Avoiding Final Field Mutation

JDK 26 introduces warnings for reflective mutation of final fields via JEP 500, moving toward making final fields truly immutable. The post covers common scenarios where final fields are mutated through reflection — including platform serialization, custom serialization, dependency injection, and cloning — and provides concrete alternatives for each. Key recommendations include embracing constructor injection, using records as data carriers, adopting the serialization proxy pattern, and using copy constructors instead of Cloneable. New command-line flags `--enable-final-field-mutation` and `--illegal-final-field-mutation` are introduced for managing legacy code during the transition.