You Must Avoid Final Field Mutation

JDK 26 / JEP 500 is restricting final field mutation via reflection, and Java projects need to migrate away from this practice. The post covers alternatives for each common use case: platform serialization (use records, readResolve, or serialization proxy pattern), custom serialization frameworks (limit to records or use record proxies), dependency injection (switch to constructor injection), and cloning (use copy constructors or static factory methods instead). The core advice is to embrace constructors as the single point of instance creation, since they properly enforce invariants and work naturally with final fields. The --enable-final-field-mutation flag exists as a last resort for cases with no other solution.