Java anti-hacking. How protect .class file from being changed in my jar

Question

I'm creating a sotware and will distribute it as trial to users test It. But if someone unpack my jar and change the bytecode of my licensing classes this guy will be able to create a crack to my software. There is any way to check the hash of my .class files and ensure that everything is ok with it? What are the best ways to protect my software from being hacked?

Answer 1

It can't be done, at best you can slow down the person trying to crack it. Your time is probably better put to developing a great product and ignore people that pirate it.

Answer 2

You could probably sign your JAR files as shown here. However, that being said, one usually looses control over their own software the moment they hand it over to their client.