Experimenting with jdk8

Debian linux

If you are on any variant of Debian linux (Mint / Ubuntu etc), there is the convenience of being able to set alternative java using update-alternatives:-

su -c "update-alternatives --config java"

or

sudo update-alternatives --config java

Output

There are 3 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      auto mode
  1            /opt/jdk1.7.0_51/bin/java                        100       manual mode
* 2            /opt/jdk1.8.0/bin/java                           100       manual mode
  3            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      manual mode

Press enter to keep the current choice[*], or type selection number: 

Other linux

Simple but crude, ensure you have a user bin folder (and that it is on your PATH) create a bash script as follows,

#!/usr/bin/env bash
export JAVA_HOME="/opt/jdk1.8.0"
${JAVA_HOME}/bin/java $@

and make it executable chmod +x bin/java

Windows

some nice person will edit this? Setting JAVA_HOME might do it.

MacOSX

some nice person with a rollneck sweater will edit this? Setting JAVA_HOME might do it.

Tools/Configuration

How do I check which version of the JVM JRuby is running on?

jruby -rjava -e "puts java.lang.System.get_property('java.version')"

prints out 1.8.0 with above setup.

How do I optimise performance (make use of jvm flags)

1. Edit your .bashrc (for global configuration, NB: jruby-complete may also pick up this configuration up, especially if you kick-off ruby-processing with an installed jruby) -XX:+TieredCompilation on its own seems to work best.

2. Edit data/jruby_args.txt in your local folder