According to the preferred embodiments, an apparatus and method is described for creating a real-time class package to class archive file mapping index that improves the performance of a class loader to load needed classes in an object oriented programming environment. In preferred embodiments, the class loader includes a mapping mechanism that creates and maintains a real-time class package to file archive mapping index. In preferred embodiments, the mapping mechanism optimizes access to the file archive mapping index. In a preferred embodiment, when the mapping mechanism finds a entry in the file archive mapping index for the package, but the class is not found, the class is searched in the class path beginning from the last file archive listed in the index to optimize the search. In other embodiments, the class loader includes a large package list that is used to further optimize access to the archive index.