Compress List of ItemStack

CompressListOfItemStack.java

import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.HashMap;

import org.bukkit.Material;
import org.bukkit.inventory.ItemStack;

/*
Will return a new ArrayList, without modifying the original List
Does not account for tools or nbt data. Too bad!
*/
public static ArrayList<ItemStack> compressedList(List<ItemStack> itemStacks) {
    HashMap<Material, int> materials = new HashMap<Material, int>(){{
        for (ItemStack itemStack: itemStacks) {
            if (itemStack != null) {
                int i = get(itemStack.getType());  // can be null
                put(itemStack.getType(), i == null ? itemStack.getAmount() : itemStack.getAmount() + i);
            }
        }
    }};
    
    return new ArrayList<ItemStack>(){{
        for (Map.Entry<Material, int> entry: materials.entrySet()) {
            Material m = entry.getKey();
            int count = entry.getValue();
            while (count >= 64) {
                add(new ItemStack(m, 64));
                count -= 64;    
            }
            add(new ItemStack(m, count));
        }
    }};
}