Problem when changing item pickup

Here I have a very simple event:

Code:

@EventHandler (priority = EventPriority.HIGHEST)
public void playerPickupItemOnServer (PlayerPickupItemEvent event) {
   
    ItemStack is = event.getItem().getItemStack();
    is.setAmount(16);
    event.getItem().setItemStack(is);
   
    System.out.println("ItemStack Amount: " + event.getItem().getItemStack().getAmount());
   
}

Whenever I pickup an item, this shows in console: (as expected)

ItemStack Amount: 16

However, the item's amount doesn't change.
Also, changing the type of the item doesn't work.

I must be missing something, any help is appreciated!

 

@nathanthesnooper
is this line needed?

event.getItem().setItemStack(is);

can't you just do event.getItem().getItemStack().setAmount(16);

 

that line is needed indeed.
looking into nms code and you'll find that getItemStack() method return a copy of related item snapshot.

Code:

public ItemStack getItemStack() {
    return CraftItemStack.asCraftMirror(this.item.getItemStack());
}

so you can't modify amount directly, need to set again.
but what's weird is that setItemStack() doesn't work. I've tested it, whatever you set, there always comes out
ItemStack{AIR x 0}
well, no further clue...consider to cancel that event and add items to player's inventory directly

 

I really don't know what u wanna do but I tried to do what I think u wanna do and ye..
Here is the code. Maybe that helps. (?)
If there are some problems just reply.

Code:

@EventHandler
    public void onPlayerPickupitem(PlayerPickupItemEvent e) {
        Player p = e.getPlayer();
       
        ItemStack i = e.getItem().getItemStack();
        i.setAmount(16);
       
        System.out.println("ItemStack Amount: " + e.getItem().getItemStack().getAmount());
       
        e.setCancelled(true);
        e.getItem().remove();
        p.getInventory().addItem(i);
        Bukkit.getWorld("world").playSound(p.getLocation(), Sound.ITEM_PICKUP, 1F, 1F);
    }