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_76/bin/java                        100       manual mode
* 2            /opt/jdk1.8.0_25/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:

ArchLinux

A bit drastic but you can use this script to change the symbolic links

#!/bin/bash
# This script iterates all symlinks in the BIN_DIR directory that have the same JDK path as 'java'
# and replaces every symlink with a new one that has the JDK path set from the first script argument.
#
# Useful if you want to switch symlinks from OpenJDK to any other JDK.
# E.g. ./replace-java-symlinks.sh /opt/java6
#
# author: Zdenek Obst, zdenek.obst-at-gmail.com

BIN_DIR=/usr/bin

if [[ $EUID -ne 0 ]]; then
  echo "You must be root to run this script"
  exit
fi

if [[ -z "$1" ]]; then
  echo "Pass the new JDK home as the first argument, e.g. /opt/java6"
  exit
fi

ACTUAl_JDK_PATH=`ls -l $BIN_DIR/java | awk '{print $11}' | sed 's:\/jre\/bin\/java::g'`
echo "=> Actual JDK path used by symlinks is: $ACTUAl_JDK_PATH"

NEW_JDK_PATH=`echo ${1%/}` # remove last slash if needed
echo "=> New JDK path for symlinks will be: $NEW_JDK_PATH"

read -p "Are suggested JDK paths correct? (y/n) " yn
if [ "$yn" != "y" ]; then
  echo "Cancelled on user's request"
  exit
fi

echo "----------------------------------------------"

FILES=`ls -l $BIN_DIR | grep $ACTUAl_JDK_PATH`

ls -l $BIN_DIR | grep $ACTUAl_JDK_PATH | while read file;
do
  FILENAME=`echo $file | awk '{print $9}'`
  SYMLINK=`echo $file | awk '{print $11}'`
  
  ACT=`echo $ACTUAl_JDK_PATH | sed 's:\/:\\\/:g'` # escape characters for SED
  NEW=`echo $NEW_JDK_PATH | sed 's:\/:\\\/:g'` # escape characters for SED
  
  NEWLINK=`echo $SYMLINK | sed "s/$ACT/$NEW/g"`
  
  if [ -f $NEWLINK ]; then
    echo "-> Replacing symlink: $BIN_DIR/$FILENAME -> $NEWLINK"
    rm $BIN_DIR/$FILENAME
    ln -s  $NEWLINK $BIN_DIR/$FILENAME    
  else
    echo "!! File $NEWLINK does not exist, skipping symlink re-creation"
  fi
  
done

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, but depends on convention that home/bin trumps /usr/bin

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.

Using jEdit macro & commando files

bash macro

// rp5.bsh
//setenv("JAVA_HOME", "/opt/jdk1.7.0_51");
setenv("JAVA_HOME", "/opt/jdk1.8.0");
setenv("GEM_HOME", "/home/tux/.gem/ruby/2.2.0");
setenv("GEM_PATH", "/home/tux/.gem/ruby/2.2.0");
new console.commando.CommandoDialog(view,"commando.rp5");

jEdit commando file

<!-- Monkstone, 2013-August-16 for ruby-processing > 2.0.12 -->
<COMMANDO>
<UI>
<CAPTION LABEL="Run">
<FILE_ENTRY LABEL="ruby file" VARNAME="file" EVAL="buffer.getName()"/>
</CAPTION>
<CAPTION LABEL="Path to rp5">
<ENTRY LABEL="path" VARNAME="rp5path" DEFAULT=""/>
</CAPTION>
<CAPTION LABEL="Choose Run/Watch/Create/App">
<CHOICE LABEL="Select" VARNAME="type" DEFAULT="run" >
<OPTION  LABEL="run" VALUE="run"/>
<OPTION LABEL="watch" VALUE="watch"/>
<OPTION LABEL="create" VALUE="create"/>
<OPTION LABEL="export app" VALUE="app"/>
<OPTION LABEL="export applet" VALUE="applet"/>
</CHOICE>
</CAPTION>
<CAPTION LABEL="JRuby Opt">
<TOGGLE LABEL="jruby-complete" VARNAME="jruby" DEFAULT="FALSE"/>
</CAPTION>
</UI>

<COMMANDS>

<COMMAND SHELL="System" CONFIRM="FALSE">
<!-- cd to working dir -->

	  buf = new StringBuilder("cd ");
	  buf.append(MiscUtilities.getParentOfPath(buffer.getPath()));
	  buf.toString();
	
</COMMAND>



<COMMAND SHELL="System" CONFIRM="FALSE">

	  buf = new StringBuilder(rp5path);
	  buf.append("rp5 ");
	  if (jruby){
	  buf.append("--nojruby ");
	  }	 
	  buf.append(type);
	  buf.append(" "); 
	  switch(type){
	  case "run":
	  case "watch":
	      buf.append(file);
	      break;
	  }
	  buf.toString();
	
</COMMAND>


</COMMANDS>
</COMMANDO>

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)

Edit your .jrubyrc in $HOME (for global configuration, NB: jruby-complete may also pick up this configuration up, especially if you kick-off ruby-processing with an installed jruby), apparently you can also have a .jrubyrc in a local folder and that takes precedence.
Edit data/jruby_args.txt in your local folder -XX:+TieredCompilation on its own seems to work best.