JDK 11 is the latest release of the JDK (Java Development Kit). There are several changes since JDK 8 that will require projects to update their dependencies or build tools. Many open source projects have resolved these issues when adding support for JDK 9 and 10. For most projects that have been updating their dependencies regularly, the upgrade process to JDK 11 shouldn’t be too difficult. Last year I wrote a guide on upgrading Clojure projects to Java 9.