java - 我得到 java.lang.IndexOutOfBoundsExeption : Invalid index 9, 大小为 5

Question

当我从一个数组列表中删除一个项目并将其放置到另一个数组列表时，我不断收到此异常。有时索引是 13，大小是 5。其他时候是 0 和 0。它是随机发生的，并且在较慢的设备上更常见。

11-05 19:42:34.487: W/dalvikvm(2232): threadid=14: thread exiting with uncaught exception   (group=0x40c3ca68)
11-05 19:42:34.497: E/AndroidRuntime(2232): FATAL EXCEPTION: Thread-491
11-05 19:42:34.497: E/AndroidRuntime(2232): java.lang.IndexOutOfBoundsException: Invalid index size is 5
11-05 19:42:34.497: E/AndroidRuntime(2232):     at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at java.util.ArrayList.add(ArrayList.java:143)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at com.pigeoncraft.pigeoncraft.entity.Inventory.add(Inventory.java:25)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at com.pigeoncraft.pigeoncraft.screen.ContainerMenu.tick(ContainerMenu.java:62)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at com.pigeoncraft.pigeoncraft.Game.tick(Game.java:312)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at com.pigeoncraft.pigeoncraft.Game.iterate(Game.java:265)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at com.pigeoncraft.pigeoncraft.GameActivity$2.run(GameActivity.java:128)
11-05 19:42:34.497: E/AndroidRuntime(2232):     at java.lang.Thread.run(Thread.java:856)

这是库存代码。

    package com.mojang.ld22.entity;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import  com.pigeoncraft.pigeoncraft.item.Item;
import  com.pigeoncraft.pigeoncraft.ResourceItem;
import  com.pigeoncraft.pigeoncraft.Resource;

public class Inventory  implements Serializable {
private static final long serialVersionUID = -8246630353617240883L;

public List<Item> items = new ArrayList<Item>();

public void add(Item item) {
    add(items.size(), item);
}

public void add(int slot, Item item) {
    if (item instanceof ResourceItem) {
        ResourceItem toTake = (ResourceItem) item;
        ResourceItem has = findResource(toTake.resource);
        if (has == null) {
            items.add(slot, toTake); <--------------------
        } else {
            has.count += toTake.count;
        }
    } else {
        items.add(slot, item);
    }
}

private ResourceItem findResource(Resource resource) {
    for (int i = 0; i < items.size(); i++) {
        if (items.get(i) instanceof ResourceItem) {
            ResourceItem has = (ResourceItem) items.get(i);
            if (has.resource.name.equals(resource.name))
            {
                return has;
            }
        }
    }
    return null;
}

public boolean hasResources(Resource r, int count) {
    ResourceItem ri = findResource(r);
    if (ri == null) return false;
    return ri.count >= count;
}

public boolean removeResource(Resource r, int count) {
    ResourceItem ri = findResource(r);
    if (ri == null) return false;
    if (ri.count < count) return false;
    ri.count -= count;
    if (ri.count <= 0) items.remove(ri);
    return true;
}

public int count(Item item) {
    if (item instanceof ResourceItem) {
        ResourceItem ri = findResource(((ResourceItem)item).resource);
        if (ri!=null) return ri.count;
    } else {
        int count = 0;
        for (int i=0; i<items.size(); i++) {
            if (items.get(i).matches(item)) count++;
        }
        return count;
    }
    return 0;
}
}

Answer 1

在不确切知道代码在从 ArrayList 添加/删除对象时正在做什么的情况下，很明显这段代码根本不是线程安全的，因为您的方法/变量都没有同步。 ArrayList 本身就是这样，因为 Java 免费为您提供了它，但您的 add 方法甚至从不检查您是否尝试在可支持的索引处插入对象。在调用 add 之前，您至少应该检查是否 slot >= items.length() 这样您就可以将其附加到列表末尾，或者至少更优雅地退出