Java major version to install, for example 21 or 25. 21 or newer is recommended; older versions are allowed but flagged with a warning. The field is editable: the dropdown lists common versions, but you can type any version your agent image's apt repositories provide, so new releases work without a plugin update. The package installed is openjdk-<version>-jre-headless (OpenJDK) or java-<version>-amazon-corretto-jdk (Corretto). A version that is not available in those repositories fails the install with an apt error in the agent launch log. Ignored when Java Distribution is None.