I'm going to take Paul's advice one further. There are some great tools for this.
The schemaspy utility can scan a database schema and render it with graphical documentation. It can produced a hyperlinked website of the schema, and also, if memory serves, several other forms, such as PDFs
You can get a class overview using the reverse engineering features of tools like ArgoUML. The downside to UML charting being that it has no sense of proportion so you end up with acres of paper where the most trivial classes are indistinguishable from the most critical ones.
And, last, but not least, run JavaDoc! Applications that have fully leveraged JavaDoc's abilities can make a complete illustrated technical manual out of a program's source code, but even poorly-documented apps can at least be outlined.
Note also that if you're in a continous-integration shop, tools like
Jenkins can run these documentation apps as part of the build process and display the results as part of the Jenkins dashboard.
Some people, when well-known sources tell them that fire will burn them, don't put their hands in the fire.
Some people, being skeptical, will put their hands in the fire, get burned, and learn not to put their hands in the fire.
And some people, believing that they know better than well-known sources, will claim it's a lie, put their hands in the fire, and continue to scream it's a lie even as their hands burn down to charred stumps.