You probably have some Java 8 (or earlier) code on your hands. And you are probably wondering what you'll need to do to get this to work with Java 9. When the Java 9 specification was going through the Java Community Process (JCP), there was some concerns in the developer community about just this. Will the legacy Java code work as-is in Java 9? If there are changes to be made, how much time and effort would they consume? Fortunately, Java has a great track record of maintaining backward compatibility, and that continues even with such major changes that have been brought into the language with the new modularity features. However, since Java 9 is one of the biggest overhauls to the Java internals, there might be some work that needs to be done. The amount of work depends primarily on two factors--the nature of migration you are trying to perform...
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