Are there any anti-cheating frameworks for Java games in order to make it a bit harder to cheat? (eg. something that protects from things like Cheat-Engine) Obviously if the cheater were to develop his own tools this wouldn't help much, but I'm looking to protect the game from the average cheating 13 yr. old child.
None ready that I know of.
Commercial (expensive) systems like PunkBuster exist, which constantly scan memory locations for changes, asserting that they haven't changed by impossible amounts or at impossible moments in time.
You could implement something like this yourself, by occasionally asserting that the changes to the contents of your variables make sense.
If it's a singleplayer game you're working on, I have a very personal request: Please don't do it! Back when I was 13, I learnt a lot about how games work by CheatEngineering or Poking them. It's like taking apart toasters and RC cars. I want my kids to live in a world where they can choose to break their things regardless of the opinion of a grown-up who "knows better".