Difference between Groovy def and Java Object?

I'm trying to figure out the difference between

Groovy:

def name = "stephanie"

Java:

Object name = "stephanie"

as both seem to act as objects in that to interact with them i have to cast them to their original intended type.

I was originally on a search for a java equivalent of C#'s dynamic class ( Java equivalent to C# dynamic class type? ) and it was suggested to look at Groovy's def

for example my impression of groovy's def is that I could do the following:

def DOB = new Date(1998,5,23);
int x = DOB.getYear();

however this wont build

thanks,steph

Solution edit: Turns out the mistake iw as making is I had a groovy class wtih public properties (in my example above DOB) defined with def but then was attemping to access them from a .java class(in my example above calling .getYear() on it). Its a rookie mistake but the problem is once the object leaves a Groovy file it is simply treated as a Object. Thanks for all your help!