paste

package me.gianlucapmc.guns;

import java.util.ArrayList;

import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.entity.Fireball;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDamageByEntityEvent;
import org.bukkit.event.player.PlayerInteractEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.plugin.java.JavaPlugin;

public class Guns extends JavaPlugin implements Listener {

    /* This part is tricky: I've made multiple ArrayLists to allow each gun to have different damage */
    private ArrayList<Fireball> normalGun = new ArrayList<Fireball>();
    private ArrayList<Fireball> stoneGun = new ArrayList<Fireball>();
    private ArrayList<Fireball> ironGun = new ArrayList<Fireball>();
    private ArrayList<Fireball> goldGun = new ArrayList<Fireball>();
    private ArrayList<Fireball> diamondGun = new ArrayList<Fireball>();

    public void onEnable() {
        /* Has to register the events from the class (this) and the plugin (which is also this) */
        Bukkit.getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler
    public void onPlayerInteract(PlayerInteractEvent e) {
        if(e.getPlayer().getItemInHand() != null) {
            /* In your old code, you forgot to check if they contain the specific item (blaze powder, clay ball etc.) */
            if(e.getPlayer().getInventory().contains(Material.FLINT)) {
                if (e.getPlayer().getItemInHand() != null && e.getPlayer().getItemInHand().getType().equals(Material.WOOD_HOE)) {
                    Fireball f = e.getPlayer().launchProjectile(Fireball.class);
                    f.setYield(0);
                    normalGun.add(f);
                    removeItem(e.getPlayer(), Material.FLINT);
                }
            } else if(e.getPlayer().getInventory().contains(Material.COAL)) {
                if (e.getPlayer().getItemInHand() != null && e.getPlayer().getItemInHand().getType().equals(Material.STONE_HOE)) {
                    Fireball f = e.getPlayer().launchProjectile(Fireball.class);
                    f.setYield(0);
                    stoneGun.add(f);
                    removeItem(e.getPlayer(), Material.COAL);
                }
            } else if(e.getPlayer().getInventory().contains(Material.BLAZE_POWDER)) {
                if (e.getPlayer().getItemInHand() != null && e.getPlayer().getItemInHand().getType().equals(Material.IRON_HOE)) {
                    Fireball f = e.getPlayer().launchProjectile(Fireball.class);
                    f.setYield(0);
                    ironGun.add(f);
                    removeItem(e.getPlayer(), Material.BLAZE_POWDER);
                }
            } else if(e.getPlayer().getInventory().contains(Material.CLAY_BALL)) {
                if (e.getPlayer().getItemInHand() != null && e.getPlayer().getItemInHand().getType().equals(Material.GOLD_HOE)) {
                    Fireball f = e.getPlayer().launchProjectile(Fireball.class);
                    f.setYield(0);
                    goldGun.add(f);
                    removeItem(e.getPlayer(), Material.CLAY_BALL);
                }
            } else if(e.getPlayer().getInventory().contains(Material.REDSTONE)) {
                if (e.getPlayer().getItemInHand() != null && e.getPlayer().getItemInHand().getType().equals(Material.DIAMOND_HOE)) {
                    Fireball f = e.getPlayer().launchProjectile(Fireball.class);
                    f.setYield(0);
                    diamondGun.add(f);
                    removeItem(e.getPlayer(), Material.REDSTONE);
                }
            }
        }

    }

    @EventHandler
    public void onEntityDamage(EntityDamageByEntityEvent e) {
        if (e.getDamager() instanceof Fireball) {
            Fireball f = (Fireball) e.getDamager();
            if (normalGun.contains(f)) {
                e.setDamage(10);
                return;
            } else if(stoneGun.contains(f)) {
                e.setDamage(20);
                return;
            } else if(ironGun.contains(f)) {
                e.setDamage(35);
                return;
            } else if(goldGun.contains(f)) {
                e.setDamage(25);
                return;
            } else if(diamondGun.contains(f)) {
                e.setDamage(50);
                return;
            }
        }
        return;
    }

    /* I'm putting this here for simplicity */
    private void removeItem(Player p, Material material) {
        int slot = p.getInventory().first(material);
        ItemStack is = p.getInventory().getItem(slot);
        if (is.getAmount() <= 1) {
            p.getInventory().setItem(slot, null);
            return;
        } else {
            is.setAmount(is.getAmount() - 1);
            return;
        }
    }
}