java - 读取枚举时出现空指针

Question

看来我遇到了一些麻烦。我正在尝试读取枚举中的随机值，尽管在尝试执行此操作时遇到了空指针。我不完全确定这里出了什么问题，但希望有人能教我我做错了什么!

所以，这是我得到的错误:

java.lang.NullPointerException at com.foxtrot.game.player.dialogues.impl.npcs.Child.run(Child.java:89) at com.foxtrot.game.player.DialogueManager.continueDialogue(DialogueManager.java:31) at com.foxtrot.net.decoders.WorldPacketsDecoder.processPackets(WorldPacketsDecoder.java:1127) at com.foxtrot.net.decoders.WorldPacketsDecoder.decode(WorldPacketsDecoder.java:282) at com.foxtrot.net.ServerChannelHandler.messageReceived(ServerChannelHandler.java:128) at org.jboss.netty.channel.SimpleChannelHandler.handleUpstream(SimpleChannelHandler.java:88) at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564) at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:559) at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268) at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255) at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:88) at org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:108) at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318) at org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:89) at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178) at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108) at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)

这是我收到错误的语句:

        if (player.getMonsterTask() == null) {
            player.getMonsterTask().applyTask();
            int amount = monsterHandler.getAmount();
            int id = player.getMonsterTask().getId();
            String name = NPCDefinitions.getNPCDefinitions(id).getName();
            send("Go, warrior! Go and kill ", "x"+amount+" of "+name+"!");
            return;
        }

player.getMonsterTask().applyTask(); 是第 89 行。

public enum tasks {

    ROCK_CRAB(1265, 5, 50, 1, 7500),
    MAGIC_AXE(127, 5, 15, 1, 3000),
    CHAOS_DRUID(181, 5, 30, 1, 4000),
    MAN(2, 2, 10, 1, 1000),
    ROCK_GOLEM(3027, 1, 3, 1, 10000),
    GIANT_BAT(78, 5, 20, 1, 5000),
    OGRE(3419, 5, 60, 20, 12000),
    POISON_SPIDER(134, 10, 50, 25, 15000),
    CHAOS_DWARF(119, 5, 60, 30, 15000),
    CYCLOPS(6081, 15, 40, 35, 18000),
    ICE_WOLF(6052, 15, 40, 35, 19000),
    GIANT_SPIDER(2035, 15, 70, 40, 20000),
    HILL_GIANT(117, 15, 55, 45, 50000),
    MOSS_GIANT(1681, 20, 50, 47, 25000),
    GIANT_ROCK_CRAB(2885, 10, 90, 75, 75000);

    private int id, minAmount, maxAmount, levelReq, reward;
    private Player player;
    private MonsterHandler monsterHandler;
    public boolean completed = false;

    private static final List<tasks> VALUES = Collections.unmodifiableList(Arrays.asList(values()));
    private static final int SIZE = VALUES.size();
    private static final Random RANDOM = new Random();

    tasks(int id, int minAmount, int maxAmount, int level, int reward) {
        this.id = id;
        this.minAmount = minAmount;
        this.maxAmount = maxAmount;
        this.levelReq = level;
        this.reward = reward;
    }

    public int getReward() {
        return reward;
    }

    public int getLevelReq() {
        return levelReq;
    }

    public int getId() {
        return id;
    }

    public int getMinAmount() {
        return minAmount;
    }

    public int getMaxAmount() {
        return maxAmount;
    }

    public void getMonsterTask() {
        player.setMonsterTask(VALUES.get(RANDOM.nextInt(SIZE)));
    }

    public boolean isComplete() {
        return completed;
    }

    public void setComplete(boolean b) {
        this.completed = b;
    }

    public void setReward(int r) {
        this.reward = r;
    }

    public void resetMonster(Player player) {
        player.getMonsterTask().setComplete(false);
        player.getMonsterTask().setNpcId(-1);
        player.getMonsterTask().setReward(-1);
        monsterHandler.setAmount(-1);
        player.setMonsterTask(null);
    }

    public void setNpcId(int id) {
        this.id = id;
    }           

}

这是我的 MonsterTasks 类，applyTask 方法是从其中提取的。如果您需要更多信息，请告诉我!

谢谢。

Answer 1

if (player.getMonsterTask() == null) 这意味着player.getMonsterTask()实际上返回了null。
在下一行 player.getMonsterTask().applyTask(); 中，您实际上正在执行 null.applyTask()。因此异常(exception)。