Example:  You have a class named "Set" in a project folder "e:\myProject" and package named com.zxy.client, will you be able to compile and execute it as it is

package com.xyz.client;

public class Pet {

public static void main(String[] args) {

System.out.println("I am found in the classpath");

}

}

To run-> e:\myProject> java com.zxy.client.Set

The answer is no and you would get the following exception: "Exception in thread "main" java.lang.- NoClassDefFoundError: com/zxy/client/Set". You have to set the classpath. How shall you do that? One of the following ways:

1. Set the operating system CLASSPATH environment variable to have the project folder "e:\myProject".

2. Set the operating system CLASSPATH environment variable to have a jar file "e:/myProject/client.jar", which has the Set.class file in it.

3. Run it with -classpath or -cp option as given below:

c:\>java -cp c:/myProject com.xyz.client.Pet

OR

c:\>java -classpath c:/myProject/client.jar com.xyz.client.Pet