What are the rev00000.dat files? I've created an application with bitcoinj that extracts all addresses which have been used out of the block chain files created by bitcoin-core.

I'm extracting the transactions only out of the blk*.dat files. Do these files really contain any transactions or are there further transaction in the rev*.dat files?

What does the rev*.dat files contain?
They are files to assist reversing additions to the blockchain, handling reorganisations. They essentially contain the references needed to quickly reverse a block being accepted and it’s changes being made to the nodes UTXO. It does not contain transactions.