array_enum.rb

require 'java'
puts "Starting array_enum"
class ArrayEnumeration
  include java.util.Enumeration
  def initialize(arr)
    @arr = arr
    @pos = 0
  end
  def hasMoreElements
    @pos < @arr.length
  end
  def nextElement
    raise java.util.NoSuchElementException.new("no more elements") unless hasMoreElements
    pos = @pos
    @pos += 1
    @arr[pos]
  end
end

class ProducesEnumeration
  def makeEnum
    ArrayEnumeration.new([])
  end
end

java_src = <<SRC
import java.util.Enumeration;
public class UsesEnumeration {
  public static interface ProducesEnumeration {
    Enumeration makeEnum();
  }
  public static Enumeration makeEnum(ProducesEnumeration pe) {
    return pe.makeEnum();
  }
}
SRC
File.open("UsesEnumeration.java", "wb") {|f| f << java_src}
system("javac -d . UsesEnumeration.java")
import "UsesEnumeration"

require 'test/unit'

class ArrayEnumerationTest < Test::Unit::TestCase
  def test_has_underscored_methods
    array_enum = UsesEnumeration.makeEnum(ProducesEnumeration.new)
    p array_enum
    p array_enum.methods.grep(/has|next/)
    assert_nothing_raised {
      assert !array_enum.has_more_elements
    }
  end
end