Executing a .class file on Mac OS X 10.48

Hello, I downloaded a free applet with .class extension, but when I double click it, it won't open the file or execute it. I have the latest version of Java already installed from java.com and the console reads the following:

Exception in thread "main" java.lang.NoClassDefFoundError: com/instill/xActionListener

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClass(ClassLoader.java:620)

at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)

at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)

at java.net.URLClassLoader.access$100(URLClassLoader.java:56)

at java.net.URLClassLoader$1.run(URLClassLoader.java:195)

at java.security.AccessController.doPrivileged(Native Method)

at java.net.URLClassLoader.findClass(URLClassLoader.java:188)

at java.lang.ClassLoader.loadClass(ClassLoader.java:306)

at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)

at java.lang.ClassLoader.loadClass(ClassLoader.java:251)

at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)

[1137 byte] By [newbie38a] at [2007-11-27 11:27:41]
# 1

Exception in thread "main" java.lang.NoClassDefFoundError: com/instill/xActionListener

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClass(ClassLoader.java:620)

at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)

at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)

at java.net.URLClassLoader.access$100(URLClassLoader.java:56)

at java.net.URLClassLoader$1.run(URLClassLoader.java:195)

at java.security.AccessController.doPrivileged(Native Method)

at java.net.URLClassLoader.findClass(URLClassLoader.java:188)

at java.lang.ClassLoader.loadClass(ClassLoader.java:306)

at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)

at java.lang.ClassLoader.loadClass(ClassLoader.java:251)

at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)

newbie38a at 2007-7-29 16:17:36 > top of Java-index,Java Essentials,New To Java...