Another almost-original sin that Java is working on fixing is the non-finality of the keyword `final`: In a future release, reflective mutation of final fields will fail unless explicitly allowed with the command-line option `--enable-final-field-mutation`. Now, in JDK 26, it's still possible but you'll get a warning. That behavior can be managed with the temporary option `--illegal-final-field-mutation`:

* `allow` lets you mutate final fields
* so does `warn`, which is the default on 26, but you'll get one warning per mutating module
* `debug` is like `warn` but for every mutation and with more details
* and finally, `deny` simulates the future where such mutation leads to an exception

JEP 500: https://openjdk.org/jeps/500
JDK 26: JDK 26: http://jdk.java.net/26

Come to *JavaOne 2026* in Redwood City (California, USA), March 17th-19th, and *get 100$ off* with code *J12026YTS* : https://www.oracle.com/javaone/

Java (Official Oracle)

Java is incrementally restricting reflective mutation of final fields. In JDK 26, such mutations still work but trigger a warning by default. The behavior is controlled via the temporary flag `--illegal-final-field-mutation` with four modes: `allow`, `warn` (default), `debug`, and `deny`. A future release will make mutation fail outright unless explicitly permitted via `--enable-final-field-mutation`. This change is tracked under JEP 500.

Reflective Final Field Mutation in #Java 26 #IJN #Coding