OpenJDK 8 or OpenJDK 9 for AOSP 10: which one?

[John W. Blue]

Hello,

 

I read here:

 

https://android.googlesource.com/platform/build/+/refs/tags/android-10.0.0_r6/core/java_common.mk

 

# TODO(ccross): allow 1.9 for current and unbundled once we have SDK system modules

    LOCAL_JAVA_LANGUAGE_VERSION := 1.8

  else

# DEFAULT_JAVA_LANGUAGE_VERSION is 1.8, unless TARGET_OPENJDK9 in which case it is 1.9

 

So is OpenJDK 8 the recommended version or is OpenJDK 9?  And is java_common.mk file the only way to tell?

 

John

[Colin Cross]

The source for Android 10 includes prebuilt java toolchains used for compiling the platform in prebuilts/jdk/jdk8 and prebuilts/jdk/jdk9, so there should be no need to provide any OpenJDK version.

The platform always uses javac from OpenJDK9 to compile (prebuilts/jdk/jdk9/linux-x86/bin/javac), OpenJDK8 is EOL upstream.    Those comments are about selecting what language features are being targeted by the OpenJDK 9 toolchain.  In Android 10, we default to passing -source 1.8 -target 1.8 to javac to target OpenJDK8 language features, unless you set EXPERIMENTAL_USE_OPENJDK9=true on the command line, which will default to passing -source 1.9 -target 1.9.  There is no reason to do this in Android 10, as there is no platform support for Java language 9 features.  In master you can use EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9=true to get the same effect.

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[Colin Cross]

Correction, EXPERIMENTAL_JAVA_LANUAGE_LEVEL_9=true is the default in master, and is moving to required with https://android-review.googlesource.com/c/platform/build/soong/+/1151196.