How can you protect/encrypt your Java classes?

Question

Some time ago, in my work I needed to protect some classes against other people to read the code. For that purpose, I created a EncryptedClassLoader, that loaded previously

Answer 1

Short answer, you can't. Encryption doesn't work. Here's an oldish article about why it's pointless to use an encrypted class loader:

Unfortunately, you would be wrong, both in thinking that you were the first to come up with this idea and in thinking that it actually works. And the reason has nothing to do with the strength of your encryption scheme.

You can obfuscate it, but that will only go so far, and in the end I'm a firm believer that your time would be better spend fixing bugs or adding features.