Multi-release jar files without multiple sets of source code

Question

I want to create a multi-release JAR file for a library. I will build the MRJAR using maven - and initially it will contain Java 8 and Java 9 class files.

BUT - I do not want to maintain two separate sets of source code (eg in src/main/java-8 and src/main/java-9 ). Is it possible to have all of the Java-9 files in eg src/main/java and only the ones which differ in eg src/main/java-8 ?

Ideally, the full source code would then be organized as:

+ pom.xml
+ src
  + main
    + java
      <full java-9 source code>
    + java-8
      <overriding .java files which can only be compiled with java-8>

Answer 1

I do not want to maintain two separate sets of source code

You have to, so you can compile the Java 8 files separately from the Java 9 files.

Implied in the question (the way I read it), but not explicitly stated, is that you have two copies of the files that don't differ . You certainly don't need that.

Is it possible to have all of the Java-9 files in eg src/main/java and only the ones which differ in eg src/main/java-8?

That wouldn't make any sense, because all the files that don't differ must be Java 8 files, not Java 9 files.

Do the opposite.