz/project/hadoop/current/lib/commons-logging-1.0.4.jar'
require '/Users/bradheintz/project/hadoop/current/lib/log4j-1.2.15.jar'
require '/Users/bradheintz/project/hadoop/current/hadoop-0.18.1-core.jar'

class MyMapper < org.apache.hadoop.mapred.MapReduceBase
  include org.apache.hadoop.mapred.Mapper
end

conf = org.apache.hadoop.mapred.JobConf.new


# The error I get depends on which of the following lines I end with.  I need to call conf.setMapperClass(), which is defined thus:
# public void setMapperClass(Class<? extends Mapper> theClass)

# If I do this:
conf.setMapperClass(MyMapper)

# I get this error:
# org/apache/hadoop/conf/Configuration.java:697:in `setClass': java.lang.RuntimeException: class org.apache.hadoop.mapred.MapReduceBase not org.apache.hadoop.mapred.Mapper (NativeException)
#         from org/apache/hadoop/mapred/JobConf.java:708:in `setMapperClass'
#         from sun/reflect/NativeMethodAccessorImpl.java:-2:in `invoke0'
#         from sun/reflect/NativeMethodAccessorImpl.java:39:in `invoke'
#         from sun/reflect/DelegatingMethodAccessorImpl.java:25:in `invoke'
#         from java/lang/reflect/Method.java:585:in `invoke'
#         from org/jruby/javasupport/JavaMethod.java:298:in `invokeWithExceptionHandling'
#         from org/jruby/javasupport/JavaMethod.java:259:in `invoke'
#         from org/jruby/java/invokers/InstanceMethodInvoker.java:44:in `call'
#         from org/jruby/runtime/callsite/CachingCallSite.java:280:in `cacheAndCall'
#         from org/jruby/runtime/callsite/CachingCallSite.java:116:in `call'
#         ...more stack elided...

# ...which looks like the inherited class is obscuring the interface.


# If I do this (which is closer to the actual Java call I'd use):
conf.setMapperClass(MyMapper.class)

# I get this error;
./implement.rb:18: for method setMapperClass expected [java.lang.Class]; got: [org.jruby.RubyClass]; error: argument type mismatch (TypeError)


# Fair enough, it wants a Java class.  But when I use this:
conf.setMapperClass(MyMapper.java_class)

# ...I get the same Java stack trace as above.