How to Include JAR Files in Your Project Build Path in Eclipse

1. Locate your project in the Project Explorer. Right-click on the top-level folder of the project and select 'Properties.' The Properties pop-up window opens.

2. Click on 'Java Build Path' on the left side of the Properties window.

3. Verify that the JAR files you want to include in your classpath are in a directory under your Java project's structure. Normally, this is a folder named 'lib.'

4. Click on 'Add JARs' in the Properties window. If the JAR files are not in your project, click instead on 'Add External JARs.' Navigate to the folder in your project containing the JARs that you want to add to the build path. Select the JAR files and click 'OK.'

5. Click 'OK' in the Properties window to close it. The JAR files have been added to your class path and any ClassNotFoundException errors in your application associated with these JAR files will be eliminated.