Major differences of OpenJDK 11 and OpenJDK 8

Solution Verified - Updated

Environment

  • OpenJDK 8
  • OpenJDK 11

Issue

  • What are the differences between OpenJDK 8 and OpenJDK 11?
  • Was there anything added or removed in JDK 11?

Resolution

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Major differences:

  • Log system: In OpenJDK 11, a.k.a Java 11, the log system was unified. See JDK 11 Logging mechanism with -Xlog Option

  • lib/ext and JRE directory: In OpenJDK 11, this directory was removed now with the existence of jlink support and the use of -classpath flag is necessary to add custom modules to the runtime. The solution How to create a Custom JRE using jlink explains the complete procedure to use jlink.

  • Several modules were removed, including CORBA see aforementioned link for specific details and complete list.

  • Reflection: reflection should be done via StackWalker rather than sun.Reflect, which was removed. JDK still has java.base/jdk/internal/reflect/Reflection, but set as internal inside a module named jdk.unsupported.

  • Deep reflection: user can add --add-opens flag at runtime option to make the code to access non-public members.

  • Like Java8, Java 11 has Long-term Support (LTS), in fact, the second LTS release after Java 8.

  • Java 11 has all the features of Java 10 and Java 9.

  • There are several features added to OpenJDK 11 (list below).

  • The boot class path has been mostly removed, ie. -Xbootclasspath and -Xbootclasspath/p options have been removed and only the -Xbootclasspath/a option was unaffected.

  • Illegal Access To Internal APIs: Non-public classes as well as classes from non-exported packages are inaccessible from outside the module and in case of access, a warning is emitted:

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by example.class
	(file:...) to field com.example.class.field

Main features added on Java 11:

  • Running Java File with a single command: no need to do javac.
  • New utility methods in String class
  • Local-Variable Syntax for Lambda Parameters
  • Nested Based Access Control
  • JEP 321: HTTP Client
  • Reading/Writing Strings to and from the Files
  • JEP 328: Flight Recorder
  • JEP 318: Epsilon
  • JEP 320: Remove the Java EE and CORBA Modules
  • JEP 329: ChaCha20 and Poly1305 Cryptographic Algorithms
  • JEP 315: Improve Aarch64 Intrinsics
  • Shenandoah/ZGC Garbage Collector (Experimental)
  • JEP 335: Deprecate the Nashorn JavaScript Engine

To see the complete list of features: Content from www.oracle.com is not included.JDK 11 Release Notes and/or Content from www.oracle.com is not included.Consolidated JDK 11 Release Notes.

Migration Guide


See the [JDK 11 - Migration Guide](https://docs.oracle.com/en/java/javase/11/migrate/migration-guide.pdf) for more information on the migration to JDK 11.

Diagnostic Steps

For InaccessibleObjectException in a certain package, just add one more --add-opens, example:

For access of private methods without the access:

java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @11222

Add: 

--add-opens java.base/java.lang=ALL-UNNAMED
--add-opens=java.base/java.util=ALL-UNNAMED
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