How to fix "Exception in thread "main" java.lang.NoClassDefFoundError:org/antlr/Too"

The following error is an initial error for ANTLR developers, when they try to build their application for the first time using command prompt:

What you need to do?

You need to set the Java Classpath for ANTLR application as given below in cmd:
set CLASSPATH = D:\antlr\antlr-3.1.3.jar

Check if it is set correctly using the following command:
echo %CLASSPATH%

Above command should display the given path.

Then verify it using the following command:
java org.antlr.Tool -version

The result should be something like this based on your ANTLR version:
ANTLR Parser Generator Version 3.1.3 Mar.18 2009 10:09:25

Why you need to do that?

The Classpath is a parameter set either command line or through envronment variable that tells JVM (Java Virtual Machine) where to look for user defined classes and packages when running Java programs. Without this, JVM does not know where to fine code base related to org.antlr.Tool.