ItemStack

This is the vanilla ItemStack. It is recommended that you use IItemStack whenever possible

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import at the very top of the file.

import crafttweaker.api.item.ItemStack;

ItemStack.asIIngredient() as IIngredient
myItemStack.asIIngredient();

ItemStack.asIItemStack() as IItemStack
myItemStack.asIItemStack();

ItemStack.print() as void
myItemStack.print();