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Hashtable and Hashmap Doubt

Abhi vijay
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Joined: Sep 16, 2008
Posts: 509
I read in K&B Book that,

Hashmap allows one null key and multiple null values in a collection. wheras Hashtable dosent let you add anything that's null.


Why is this distinction as both are unsorted, unordered?
Punit Singh
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Joined: Oct 16, 2008
Posts: 952
Hashtable is thread-safe Abhi, and it was there in java since 1.0, you can see its naming convention "t" in Hashtable is written in small. It was designed such that it will not allow any null key or null value.


But HashMap is added in java 1.2 version, so designer thought null should be allowed. Reason I do not know, any sheriff or knowledgeable guy could say the reason.



SCJP 6
Duran Harris
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Joined: Nov 09, 2008
Posts: 598

Punit,

You just inserted MULTIPLE null keys into the hashMap...
why was there no exception?


===>SCJP 1.5(72%)<===
==>SCWCD1.5(76%)<===
Punit Singh
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Joined: Oct 16, 2008
Posts: 952
HashMap does not store duplicate values. So although I have inserted multiple key, it will store only one null key and set the latest value to it.

Run this code, and tell me what you learned ?
Vijitha Kumara
Bartender

Joined: Mar 24, 2008
Posts: 3860

Duran Harris wrote:

You just inserted MULTIPLE null keys into the hashMap...
why was there no exception?


If the map previously contained the same key the old value is replaced.


SCJP 5 | SCWCD 5
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Duran Harris
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Joined: Nov 09, 2008
Posts: 598

Oh ok...Got it
 
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subject: Hashtable and Hashmap Doubt