Modify Hostile Mob Spawn

[Mctittles]

So, all I'm looking to do is for the player to be able to specify a block or blocks and those blocks will not spawn hostile mobs on them.

 

Been looking through the code and forums but really I don't know where to start.  Is this possible?  Can I modify the existing minecraft class or is there another way?

 

Thanks!

[Eternaldoom]

You might be able to use an EntityJoinWorldEvent and cancel it if the entity is above your block. You can't modify existing classes (other than using ASM), and you shouldn't need to.

[Mctittles]

Thanks for the help guys; both of these look like they will work great!