Question: I added apache commons library jar file and javadoc.jar file in the Eclipse by following this article: <http://www.newthinktank.com/2012/01/how-to-install-java-libraries/>. I can use the library but when I type in the code the documentation doesn't show up. How can I fix this?

Answer: 
You don't add the `*-javadoc.jar` and the `*-sources.jar` to the classpath, and you likely don't need `*-tests.jar`.

Just add `commons-lang3-3.1.jar` to the classpath. Then, on the "Libraries" tab, click on the expand triangle.

Double-click "Source attachment", select "External location", click "External File..." and select the `commons-lang3-3.1-sources.jar` file. Click "OK".

Double-click "Javadoc location", select "Javadoc in archive" and "External File", click "Browse..." and select the `commons-lang3-3.1-javadoc.jar` file. Click "OK".
Restart Eclipse and if documentation is still not there then restart computer.