jruby-9.1.2.0 :001 > [1, 2, 3].to_java.is_a? ArrayJavaProxy
 => true 
jruby-9.1.2.0 :002 > [1, 2, 3].to_java.is_a? Enumerable
 => true 
jruby-9.1.2.0 :003 > [1, 2, 3].to_java.last
NoMethodError: undefined method `last' for java.lang.Object[1, 2, 3]@1139b2f3:#<Class:0x7a69b07>
    from (irb):3:in `<eval>'
    from org/jruby/RubyKernel.java:983:in `eval'
    from org/jruby/RubyKernel.java:1290:in `loop'
    from org/jruby/RubyKernel.java:1103:in `catch'
    from org/jruby/RubyKernel.java:1103:in `catch'
    from /opt/local/rvm/rubies/jruby-9.1.2.0/bin/irb:13:in `<top>'
jruby-9.1.2.0 :004 > [1, 2, 3].to_java.count
 => 3 
jruby-9.1.2.0 :005 > [1, 2, 3].to_java.count { |e| e>=2  }
 => 2