Abstract: In dynamically upgrading an original concentrated executable computer software code with an upgrade bytecode, list processing and indexing is used to create indexes of various code structures within the upgrade bytecode. Preferably, index listings for each of the code structures are created. The index listings contain listings of identifiers corresponding to the particular instances of the respective code structures in the upgrade bytecode and index references corresponding to each of the identifiers included in the listing. The upgrade bytecode is reduced in size by replacing identifiers representing code structures in the upgrade bytecode with the corresponding index references. The concentrated upgrade bytecode is then integrated with the original concentrated bytecode, and the index listings formed during concentration of the upgrade bytecode are added to the virtual table as a record.