Jikes Bytecode Toolkit is a 100% Java class library that enables Java programs to create, read, and write binary Java class files and to query and update a single, high-level representation of the collection of them, including relationships among them. These features allow the development of tools that report on what APIs the classes use, reorder and change instructions, merge or extend classes, add customized instrumentation (similar to profilers), analyze control and data flow, etc.