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On execution of ModelGUI, you may encounter the following exception:

Unsupported major.minor version 51.0

This basically means the version of Java that runs by default on your system (i.e., the one which is called by typing "java" in the terminal) is outdated. To see what version is currently the default on your system, type:

java -version

You should see something like:

java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)

If the version is 1.6.blah, this problem can be solved by updating your Java version to 1.7 or later. If you have already done so and are still getting the error, see below.

To update Java on Ubuntu, type:

sudo apt-get update
sudo apt-get install openjdk-7-jdk

This will install OpenJDK. If you prefer Oracle's JDK, follow the instructions here instead.

To update on other systems, go here (preferred) or here and follow the instructions for your particular system.

I've installed 1.7 but it is not the default

If you have already upgraded Java, but you still get the major.minor error, the problem is probably that the default version is not pointing to it.

For Ubuntu, you can fix this with the command below:

sudo update-alternatives --config java

Which will give a list similar to that shown below (but with 1.6 selected), that will allow you to specify which version of Java runs by default:

There are 2 choices for the alternative java (providing /usr/bin/java).

Selection    Path                                            Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-7-oracle/jre/bin/java          1062      auto mode
  1            /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   1061      manual mode
  2            /usr/lib/jvm/java-7-oracle/jre/bin/java          1062      manual mode

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

For Windows and Mac, the latest installed version should be set to default. If you have trouble with this, you will need to find the path to the latest version and add this to the front of your PATH environment variable OR in the command line of the ModelGUI executable itself.