How would I put and obtain the values within hashmap.  It always returns null?

 

class 1

public static HashMap<ItemStack, Integer> Levels = new HashMap(200)
...//code
ItemStack stack = new ItemStack(Blocks.stone);
Levels.put(stack, 5)

 

class2

ItemStack stack = new ItemStack(Blocks.stone);
int requiredLevel = Levels.get(stack)//Is Null

 

 

ItemStack

doesn't override the

hashCode

method, so two instances are treated as different keys even if they share the same contents.

 

To use an

ItemStack

as a key, you'll need a wrapper class that overrides

hashCode

to return the hash code of the

ItemStack

's contents;

com.google.common.base.Objects#hashCode

will combine the hash codes of multiple objects for you.

 

Exactly which parts of the

ItemStack

you use in the hash code depends on your requirements: Do you only care about the

Item

, stack size and metadata; or do you include the NBT as well?

NBTTagCompound

overrides

hashCode

to return the hash of its contents, so you don't need to calculate that yourself.

also, if you'll only need to differentiate between item, stack size and metadata, and if you won't need to put or get things into the map too often then you could put/get ItemStack.toString. I think it would work, but it's probably slow.

Thank you for the replies.  I will probably create a wrapper class that holds the item, stack size(Maybe), and metadata and override hashcode.

If you don't want to use a wrapper class you can also use a TCustomHashMap from the trove library (Minecraft comes with it). This lets you specifiy how to calculate equals and hashCode instead of using the normal methods.

 

While I will probably just use wrapper objects, that's pretty neat.