JOPA: Java compiler in C++, Jikes modernized to Java 6 with Claude (github.com)

A new fork modernizes Jikes — the classic C++ Java compiler — to support Java 5 and Java 6 language features, a project reportedly completed with heavy assistance from Anthropic’s Claude. The update adds generics (type-erasure semantics), enhanced for-loops, varargs, enums (with synthetic values()/valueOf()), autoboxing/unboxing, static imports, annotations, and emits classfile version 50.0 (Java 6) bytecode. It also preserves enhanced debug info (parameter names and locals via -g). The source builds with CMake (3.20+) and a C++17 compiler; optional iconv/ICU support is available, and the repo includes Nix/direnv helpers and several CMake toggles for debugging, floating-point emulation, encoding, and JVM-test toggles. For the AI/ML community this is notable for two reasons: first, it resurrects a lightweight, fast, C++-based Java toolchain useful for bootstrapping, compiler research, program-synthesis evaluation, and reproducible bytecode generation outside the JVM ecosystem. Second, it’s a concrete example of using a large language model to modernize nontrivial legacy systems—highlighting LLMs’ potential in code migration, refactoring, and maintaining complex C++ codebases. The fork keeps Jikes’s historical strengths (simplicity, speed, pedagogical value) while making it relevant for experiments that require Java 5/6 semantics or compact, analyzable compiler infrastructure.