JAVAC not recognised as an internal or external command

After installing the Java SE Development Kit 6, I created a java application, and when to the command prompt to compile it, I got this error message: 
"JAVAC not recognised as an internal or external command"


I eventually found JAVAC.exe by browsing to this folder:
C:\Program Files\Java\jdk1.6.0_23\bin


There are two ways to avoid the error message:
1) Supply the full path to JAVA.exe when compiling
2) Add an environment variable to this path.


In windows vista this can be found in Control Panel\System\Advanced System Settings
There is a button here for Environment Variables, as shown in the screen shot:

In the system variables, look for one called path and edit it
In the variable value box go to the end, add a semi-colon and the path to the JAVAC folder, eg ; C:\Program Files\Java\jdk1.6.0_23\bin\


Once compiled and executing the class from the command prompt you may still get errors such as this:

Exception in thread "main" java.lang.NoClassDefFoundError: YourAppName(wrong
name: YourAppName)

1. Two things to bear in mind, when using JAVA to execute the class, do not add the .Class suffix to the class name when executing.
2. Everything is case sensitive. Make sure the name of the class you enter matches the actual name in case as well as spelling