Hashtable doent allow null values ???

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?

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.

"" means an empty string or a string with length 0 . try using null you will get an error

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.

and people are very quick here ;)

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.

import java.util.Hashtable;
import java.util.Enumeration; 
import java.util.Set;
import java.util.Iterator;

public class HashTableDemo {
	public static void main(String []args)	{
		Hashtable ht=new Hashtable(5);
		ht.put("Andhrapradesh","hyderabad");
		ht.put("Tamilnadu","chennai");
		ht.put("Karnataka","Banglore");
		ht.put("null","mumbai");
		ht.put("Karnataka","mysore");
		
		
		[b]System.out.println("null key value is :"+ht.get("null"));  [/b]
		
		Set s=ht.entrySet();
		System.out.println(s);

System.out.println();
		Set s1=ht.keySet();
		System.out.println(s1);

Iterator i=s1.iterator();
		System.out.println();
		while(i.hasNext())
		{
			System.out.println(i.next());
		}
		
		Enumeration e=ht.elements();
		ht.put("pondicherry","puducherry");
		System.out.println();
		while(e.hasMoreElements())
		{
			Object o=e.nextElement();
		System.out.println(o);
		}
		
	}

}

output:

[b]null key value is :mumbai [/b]   -----------> here it is
[Karnataka=mysore, [b]null=mumbai[/b], Tamilnadu=chennai, Andhrapradesh=hyderabad]

[Karnataka, [b]null[/b], Tamilnadu, Andhrapradesh]

Karnataka
[b]null[/b]
Tamilnadu
Andhrapradesh

mysore
[b]mumbai[/b]  ----> this is mapped to null key
chennai
puducherry
hyderabad

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

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

Thanks, yes that works well when i enter null instead of "null" as a key.

thank you all for your responses.