getItemMeta is always returning null in my spigot plugin-CodePudding

Hi fellow coders I have been trying to make a custom sword and put it into a shop gui but when I try to change the swords meta using ItemStack.getitemmeta() and then i try to set the display name or something it says the sword meta is null. Also I am changing My actual name in irl to my name and the server name to server name

Error:

Caused by: java.lang.NullPointerException: Cannot invoke "org.bukkit.inventory.meta.ItemMeta.setDisplayName(String)" because "weaponMeta" is null

Blunt Knife.java

package me.myname.servername.items.weapons;

import me.myname.servername.Utils.Weapon;
import org.bukkit.Material;
import org.bukkit.inventory.ItemStack;

import java.util.ArrayList;

public class BluntKnife extends Weapon
{

    public void BluntKnife()
    {
        tradable = true;
        damage = 12;
        rarity = "COMMON";
        name = "Blunt Knife";
        ArrayList<String> lore = new ArrayList<String>();
        lore.add("Damage:  12");
        lore.add("");
        lore.add("Can be upgraded with /upgrade for 500 coins!");
        lore.add("");
        lore.add("⚔ COMMON SWORD ⚔");
        item = new ItemStack(Material.AIR, 1);

    }
}

MakeItem.java

package me.myname.servername.Utils;

import org.bukkit.Bukkit;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;

public interface MakeItem
{
    public default ItemStack makeItemFromWeapon(Weapon wpn)
    {
        ItemStack weapon = wpn.item;
        ItemMeta weaponMeta = weapon.getItemMeta();

        weaponMeta.setDisplayName(wpn.name);
        weaponMeta.setLore(wpn.lore);
        weapon.setItemMeta(weaponMeta);
        
        return weapon;
    }
}

Weapon.java

package me.myname.servername.Utils;

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

import java.util.ArrayList;

public class Weapon
{
    protected boolean tradable = true;
    protected int damage = 5;
    protected String rarity = null;
    protected String name = null;
    protected ArrayList<String> lore = new ArrayList<>();
    protected ItemStack item = new ItemStack(Material.AIR, 1);
}

ShopCommand.java

package me.myname.servername.commands;

import me.myname.servername.Utils.MakeItem;
import me.myname.servername.Utils.Weapon;
import me.myname.servername.items.weapons.BluntKnife;
import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.ItemStack;

public class ShopCommand implements CommandExecutor, MakeItem {

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args)
    {
        if(sender instanceof Player){
            Player player = (Player) sender;
            Inventory shopinv = Bukkit.createInventory(player, 9, ChatColor.AQUA   "Shop");
            BluntKnife item1 = new BluntKnife();


            ItemStack[] menu_items = {makeItemFromWeapon(item1)};


            shopinv.setContents(menu_items);
            player.openInventory(shopinv);
        }

        return true;
    }
}

CodePudding user response：

Of public interface MakeItem. An interface in Java is always public and static and All fields (variables) must be static constants and All methods are an abstract signature only , no body code You must "implement" the coded methods inside a class that uses the implement keyword and the interface name.

CodePudding user response：

In BluntKnife.java I did the constructor wrong.

So I changed it from public void BluntKnife() too public BluntKnife()