Migration Overview Migrating from Java 8 to Java 11 is the most common Java upgrade scenario. The migration has two distinct phases: Make it compile and run — fix incompatibilities introduced by Java 9–11 Modernise the code — adopt var, List.of(), String.isBlank(), and other new APIs Phase 1 is mandatory and blocks the upgrade. Phase 2 is optional and can happen incrementally. This guide focuses entirely on Phase 1. The 10-Step Migration Checklist [ ] 1.