Java 26 will issue run-time warnings when a final field is mutated through reflection. This prepares for a future change that will make such final field mutations illegal by default to improve Java’s integrity, specifically the keyword final. This will have beneficial effects on maintainability, security, and performance. While the recommendation is to move away from final field mutation, the new permanent command-line option --enable-final-field-mutation allows it for selected modules. To ease migration, the more general but temporary option --illegal-final-field-mutation was also introduced.

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