One embodiment of the present invention provides a system that initializes system classes for a virtual machine during build time for the virtual machine, so that portions of the system classes can be stored in Read Only Memory (ROM). During virtual machine build time, the system loads system classes for the virtual machine. Next, the system identifies which of the system classes can be initialized at build time and then initializes the identified system classes. The system then stores portions of the system classes in a ROM image, so that the portions of the system classes can be accessed from the ROM image during subsequent run-time execution of the virtual machine. In this way, this embodiment of the present invention reduces the amount of time required to initialize system classes during run-time execution of the virtual machine.