不应该使用ArrayList实现java NullPointerException？

2 月，2 周 Questions & Answers 824

今天我得到了一个NullPointerException，它实际上不可能发生

Exception in thread "Timer-9" java.lang.NullPointerException
    at packagename.censored.Bot.changeServergroups(Bot.java:1363)
    at packagename.censored.Bot.xpTask(Bot.java:1239)
    at packagename.censored.Bot.access$7(Bot.java:1187)
    at packagename.censored.Bot$9.run(Bot.java:729)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

这是守则的相关部分：

public void changeServergroups(int cldbid, ArrayList<Integer> addList, ArrayList<Integer> removeList) {
    // If there are groups to add AND delete, remove them from the lists
    if (addList != null && removeList != null) {
        ArrayList<Integer> temp = new ArrayList<Integer>(addList);
        for (int s : temp) { // THIS IS LINE 1363
            if (removeList.contains(s)) {
                addList.remove((Integer) s);
                removeList.remove((Integer) s);
            }
        }
    }
    // some more code, to do the actual group changes
}

如何在那里获取NullPointerException？在从中创建新的临时ArrayList之前，我检查以确保addList不为null。有人能告诉我这怎么可能以NullPointerException返回吗

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不应该使用ArrayList实现java NullPointerException？

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