为什么variable.add（索引，元素）创建一个空错误？

Question

我花了很多时间来解决这个问题，你可以从所有的打印稿中看到。所以我需要问一下。为什么blocks.add可以工作，但labels.add却出现错误null？

我的故障排除println返回“添加标签[1]：强度”，所以我知道值在里面。

void load() {       
    String path = "menus.inventorys.stats";
    System.out.println("setting variables");
    // now load stat details from config
    System.out.println("default name");
    String defaultName = statConfig.getDefaults().getString(path + ".name");
    System.out.println("done");
    System.out.println("defaultslots");
    int defaultSlots = statConfig.getDefaults().getInt(path + ".slots");
    System.out.println("done");
    System.out.println("mame");
    name = statConfig.getString(path + ".name", defaultName);
    System.out.println("done");
    System.out.println("slots");
    slots = statConfig.getInt(path + ".slots", defaultSlots);
    System.out.println("done");

    InventoryController inventory = new InventoryController();
    ArrayList<Material> blocks = new ArrayList<>();
    ArrayList<String> labels = new ArrayList<>();
    ArrayList<String> slots = new ArrayList<>();

    if (statConfig.isSet(path + "slot")) {
        System.out.println("path to slots exists");
    }

    System.out.println("beginning loop");
    for (String slot : statConfig.getConfigurationSection(path + ".slot").getKeys(false)) {
        System.out.println("iterating material");
        Material block = (Material) statConfig.get(path + ".slot." + slot + ".block");
        System.out.println("material found");
        System.out.println("iterating label");
        String label = statConfig.getString(path + ".slot." + slot + ".label");
        System.out.println("label found");
        System.out.println("adding block");
        blocks.add(block);
        System.out.println("done");
        int blockSize = blocks.size();
        System.out.println("adding labels[" + blockSize + "]: " + label);
        labels.add(blockSize, label);
        System.out.println("done");
        System.out.println("adding slot");
        slots.add(blocks.size(), label);  // remember this is seperate from the arraylist for the block ItemStacks we will need to call this seperately
        System.out.println("done");
    }

[16:17:08][服务器线程/信息]:done[16:17:08][服务器线程/信息]:添加html" target="_blank">标签[1]:Strength[16:17:08][服务器线程/信息]:done[16:17:08][服务器线程/信息]:添加slot[16:17:08][服务器线程/错误]:null org . buk kit . command . command异常:在org . buk kit . command . plugin command的插件rift v0.0.1中执行命令' rift '时出现未处理的异常。craft server . dispatch command(craft server . Java:646)~[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at net . minecraft . server . v1 _ 8 _ R2。net.minecraft.server.v1_8_R2的player connection . handle command(player connection . Java:1133)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]。net.minecraft.server.v1_8_R2的player connection . a(player connection . Java:968)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]。packet playin chat . a(packet playin chat . Java:45)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at net . minecraft . server . v1 _ 8 _ R2。packet playin chat . a(packet playin chat . Java:1)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at net . minecraft . server . v1 _ 8 _ R2。PlayerConnectionUtils $ 1 . run(Source file:13)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at Java . util . concurrent . executors $ runnable adapter . call(未知来源)[？:1 . 8 . 0 _ 51]at Java . util . concurrent . future task . run(未知来源)[？:1 . 8 . 0 _ 51]at net . minecraft . server . v1 _ 8 _ R2。net.minecraft.server.v1_8_R2的SystemUtils.a(源文件:60)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]。minecraft server . A(minecraft server . Java:710)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at net . minecraft . server . v1 _ 8 _ R2。位于net.minecraft.server.v1_8_R2的DedicatedServer . A(DedicatedServer . Java:368)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]。minecraft server . z(minecraft server . Java:651)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at net . minecraft . server . v1 _ 8 _ R2。minecraft server . run(minecraft server . Java:554)[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]at Java . lang . thread . run(未知来源)[？:1.8.0_51]原因:Java . lang . indexoutofboundsexception:Index:1，Size:0 at Java . util . ArrayList . rangecheckforadd(未知来源)~[？:1.8.0_51]在java.util.ArrayList.add(未知来源)~[？:1 . 8 . 0 _ 51]at com . au . msh craft . rift . stat model . load(stat controller . Java:201)~[？:?]at com . au . msh craft . rift . stat controller . open(stat controller . Java:52)~[？:?]at com . au . msh craft . rift . rift . stat view(rift . Java:100)~[？:?]at com . au . msh craft . rift . rift . on command(rift . Java:81)~[？:?]at org . buk kit . command . plugincommand . execute(plugincommand . Java:44)~[Spigot-1.8 _ server . jar:git-Spigot-DBE 012 b-61ef 214]...还有15个

Answer 1

您收到错误是因为您没有初始化标签ArrayList中的元素。如果您从index0开始添加，它将起作用，但由于index1尚未为您初始化，它将导致indexoutofb的异常。