Changing the behaviour of a Java app dynamically using Groovy

I am investigating methods of dynamically modifying the behaviour of a Java application (specifically, I'm trying to make a Minecraft mod that allows users to modify the behaviour of the objects they find by writing code without the need to restart the game) and I stumbled upon Groovy. My question is: is it possible to integrate Java and Groovy in such way they "share" objects? (I'm thinking about having a specific set of classes that are actually Groovy code so you can change the code during runtime, similarly to what you can do in any Smalltalk implementation)