HashMap 中 NULL 键的哈希码

问题描述

我只是在阅读 Java 中 HashMap 和 HashTable 类之间的区别.在那里我发现了一个区别，前者允许空键，而后者不允许相同的权限.就 HashMap 的工作而言，我知道，它在 key 上调用 hashcode 方法来查找要放置该键值对的存储桶.我的问题来了:如何计算空值的哈希码或空键的哈希码是否有任何默认值(如果有，请指定值)?

I was just reading about the difference between HashMap and HashTable class in java. There I found a difference that former allow null key and later doesn't privileges for the same. As far as the working of HashMap is concern I know that, it calls hashcode method on key for finding the bucket in which that key value pair is to be placed. Here comes my question: How hashcode for a null value is computed or Is there any default value for hashcode of null key (if so please specify the value)?

推荐答案

from HashMap:

from HashMap:

public V put(K key, V value) {
   if (key == null)
      return putForNullKey(value);
   ...

如果你进一步看，你会发现 null 总是进入 bin 0

and if you look further you will see that null always goes to bin 0

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