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I am using a MackBook Pro with Mac OS X 10.8.2. I currently have Java 6 installed:

wdb-laptop:~ wdb$ java -version
java version "1.6.0_37"
Java(TM) SE Runtime Environment (build 1.6.0_37-b06-434-11M3909)
Java HotSpot(TM) 64-Bit Server VM (build 20.12-b01-434, mixed mode)

I would like to install Java 7 to play with JavaFX, however, all of my apps for work are still on Java 6. So I would like to install Java 7 "on the side". Is his possible? If so, how? I want to make sure I will not loose my Java 6 installation if I run the .dmg from Oracle.

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The oracle Java 7 does not remove the Apple supplied Java 6. It does however change /usr/bin/java to start the Oracle Java.

To start a jar with Java 6 instead of just using java on the command line put in the full path to the java i.e. /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/bin/java

0

I had a similar situation at work, so I did a bit of research and, with a couple minutes of setup, it can be almost painless to switch back and forth between Java 6 and 7 (or 7 and 8, for that matter - this method is version agnostic).

For anyone with java installed, /usr/libexec/java_home will show the JAVA_HOME directory, but it's especially powerful when you have multiple versions of java installed side-by-side on OS X.

Using the -V flag, you can see all of the installed JVMs:

$ /usr/libexec/java_home -V
Matching Java Virtual Machines (3):
    1.7.0_67, x86_64:   "Java SE 7" /Library/Java/JavaVirtualMachines/jdk1.7.0_67.jdk/Contents/Home
    1.6.0_65-b14-466.1, x86_64: "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
    1.6.0_65-b14-466.1, i386:   "Java SE 6" /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home

You can also get the JAVA_HOME value for a specific JVM like this:

$ /usr/libexec/java_home -v 1.6
/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
$ /usr/libexec/java_home -v 1.7
/Library/Java/JavaVirtualMachines/jdk1.7.0_67.jdk/Contents/Home

Putting this all together, this is what I added to my ~/.profile:

## java home
alias j6="export JAVA_HOME=\$(/usr/libexec/java_home -v 1.6);echo 'using Java 6'"
alias j7="export JAVA_HOME=\$(/usr/libexec/java_home -v 1.7);echo 'using Java 7'"
## manual switch for 1.6 or 1.7
j6 ## enable java 6 (or just run j6 in terminal)
## j7 ## enable java 7 (or just run j7 in terminal)

So you can see that right now, my terminal defaults to Java6, but I can switch this by just typing j7 on the command line (or editing the ~/.profile):

$ java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-466.1, mixed mode)    
$ j7
using Java 7
$ java -version
java version "1.7.0_67"
Java(TM) SE Runtime Environment (build 1.7.0_67-b01)
Java HotSpot(TM) 64-Bit Server VM (build 24.65-b04, mixed mode)

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