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Hashtable doent allow null values ???

Naveen kumar.s
Greenhorn

Joined: Feb 10, 2010
Posts: 3
Many tutorials say that Hashtable doesnt allow null values,but i tried like
hashtable.put(" ","red");
and able to display it by using Object get(Object key);
and also i want to know whether Hashtable allow duplicates.

I think the only diff b/w HashMap and Hashtable is Hashtable is synchronized.

Am i right?
Pushkar Choudhary
Rancher

Joined: May 21, 2006
Posts: 425

Naveen kumar.s wrote:Many tutorials say that Hashtable doesnt allow null values,but i tried like
hashtable.put(" ","red");
and able to display it by using Object get(Object key);


" " is not a null value, it is a valid String with a single space. "" is also a valid empty String. Try putting null.
PrasannaKumar Sathiyanantham
Ranch Hand

Joined: Nov 12, 2009
Posts: 110
"" means an empty string or a string with length 0 . try using null you will get an error


To err is human,
To forgive is not company policy
Sagar Rohankar
Ranch Hand

Joined: Feb 19, 2008
Posts: 2902
    
    1

Welcome to JR !

The " " is empty string and NOT a null value. In Java, null is object, like


And hash is a key so it must be unique in order to retrieve the corresponding value.
Have look at the JavaDocs for the Hashtable for more info.

And yes, Hashtable is synchronized.


[LEARNING bLOG] | [Freelance Web Designer] | [and "Rohan" is part of my surname]
Sagar Rohankar
Ranch Hand

Joined: Feb 19, 2008
Posts: 2902
    
    1

and people are very quick here ;)
Naveen kumar.s
Greenhorn

Joined: Feb 10, 2010
Posts: 3
Hi,
thank you all for your replies,

but i still have doubts regarding null values in hash table.

i have entered null as key and when i use get("null"), the value that is paired to null key is being displayed.

for your reference am giving the code and output here.

Henry Wong
author
Sheriff

Joined: Sep 28, 2004
Posts: 18874
    
  40

Naveen kumar.s wrote:
i have entered null as key and when i use get("null"), the value that is paired to null key is being displayed.


null --> meaning null reference. Not a string with a value of "null".

Henry


Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor)
shan raj
Ranch Hand

Joined: Dec 16, 2008
Posts: 42
Hi,

Look at the previous response for the thread.

Here also you are using valid string "null" with length 4 as key used for storing the value and retrieving the value.


In your code try this

instead of


Thanks
shan

Naveen kumar.s
Greenhorn

Joined: Feb 10, 2010
Posts: 3
Thanks, yes that works well when i enter null instead of "null" as a key.

thank you all for your responses.
 
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