Consider the following code:

 

List<ItemStack> potion_subtypes = new ArrayList<ItemStack>();

Items.potionitem.getSubItems(Items.potionitem, null, potion_subtypes);

for (ItemStack is : potion_subtypes)
{
    System.out.println(is.getUnlocalizedName() + " =>" + is.getDisplayName());
}

 

It prints the following:

 

item.potion =>Water Bottle
item.potion =>Potion of Regeneration
item.potion =>Potion of Regeneration
item.potion =>Potion of Regeneration
item.potion =>Splash Potion of Regeneration
item.potion =>Splash Potion of Regeneration
item.potion =>Splash Potion of Regeneration
item.potion =>Potion of Swiftness
item.potion =>Potion of Swiftness
item.potion =>Potion of Swiftness
item.potion =>Splash Potion of Swiftness
item.potion =>Splash Potion of Swiftness
item.potion =>Splash Potion of Swiftness
item.potion =>Potion of Fire Resistance
item.potion =>Potion of Fire Resistance
item.potion =>Splash Potion of Fire Resistance
item.potion =>Splash Potion of Fire Resistance
item.potion =>Potion of Poison
item.potion =>Potion of Poison
item.potion =>Potion of Poison
item.potion =>Splash Potion of Poison
item.potion =>Splash Potion of Poison
item.potion =>Splash Potion of Poison
item.potion =>Potion of Healing
item.potion =>Potion of Healing
item.potion =>Splash Potion of Healing
item.potion =>Splash Potion of Healing
item.potion =>Potion of Night Vision
item.potion =>Potion of Night Vision
item.potion =>Splash Potion of Night Vision
item.potion =>Splash Potion of Night Vision
item.potion =>Potion of Weakness
item.potion =>Potion of Weakness
item.potion =>Splash Potion of Weakness
item.potion =>Splash Potion of Weakness
item.potion =>Potion of Strength
item.potion =>Potion of Strength
item.potion =>Potion of Strength
item.potion =>Splash Potion of Strength
item.potion =>Splash Potion of Strength
item.potion =>Splash Potion of Strength
item.potion =>Potion of Slowness
item.potion =>Potion of Slowness
item.potion =>Splash Potion of Slowness
item.potion =>Splash Potion of Slowness
item.potion =>Potion of Harming
item.potion =>Potion of Harming
item.potion =>Splash Potion of Harming
item.potion =>Splash Potion of Harming
item.potion =>Potion of Water Breathing
item.potion =>Potion of Water Breathing
item.potion =>Splash Potion of Water Breathing
item.potion =>Splash Potion of Water Breathing
item.potion =>Potion of Invisibility
item.potion =>Potion of Invisibility
item.potion =>Splash Potion of Invisibility
item.potion =>Splash Potion of Invisibility

 

How come awkward potions, mundane potions and clear potions aren't listed? How do I get a list of the subtypes that include those? Also, how do I get a list of the potions' crafting recipes?

subtypes for potions are computed and cached when asked for. Then only the effective potions (those with a list of effects) actually get returned. Awkward, mundane, milky, stinky, etc. etc. are not effective and therefore not sub-listed.

Those other names are seemingly random based on whatever potion id (damage value) is requested.

Tip: Study net.minecraft.potion.PotionHelper to discover why.

That's going to be a bit of a problem because I want to get all the potions and their recipes even if they're not really used.

 

I don't see what I'm supposed to be seeing in PotionHelper.

It's all right there. It is very complicated, so I don't imagine a beginner will understand how it works. Sorry I cannot spell it out for you.