steps to download and add the "com.mysql.jdbc.Driver" connector j to NetBeans IDE:

1. Go to the MySQL website and download the connector j. Make sure you download the version that is compatible with your version of MySQL and your operating system. You can do this by navigating to the following link: https://dev.mysql.com/downloads/connector/j/

2. Once you have downloaded the connector j, extract the downloaded file to a folder on your computer. You can do this by right-clicking on the downloaded file and selecting "Extract All" or by using a file archiver such as WinZip or 7-Zip.

3. Open NetBeans IDE and either create a new Java project or open an existing project that you want to use the connector j with.

4. In the Projects window, right-click on the project and select Properties. This will open the Project Properties dialog box.

5. In the Project Properties dialog box, click on the Libraries category. This will display the libraries that are currently associated with the project.

6. Click on the Add JAR/Folder button to add the connector j to the project. This will open the Add Library dialog box.

7. In the Add Library dialog box, navigate to the folder where you extracted the connector j and select the "mysql-connector-java-x.x.x.jar" file. This file contains the "com.mysql.jdbc.Driver" class that you need to connect to a MySQL database.

8. Click Open to add the connector j to the project. This will associate the connector j with your project and enable you to use the "com.mysql.jdbc.Driver" class in your code.

9. In the Project Properties dialog box, click OK to save the changes. This will close the dialog box and return you to the main NetBeans IDE window.

10. You can now use the "com.mysql.jdbc.Driver" class in your Java code to connect to a MySQL database. To do this, you will need to import the class into your code and use it to create a connection to your MySQL database.

When the driver class "com.mysql.jdbc.Driver" is not found, the Java runtime environment throws the "java.lang.ClassNotFoundException com.mysql.jdbc.Driver" exception. This can happen due to various reasons, such as the driver not being in the classpath, the JAR file being in an incorrect location, or incorrect class name. To resolve the issue, the driver class must be added to the classpath, and the correct class name should be used.

That's it! You have successfully downloaded and added the "com.mysql.jdbc.Driver" connector j to your NetBeans IDE project. This will allow you to connect to a MySQL database and use it in your Java application.