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JEP 213 may affect source code that uses underscore ("_") as an identifier. Its use generated a warning as of Java SE 8, and has been turned into an error in JDK 9.

Modular Java Application Packaging

JEP 275 may affect code that uses the javapackager tool. The packager will only create applications that use the JDK 9 runtime.

Module System

JEP 261 may affect source code that is not compiled with the javac compiler using the -source, -target or -release options to select the use of legacy mode. 

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