Java Compiler Superpowers: Annotation Processors, Error Prone, and Coding Agents

Why we picked it

Java has compiler superpowers that most developers never use directly. **Did you know you can write code that runs inside** ***javac***? That you can inspect classes, methods, types, annotations, and syntax trees while the compiler is working? That you can generate source code, report custom compiler errors, or write checks that understand what code means rather than just what text it contains? Most Java developers have already used these capabilities indirectly. Frameworks like MapStruct and Spring Boot extend the compiler to generate code and metadata during compilation, making them feel like ordinary framework features when they’re actually compiler extensions. In this talk we’ll explore another powerful compiler extension: **Error Prone**, Google’s open-source static analysis framework for Java. Error Prone runs inside javac, understands the structure of your code, catches bug patterns at compile time, and can be extended with custom rules that report diagnostics, suggest fixes,