java - 如何使用空键处理迭代中的空指针

Question

在最近的一次采访中，我面临的问题是

How can you handle null pointer when iterator encounters a null key while iteration over a hashmap. assume my developer has inserted a null key by mistake

我的答案是:只是我们需要检查null!=entry.getKey()。他不满意，之前就说你要怎么处理。

我该如何回答这个问题。当我回来的时候。

我试过了

public class Main {
    public static void main(String[] args) {
        Map<String,String> map = new HashMap<String,String>();
        map.put(null, "null");
        map.put("null",null);
        map.put("test", "test");

        Iterator<Entry<String, String>> it = map.entrySet().iterator();
        while(it.hasNext()){
            System.out.println(it.next().getKey());
        }
    }
} 

输出:

null
test
null

没有异常(exception)。他到底想问什么。或者是我遗漏了一些概念？请指导我

Answer 1

map.remove(null)

来自 JavaDocs:

Returns the value to which this map previously associated the key, or null if the map contained no mapping for the key.

If this map permits null values, then a return value of null does not necessarily indicate that the map contained no mapping for the key; it's also possible that the map explicitly mapped the key to null.

The map will not contain a mapping for the specified key once the call returns.

在迭代之前调用它，它将删除显式的空键