How do I use "itemInteractionForEntity"?

[Netglex]

Hello together. I have the following question: How do I use itemInteractionForEntity(ItemStack par1ItemStack, EntityLiving par2EntityLiving)? There were two arguments: Objects of ItemStack and EntitiyLiving. Now I want to get a certain item, if I click on an animal. This looks like this:

@Override
public boolean itemInteractionForEntity(ItemStack par1ItemStack, EntityLiving par2EntityLiving)
{
	if (this.isFull == 0 && par2EntityLiving instanceof EntityOcelot {
		par1ItemStack = new ItemStack(Tutorial.FishBone);
	}	
	return true;
}

But obviously the item won't change. I've already tried with itemID, itemID+256, itemID-256, but all these didn't work. What do I have to improve? And what is the return-value standing for?

[thebest108]

par1ItemStack.Id = somethingElse +256;

Also, is this.isFull just a standard Boolean, because that would cause multiplayer issues

[Netglex]

Thanks so far, but I can't use par1ItemStack.Id. Id is simply not available. And sorry, if I was unprecise: This is the right code: without this.isFull (this.isFull was copied from a bucket and this.isFull means the bucket's content):

@Override
public boolean itemInteractionForEntity(ItemStack par1ItemStack, EntityLiving par2EntityLiving)
{
	if (par2EntityLiving instanceof EntityOcelot {
		par1ItemStack.itemID =Tutorial.itemID+256;
	}	
	return true;
}

But anyway: How do I solve this problem now? And what does the return-value mean?