The Java Test Tool requires Java 8 to be installed to work correctly. A lot of people (including ourselves) have had trouble running the app, even after downloading and installing the latest Java 8 JDK.

Common problems

hfortier$ ./exampleapp
Exception in thread "main" java.lang.UnsupportedClassVersionError: com/gambit/sdk/example/GambitExample : Unsupported major.minor version 52.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
	at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:482)

This means your Java version is out of date. Try running $ java -version:

hfortier$ java -version
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)

Yup. You need 1.8.x

1. Go to System Preferences
2. Click on Java
3. In the Java Control Panel, click on the Update tab.
4. Make sure you have updated to 1.8.x, if you haven't do so now.

If you have updated to 1.8.x as per what is being reported by the Java Control Panel, then see the appropriate section for your OS listed below:

OSX Trouble?

Please note that Apple / Oracle both don't play well and as a result, even "upgrading" your OSX Java version still will not affect which version of Java your terminal is running. Even after I updated to 1.8.x, my terminal still showed this:

hfortier$ java -version
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 you are completely positive that you have the latest Java installed as per prior instructions, then you should be able to run:

sudo rm /usr/bin/java
sudo ln -s /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java /usr/bin

Which should fix the problem. This is because on OSX java is usually located in /usr/bin/java. But the Oracle Java Updater installs it to /Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java

So by fixing the symlink at /usr/bin/java to point to the new version - problem solved!

hfortier$ java -version
java version "1.8.0_73"
Java(TM) SE Runtime Environment (build 1.8.0_73-b02)
Java HotSpot(TM) 64-Bit Server VM (build 25.73-b02, mixed mode)

Windows problems?

After installing JDK 8 and running java -version, it shows the correct version, but the app still throws exceptions on launch.

This is likely because your JAVA_HOME environment variable is still pointed to the old version of Java. 

1. Right click My Computer and select Properties.
2. On the Advanced tab, select Environment Variables, and then edit JAVA_HOME to point to where the JDK software is located, for example, C:\Program Files\Java\jdk1.8.0_44.