界限必须是积极的

Question

这是我不断收到的错误，我理解，但无法修复，因为我不知道问题出在哪里。

[14:25:50 ERROR]: Could not pass event BlockBreakEvent to SurgeGlowstone v1.0
org.bukkit.event.EventException
        at org.bukkit.plugin.java.JavaPluginLoader.execute(JavaPluginLoader.java:297) ~[custom.jar:git-PaperSpigot-a925999]
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[custom.jar:git-PaperSpigot-a925999]
        at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:513) [custom.jar:git-PaperSpigot-a925999]
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:498) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.PlayerInteractManager.breakBlock(PlayerInteractManager.java:264) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.PlayerInteractManager.dig(PlayerInteractManager.java:118) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:569) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.PacketPlayInBlockDig.a(PacketPlayInBlockDig.java:41) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.PacketPlayInBlockDig.handle(PacketPlayInBlockDig.java:65) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:189) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:103) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:801) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:286) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:651) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:557) [custom.jar:git-PaperSpigot-a925999]
        at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [custom.jar:git-PaperSpigot-a925999]
Caused by: java.lang.IllegalArgumentException: bound must be positive
        at java.util.Random.nextInt(Random.java:388) ~[?:1.8.0_131]
        at com.surgehcf.listeners.PlayerListener.onBreak(PlayerListener.java:49) ~[?:?]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_131]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_131]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_131]

这是我的代码：

public static int randInt(int min, int max) {

    // NOTE: This will (intentionally) not run as written so that folks
    // copy-pasting have to think about how to initialize their
    // Random instance.  Initialization of the Random instance is outside
    // the main scope of the question, but some decent options are to have
    // a field that is initialized once and then re-used as needed or to
    // use ThreadLocalRandom (if using at least Java 1.7).
    Random rand = new Random();

    // nextInt is normally exclusive of the top value,
    // so add 1 to make it inclusive
    int randomNum = rand.nextInt((max - min) + 1) + min;

    return randomNum;
}
@EventHandler
public void onBreak(BlockBreakEvent e) {
    Player p = e.getPlayer();
    Block b = e.getBlock();
    JsonBox bx = GlowstoneMountain.getInstance().getRegionAqui(b.getLocation());
    if (bx != null && b.getType() == Material.GLOWSTONE && b.getWorld().getName().equalsIgnoreCase("world_nether")) {
        b.getWorld().dropItemNaturally(b.getLocation(), new ItemStack(Material.GLOWSTONE_DUST,randInt(4,2)));
    }
}

我总是做一个 4 到 2 之间的随机整数。但是，它仍然说否定我想要的：一个 2 到 4 之间的整数，以获得随机输出。

Answer 1

在 onBreak() 方法中，在 if 语句中，更改为：

new ItemStack(Material.GLOWSTONE_DUST,randInt(4,2)));

对此：

new ItemStack(Material.GLOWSTONE_DUST,randInt(2,4)));

现在您正在尝试获取一个最大为 2 最小为 4 的随机整数。这是不可能的。改成最大4个，最小2个。

randInt() 函数的参数顺序为 (min, max)。目前您将其视为 (max, min).

Answer 2

要了解错误（以及如何修复），请查看 Java docs on Random's nextInt():

Parameters:

bound - the upper bound (exclusive). Must be positive.

Throws:

IllegalArgumentException - if bound is not positive

但是，randInt(4,2)，正如您所说的方法，是完全错误的方法。它使用 4 作为 min，2 作为 max，因此你最终得到一个负边界（-1），导致异常。

因此，我建议对您的方法进行以下更改：

public static int randInt(int a, int b) {
    int min = Math.min(a, b);
    int max = Math.max(a, b);
    return rand.nextInt((max - min) + 1) + min;
}

解释：

现在，您相信函数的用户会遵守参数的顺序（min, max - 而不是 max, min）。虽然您可以做到这一点，但您刚刚体验到这会给您带来麻烦的速度有多快，即使用户是您。

因此，像上面那样添加安全措施将导致更健壮的代码。在这里，我们只是检查两个值中的哪一个是 smaller and which is the bigger 那个，然后相应地使用它们。

当然，您也可以保持方法不变，只需将调用更改为 randInt(2,4)。

注：

用户仍然有可能让您的方法中断（如上所示抛出异常），但我将把它作为练习留给您，让您弄清楚如何 - 以及如何防止它。 :-)