How do I give items or armor an attribute modifier. I want to make armor that gives you extra hearts. How would I do this

override

getAttributeModifiers(EquipmentSlotType slot, ItemStack stack)

and then you can add new attributes to the multimap get from calling 

super.getAttributeModifiers(slot, stack)

here's an example

        Multimap<String, AttributeModifier> multimap = super.getAttributeModifiers(slot, stack);
        if (slot == EquipmentSlotType.MAINHAND)
            multimap.put(SharedMonsterAttributes.ATTACK_SPEED.getName(), new AttributeModifier(ATTACK_SPEED_MODIFIER, "Weapon modifier", Integer.MAX_VALUE, AttributeModifier.Operation.ADDITION));

you can check vanilla sword for examples

Thanks for the help. 🙂