No exhaustive coding guidelines have been published for the OpenJDK project. Sub-components in the OpenJDK come from a variety of sources with their own diverse set of guidelines.
An incomplete development guide can be found here:
Some organizational guides and style guides can be found here:
Code Reviews and Code Quality
Quality of code contributions is controlled by Reviewers in charge of the code repository of a given OpenJDK subproject. Up-streamed changes from contributors must pass through those gatekeepers who apply the processes defined by the JCP (Java Community Process, https://jcp.org/) for approving changes and new features.
Overall quality and compatibility are assured through the TCK suite. All new features, compatibility breaking changes and reproduceable bugs must be submitted with TCK tests cases.