A method and system that reduces the space allocated for internal data structures by a runtime engine. The internal data structures store member information for preloaded classes used by applications executed by the runtime engine. The system determines the different types of internal data structures represented in the classes and identifies thee possible values of each type's members. The system next determines the amount of space required to store the values for each type in a respective value table and the number of bits needed to index each entry of that table. The system determines based on the stored information whether occurrences of a member are optimally represented as a set of value table indices and a value table or, in the conventional manner, as a general variable that stores the member's value for each occurrence. The system then emits appropriate information for the member and its parent data structure.