Here's a script from the Groovy book that explains expandos and makes some sense of why you might want to mess with spinning up methods at runtime. - http://groovy.codehaus.org/ExpandoMetaClass+-+Dynamic+Method+Names The first example might help you pull off some interactive UI. The second lends to a more fluid api. Run that in your console and smoke it. import org.springframework.web.util.HtmlUtils class HTMLCodec { static encode = { theTarget -> HtmlUtils.htmlEscape(theTarget.toString()) } static decode = { theTarget -> HtmlUtils.htmlUnescape(theTarget.toString()) } } //So what we do with these classes is to evaluate the convention and add //"encodeAsXXX" methods to every object based on the first part of the //name of the codec class such as "encodeAsHTML". The pseudo code to achieve this is below: def classes = [HTMLCodec] def codecs = classes.findAll { it.name.endsWith('Codec&