Hm... How does minecraft do it? I googled it, and nothing useful came up.
Here is what I think you want to do:
You have a bunch of different tiles your game can use, you want to create a Tile by its name. I.e, you want to create com.wesley.laferriere.world.SandTile by its name, and com.wesley.laferriere.world.GrassTile from its name. This way, when you want you save your map, you can say: These tiles are SandTile, and these tiles are GrassTile, then when you load your map you can just load all the tile's classes with their name.
If that sounds like what you want to do, just say and I have a few routes you can take.