If I want to make a Chest that has 9 Slots for certain items reserved and 18 Slots for other items reserved, how would I go on to tell the Chest which item to fill in which slot, I have read through the Furnace and Chest TileEntity but that doesnt seem to help me with my core problem. Would I even tell the chest in the TE which item to accept for which slot or in the Container? And would I need to define the slots like in the FurnaceTileEntity (like 9 slots for x and 18 for y) or should I just define all 27 slots in one go and just check every item if it can be accepted for every slot? 

Just a bump into the right direction would help me already

Thanks in advance!

That depends on how you're "reserving" the items. One thing you could do is create a custom Slot class which extends Slot (for instance, you could call it ReservedSlot) which does nothing different except overrides isItemValid() to check whatever you need to check for reservations. Maybe even implements a separate isItemValid() method which takes other information, such as the slot index.

Shouldn't I use isItemValidForSlot then from IInventory in .net.minecraft.inventory? Because it says I should use Slot.isItemValid in the gui. Or should I let it check in the gui instead then?

Ahh thank you all for the hints, will check em out. I think I have better insight now on this topic
Edit: What is that boolean simulate doing in insertItem?

Edited November 27, 20177 yr by EvilTwin
Extra Question

5 hours ago, EvilTwin said:

Ahh thank you all for the hints, will check em out. I think I have better insight now on this topic
Edit: What is that boolean simulate doing in insertItem?

It's....simulating the insert. If true, the item will not actually be inserted, but the return value will be the same as if it had.

It's the "does this fit?" check.