OpenJDK

OpenJDK is the open-source implementation of the Java Platform, Standard Edition (Java SE) and serves as the official reference implementation for Java SE specifications. It includes the Java Development Kit and the Java Runtime Environment, and is developed as a community project under the GNU General Public License version 2 with the Classpath Exception, which allows linking with non-GPL code.

OpenJDK originated in 2006 as a collaboration initiated by Sun Microsystems to create an open-source Java platform. After Oracle acquired Sun, development continued under the OpenJDK project with governance by a Governing Board that includes Oracle and community members. The project emphasizes compatibility with Java SE through the Java SE Technology Compatibility Kit (TCK).

The OpenJDK distribution includes the HotSpot JVM, the Java class libraries, and development tools such as javac, javadoc, and jdb. It follows a six-month feature release cadence, with Long-Term Support (LTS) releases occurring at intervals (notably Java 8, 11, 17, and 21). Since Java 9, the platform has included modularization (the JPMS), reorganizing the JDK into modules. OpenJDK builds are available for Windows, macOS, and Linux across multiple architectures.

OpenJDK serves as the upstream source for many commercial and community distributions. Oracle JDK is a commercial distribution derived from OpenJDK, while other vendors provide binary builds from the same codebase, such as Adoptium Temurin, Amazon Corretto, Azul Zulu, SAP SapMachine, and others. While features and support may vary by distribution, all OpenJDK-based products aim for Java SE compatibility and broad platform support.