Comprehensive Guide to Upgrading from JDK 8 to JDK 11: Benefits, New Features, GC Performance, and Migration Steps

Since the release of Java 11 in September 2018, it has become the first LTS version after Java 8, prompting many teams to consider upgrading. The article begins by answering why to upgrade, emphasizing better garbage‑collection mechanisms, faster class loading, and long‑term support.

Performance improvements are highlighted with benchmark data showing G1GC speed up by 16.1% and ParallelGC by 4.5% compared to Java 8, based on OptaPlanner tests. The author also cites New Relic statistics that more than 56% of applications already run on JDK 11.

New language and API features introduced in Java 11 include local‑variable type inference (var), enhanced lambda expressions, HTTP/2 client, additional String methods (isBlank, lines, strip, repeat, etc.), Files API extensions, InputStream.transferTo, and collection factory methods such as List.of and Map.of.

Modularization (JPMS) is discussed as a way to encapsulate code, improve maintainability, and reduce runtime errors, though the article advises caution because the ecosystem around modules is still immature and many middle‑wares are built for JDK 8.

Garbage‑collector changes are covered: Java 11 switches the default GC to G1 (with the option to use ParallelGC), deprecates CMS, and introduces ZGC (still experimental). Recommendations are given based on machine memory size (ParallelGC for < 8 GB, G1 for larger machines).

Migration steps are organized into four sub‑sections: evaluating new applications first, choosing OpenJDK 11 (free for commercial use), configuring the appropriate GC flags (e.g., -XX:+UseG1GC or -XX:+UseParallelGC ), and validating the upgrade with unit tests, regression tests, and optional load testing.

The article also provides a practical module‑system example, showing directory structures and module-info.java files for two modules (module‑a and module‑b), and explains common pitfalls such as missing SPI dependencies, split‑package conflicts, and how to resolve them.

In the conclusion, the author recommends upgrading to JDK 11 for its performance and feature benefits while advising against using modularization in production until the ecosystem matures, and hints at future exploration of JDK 17’s ZGC.