1. A method comprising: receiving a request to perform a live code update for an earlier iteration of an application that is currently running on an application computer, wherein the earlier iteration of the application includes a user class, the user class being a direct subclass of a system superclass in a class hierarchy of the application; compiling a subset of source code defining a subsequent iteration of the application to produce updated application bytecode; identifying a change, in the updated application bytecode, to the user class as defined by the subsequent iteration of the application; generating, in the updated application bytecode, an instance representation class that inherits from the system superclass; replacing, in the updated application bytecode, each instance of the user class with a respective instance of the generated instance representation class; generating, in the updated application bytecode, a method representation subclass having a representation method that is defined by a program method of the user class in the subsequent iteration of the application; replacing, in the representation method in the updated application bytecode, one or more original references to an instance of the user class with one or more corresponding references to respective instances of the generated instance representation class; adding, to the updated application bytecode, the method representation subclass; and providing the updated application bytecode to a live code update service configured to update the earlier iteration of the application to the subsequent iteration of the application using the updated application bytecode while the application is running on the application computer.