In what situation do we need null key ?

hashmap supports null key (and null value). but I can't come up with a situation that we need null key (and null value).
Any idea ?

I too am guessing here. I've always been thinking, they couldn't find the good argument why nobody would ever want to have a null key. By permitting it, they make sure that this does not prevent anyone from using the class.
Also, you may consider what happens if someone absolutely wants it the other way than it's designed:
1. If they had forbidden the null key, the user could build a subclass that allows the null key.
2. With the design at hand, a user could build a subclass that disallows the null key.
Which situation leaves the user with the easier task? I believe #2 does. Which I think is a fine thing about the design they've chosen.
I know I didn't answer your question. I can't.
Edited by: OleVV on Oct 10, 2007 3:31 PM

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