jruby環境でgem install ruby-debug-baseとすると下記のようなエラーが出てくると思います。
Building native extensions. This could take a while... WARNING: JRuby does not support native extensions or the `mkmf' library. Check wiki.jruby.org for alternatives. extconf.rb:16: undefined method `create_makefile' for main:Object (NoMethodError) ERROR: Error installing ruby-debug-base: ERROR: Failed to build gem native extension. "C:/Program Files/NetBeans 6.8/ruby2/jruby-1.4.0/bin/jruby.exe" extconf.rb Gem files will remain installed in C:/Program Files/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/linecache-0.43 for inspection. Results logged to C:/Program Files/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/linecache-0.43/ext/gem_make.out
メッセージの通りJRubyは、NativeExtension をサポートしていないようです。
JRuby
Automatic instalation for JRuby is not supported yet. You need to install two gems to get it working following steps below:
1. Manually download the ruby-debug-base-0.10.3.1-java.gem from debug-commons to a local directory.
2. Install the Gem into your JRuby Gem repository:jruby -S gem install -l ruby-debug-base-0.10.3.1-java.gem
3. Now install ruby-debug-ide with:
jruby -S gem install --ignore-dependencies -v 0.4.6 ruby-debug-ide
See Troubleshooting section if you encounter problems.
モジュールを直接ダウンロードしてからインストールしたら良いみたい。