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I have installed Java 1.8 from Oracle on Ubuntu because I though it would be best, newest version compatible with previous ones. But it is not. javac 1.8 produces bytecode runnable only on the java-8-oracle, scala does not run.

Before upgrade I was using java-7-openjdk, everything was fine. While I can choose my older virtual machine using sudo update-alternatives --config java, but I also need to be able to choose older compiler. How can I do this?

the
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Vaidotas
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3 Answers3

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Use the -target flag to generate bytecode for earlier version. E.g. javac -target 1.5 FooBar.java.

There's no need to downgrade.

Kayaman
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  • Your suggestion gives "javac: target release 1.7 conflicts with default source release 1.8". – Vaidotas Apr 27 '14 at 10:19
  • Then modify the source compatibility as well with `-source 1.7`. – Kayaman Apr 27 '14 at 10:19
  • Better, but I still get "warning: [options] bootstrap class path not set in conjunction with -source 1.7". But at least I can launch programs now, thanks. – Vaidotas Apr 27 '14 at 10:21
  • Note that this won't prevent you from using APIs only available in Java SE 8. You would need some additional steps: http://docs.oracle.com/javase/8/docs/technotes/tools/unix/javac.html#BHCIJIEG For this reason I recommend to use the JDK you're actually targeting. – Puce Apr 27 '14 at 10:33
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At least for Oracle's JDK (not sure about OpenJDK): install either the oracle-java7-set-default or the oracle-java8-set-default package, depending on which java version you want to be the default on your system.

You can get it from: http://ppa.launchpad.net/webupd8team/java/ubuntu (including the actual Oracle JDKs) See: https://launchpad.net/~webupd8team/+archive/java

Alternatively you could set the PATH and JAVA_HOME environment variables e.g. in /etc/environment

That said, when you compile you could specify the source and target level to 1.7, which would generate Java SE 7 compatible bytecode also when using JDK 8. But note it won't check if you're using some API not available in Java SE 7.

For this reason I recommend to use always the JDK version you target rather than doing some cross-compiling (which would need some additional extra steps to do it right).

Note however that you can install several JDK versions on your systems. IDEs usually let you choose which one you want to use during development.

Puce
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  1. Set up java_home environment variable to older version and compile Java files using it. Make sure that java.exe in path variable is of earlier version.

  2. Use -target flag while compiling.

RoadieRich
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Anand Kulkarni
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