[groovy-user] modifying java class

Hi,
I have a groovy class as follows:
class GroovyInterceptor  {
	def run_it() {
		def b = [ doCallService: { "no service!!!" } ] as PlainOldJavaObject
		println b.myMethod("arg")
	}		
}

where PlainOldJavaObject is a java class:
public class PlainOldJavaObject  {
    public String myMethod(String x) {
        System.out.println("myMethod: args: " + x);
    	return doCallService(x);
    }

    public/protected/private String doCallService(String x) {
    	System.out.println("doCallService: args: " + x);
    	return "Hello from doCallService";
    }
}

The object in "b" is of class PlainOldJavaObject1_groovyProxy (result of
b.getClass.getName()) and b.myMethod("arg") calls the overridden
doCallService - but only when it is public or protected, not when defined as
private.
So how is this class PlainOldJavaObject1_groovyProxy generated? And what
happens when doCallService is private?

Thanks a lot for help