I'm migrating multiple projects from Java 8 to Java 11 and I was wondering if Java 8 is forward compatible with Java 11. In other words, is it possible to use artifacts compiled against Java 11 in Java 8 projects?

CodePudding user response：

You can run projects that were compiled for Java 8 in Java 11 runtime.

You can run projects that were compiled for Java 11 in Java 8 runtime if you properly set the --target during compilation to target JDK 8 or less. This will of course also limit the set of features supported in the source code.

Generally, earlier versions of JDK are supported on later runtimes (i.e. Java 11 should run on Java 17), but there are some caveats because some of the features might get deprecated or changed. Always read the release notes and test before you do that.

CodePudding user response：

No, you cannot execute Java 11 bytecode on an older (any older) JVM. This has always been the case. Each new major compiler release has a new bytecode format that won't execute on older runtimes.

You CAN however execute bytecode from an older version on a newer JVM, so executing Java 8 bytecode on a Java 11 runtime is quite possible and you can thus use Java 8 (or older) compiled libraries in Java 11 projects, if the dependency requirements are met.

Do however keep in mind that Java 9 removed a number of packages from the core libraries that were in there with Java 8, so you may need to supply new dependencies from third parties to replace those. Most notable of those (but certainly not the only ones) are XML parsers.