Guys guys guys.
Stop confusing him.
Like pirulo259 said, use getItemAttributeModifiers().
BUT BE SURE TO CREATE A NEW HASHMAP, NOT THE ONE ItemSword USES!!!!
It should be this:
public Multimap getItemAttributeModifiers()
{
Multimap multimap = HashMultimap.create(); // this part, you need to create a new hash-multimap!
multimap.put(SharedMonsterAttributes.attackDamage.getAttributeUnlocalizedName(), new AttributeModifier(field_111210_e, "Weapon modifier", (double)this.field_150934_a, 0));
return multimap;
}