This means nothing special. They just decided to have separate code for the put-logic if the key is null
, and they separated that code from the non-null code into method putForNullKey
.
When you look at put
you will find the if-clause that checks for null-keys and - if so - delegates to putForNullKey
:
public V put(K key, V value) {
if (key == null)
return putForNullKey(value);
// ... here comes the put code for non-null-keys
}