J. W.

I know the code has probably changed a bit since May of 2014, but maybe that sample commented from then is still a possible solution for this near 4 year old problem?

The disposition of Mojang on this issue is that entity types of Mob and Monster returning "Entity type 'Mob/Monster' is invalid" is "Working as Intended"?

This wasn't a feature request. It was a report that two entity types listed in source code (in the static constructor of class EntityList; along with all the other entity names listed there that DO work) as being an aliased type of entity potentially usable by an entity selector appearing to not work.

I'll make a suggestion in /r/minecraftsuggestions if the official position is "Working as Intended", otherwise it's still a bug report (based on the source available in the Minecraft Mod Coder Pack).

Fields and fields of sheep. There are more even beyond the entity render distance.

6 chunks in close proximity to each other all spawned horses.

This is actually still an ongoing issue in 1.7.x.

I was travelling long distance (> 10km) and encountered several animal herds of all the same type.

Horses, for instance, have a weight of 5 in the Plains biome (thus having a 5 in 45 chance of being selected, yes??). However, when travelling as mentioned all new chunks I encountered at the time spawned horses.

I'm certain the issue is related to the millisecond resolution available to java.util.Random to use as a seed. With my own modding, java.security.Random adequately randomized the process WeightedRandom uses to select a WeightedRandomItem when called (rather than the process that deals with terrain generation). Of course, using java.security.Random means recreating a world with the same seed would mean mob spawns would be entirely random every time, but I think that may be an improvement to having to travel many kilometers to find something other than sheep (considering mutton does not exist {yet?}).

I will try to find the crazy horse spawns and add a screenshot.

I've just found the issue has more to do with the random numbers being rolled than with the entries in the biome creatures list.

Could it be the method used for picking random numbers relies on an internal mechanism that doesn't change as fast as code can call it?

In 1.6.2 I saw a lot of rolls of 11 which resulted in picking sheep a majority of the time. In 1.5.2, which I assumed was normal, I see lots of rolls for 16 which results in picking pigs most of the time.

Maybe <Random>.nextInt() needs to be replaced with something else?

Anyway, that's my discovery. Don't think I'll be doing any more research on the issue. Maybe Mojang and their far more experienced Javanauts know of something trivial that will solve the problem. 🙂

The spawn generation is the same under the 32-bit version of Java (too many sheep).
The spawn generation is the same in v1.6.1 (too many sheep).

The spawn generation is "normal" in 1.5.2; though in the attached screenshots of sheep all are replaced by pigs and sheep spawn frequently in the forest surrounding the spawn point.

I was just thinking...

Could this be an issue relating to the use of the 64-bit version of Java? Would that affect a random number generator and cause the roll of a particular number to be unusually high?