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Chapter 1. Migration to Red Hat build of OpenJDK 21

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The Migrating to Red Hat build of OpenJDK 21 from earlier versions guide provides information on how to upgrade your Java applications in Red Hat build of OpenJDK version 8, 11, or 17 to Red Hat build of OpenJDK 21.

This guide describes changes in the Red Hat build of OpenJDK 21 release, including new features and deprecated or removed APIs, that might impact your migration from an earlier version of Red Hat build of OpenJDK.

If you are migrating from Red Hat build of OpenJDK 11 or earlier, this guide also describes the changes that were introduced in Red Hat build of OpenJDK 17. If you want to migrate from Red Hat build of OpenJDK 11 or earlier, ensure that you also familiarize yourself with the major differences between versions 11 and 17.

If you are migrating from Red Hat build of OpenJDK 8, this guide also describes the changes that were introduced in Red Hat build of OpenJDK 11. If you want to migrate from Red Hat build of OpenJDK 8, ensure that you also familiarize yourself with the major differences between versions 8 and 11.

The OpenJDK project is known for its conservative approach to providing updates and for providing backward compatibility. However, to guarantee the evolution, security and stability of the project, the Red Hat build of OpenJDK project might sometimes introduce a few incompatibilities across major releases of Red Hat build of OpenJDK. These incompatibilities are relevant for the following scenarios:

  • When you use APIs that are considered obsolete or unsecure
  • When you access internals of the project that are considered implementation details and not public or supported API details
Note

Red Hat recommends that you migrate to the latest supported Red Hat build of OpenJDK distribution.

1.1. About Red Hat build of OpenJDK distributions

OpenJDK is the free and open source reference implementation of the Java Platform, Standard Edition (Java SE). Red Hat build of OpenJDK distributions are based on the upstream OpenJDK 8u, OpenJDK 11u, OpenJDK 17u, and OpenJDK 21u projects. The Shenandoah Garbage Collector is included in all supported versions of Red Hat build of OpenJDK.

All versions of Red Hat build of OpenJDK provide the following benefits:

Multi-platform
Red Hat build of OpenJDK is supported on RHEL and Microsoft Windows, so you can standardize applications on a single Java platform across desktop, data center, and hybrid cloud environments.
Frequent releases
Red Hat delivers quarterly updates of JRE and JDK for Red Hat build of OpenJDK 8, Red Hat build of OpenJDK 11, Red Hat build of OpenJDK 17, and Red Hat build of OpenJDK 21 distributions. These updates are available as archive, RPM, and Windows MSI-based installer files and container images.
Long-term support
Red Hat supports the recently released Red Hat build of OpenJDK 8, Red Hat build of OpenJDK 11, Red Hat build of OpenJDK 17, and Red Hat build of OpenJDK 21 distributions.

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