java - 遍历HashMap时，我得到NullPointerException

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这是我的代码：

HashMap<String, HashSet<String>> map;
....// I didn't write those code that initial the map.
System.out.println(map.entrySet().size()); // run util here is ok, I get the size of the map.
for(Map.Entry<String, HashSet<String>> entry : map.entrySet()) {// here throw the exception
    Sytem.out.println("abc");// didn't executed, throw exception before
}

我得到一个例外：

线程“主”中的异常java.lang.NullPointerException
    在key.test.EnwikiOutlink.main（EnwikiOutlink.java:68）

该地图对象有10,000多个地图对象，我在服务器计算机上运行它并且无法调试。
但是，当我减小此地图的大小（小于10,000）时，程序运行正常。
问题的原因是什么，解决方案是什么？谢谢！

最佳答案

map在哪里初始化？如果您实际上没有为其分配任何内容，则它当然是null。

（尚不清楚它是类成员还是局部变量。）