java - Bukkit 插件编码不起作用？

Question

首先，我是 Java 新手。这是我的第一个 bukkit 插件，唯一的错误是这个( Click Here )。该插件的目标是，当您右键单击“基岩 splinter 机”时，它会破坏基岩。

package me.jrneulight.bedrockbreaker;


import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockBreakEvent;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.PlayerInventory;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.plugin.java.JavaPlugin;

public final class Main extends JavaPlugin implements Listener {
    public static void main(String[] args) {

    }
    @Override
    public void onEnable() {
        getLogger().info("Breakrock Breaker Enabled!");
        getServer().getPluginManager().registerEvents(this, this);
    }
    @Override
    public void onDisable() {
        getLogger().info("Bedrock Breaker Disabled!");
    }
    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args){
        if(cmd.getName().equalsIgnoreCase("bedrockbreaker")){ 
            Player player = (Player) sender;
            PlayerInventory inventory = player.getInventory();

            ItemStack bedrockbreaker = new ItemStack(Material.DIAMOND_HOE,1);

            ItemMeta im = bedrockbreaker.getItemMeta();

            im.setDisplayName(ChatColor.DARK_AQUA + "Bedrock Breaker");
            bedrockbreaker.setItemMeta(im);
            inventory.addItem(bedrockbreaker);
            return true;
        } 

        return false; 
    }
    @EventHandler(priority=EventPriority.HIGH)
    public void onPlayerUse (org.bukkit.event.player.PlayerInteractEvent evnt) {
        org.bukkit.block.Block block = evnt.getClickedBlock();
        org.bukkit.inventory.ItemStack item = evnt.getItem();
        Player player = evnt.getPlayer();
        org.bukkit.World world = block.getWorld();
        ItemMeta itemmeta = item.getItemMeta();
            if (block.getType() == Material.BEDROCK && item.getType() == Material.DIAMOND_HOE && itemmeta.getDisplayName() == ChatColor.DARK_AQUA + "Bedrock Breaker") {

                BlockBreakEvent breakEvent = new BlockBreakEvent(block, player);
                getServer().getPluginManager().callEvent(breakEvent);
                ItemStack drop = new ItemStack(block.getType());
                drop.setAmount(1);
                drop.setType(Material.BEDROCK);
                block.setType(Material.AIR);

                world.dropItemNaturally(block.getLocation(), drop);
                player.sendMessage("Bedrock Broken!");
            }
    }
}

Answer 1

如您的错误所示，此处:

Caused by: java.lang.NullPointerException
    at me.jrneulight.bedrockbreaker.Main.onPlayerUse(Main.java:54)

您将在 Main 文件的第 54 行获得一个 NullPointer。意味着 54 行上的某些内容的值为 null。首先，让我先让 onPlayerUse 开头的代码变得更好。您不必使用 org.bukkit.block.Block block，只需使用 Block block = evnt.getClickedBlock(); 同样适用于 org.bukkit.inventory.ItemStack，只需要使用ItemStack即可。

该错误是由于您的方法在没有单击任何 block 时尝试单击该 block ，或者在未使用任何 block 时尝试获取所使用的项目而引起的。这是您应该使用的代码:

@EventHandler(priority=EventPriority.HIGH)
public void onPlayerUse (PlayerInteractEvent evnt) {
    if(evnt.getAction().equals(Action.LEFT_CLICK_BLOCK){//make sure that they are infact hitting a block
        if(evt.getItem() == new ItemStack(Material.DIAMOND_HOE)){ //make sure they are using a diamond hoe
            Block block = evnt.getClickedBlock();
            //ItemStack item = evnt.getItem();
            //we don't need the above line any more
            Player player = evnt.getPlayer();

            World world = block.getWorld();
            ItemMeta itemmeta = item.getItemMeta();
         }
    }
}

因此，对于整个 onPlayerUse 方法，您应该使用以下代码:

    @EventHandler(priority=EventPriority.HIGH)
    public void onPlayerUse (PlayerInteractEvent evnt) {
        if(evnt.getAction().equals(Action.LEFT_CLICK_BLOCK)){//make sure that they are infact hitting a block
            if(evnt.getItem() == new ItemStack(Material.DIAMOND_HOE)){ //make sure they are using a diamond hoe
               if(evnt.getItem().getItemMeta().getDisplayName().equals(ChatColor.DARK_AQUA + "Bedrock Breaker")){ //make sure the name of the diamond hoe is "Bedrock Breaker" in DARK_AQUA

                Block block = evnt.getClickedBlock();
                World world = block.getWorld();
                Player player = evnt.getPlayer();
                if(block.getType() == Material.BEDROCK){ //make sure the block clicked is bedrock

                    BlockBreakEvent breakEvent = new BlockBreakEvent(block, player);
                    Bukkit.getServer().getPluginManager().callEvent(breakEvent);
                    ItemStack drop = new ItemStack(block.getType());
                    drop.setAmount(1);
                    drop.setType(Material.BEDROCK);
                    block.setType(Material.AIR);

                    world.dropItemNaturally(block.getLocation(), drop);
                    player.sendMessage("Bedrock Broken!");
                }
            }
        }
    }
    }

您需要使用 .equals(String) 而不是 == String 检查名称。此外，您应该首先检查大多数要求以减少延迟。

您收到该错误的原因是因为您不确定他们是否击中了方 block ，因此，在您的代码中，当玩家执行任何操作时(踩在压力板上，右键单击一个项目) ，击中空气)，它称你为代码。这就是为什么您需要确保他们使用 Action.LEFT_CLICK_BLOCK 左键单击一个 block ，然后获取他们正在点击的 block 。在你尝试获取他们正在击中的方 block 之前，即使他们按下按钮或踩在压力板上，也会返回一个 NullPointerException，因为没有任何方 block 被击中。

作为一般经验法则，在您从事件中获取某些内容之前，首先检查您要获取的内容是否存在。