Answer / sarithareddy

Hashmap work as like as Hashtable but hashtable is
synchronised hash map was not sychronized
hashtable does not allow null values
hashmap allows null values

Answer / chandan phukan

Two main differences between Hastable and HashMap are

1. Hashtable is synchronised but HashMap is not.
2. Hashtable does not allow "null" key but HashMap allows
"null" Key.

However one point to remember is that only one "null" key is
allowed in HashMap but multiple "null" values are allowed in
HashMap.

Answer / arun rajesh

The HashMap class is roughly equivalent to Hashtable,
except that it is unsynchronized and permits nulls.
(HashMap allows null values as key and value whereas
Hashtable doesnt allow).

HashMap does not guarantee that the order of the map will
remain constant over time. HashMap is unsynchronized and
Hashtable is synchronized.

Answer / knowledge_finder

1. HashMap allows null values for key and value whereas
Hashtable doesnt allow.
2. HashMap does not guarantee that the order of the map will
remain constant over time. 3. HashMap is non synchronized
where as Hashtable is synchronized.
4. HashTable is an Old java class but Hashmap is a new java
class in java 2.
5. In HashTable you can change the iteration but in the case
of HashMap you can change the iteration but you will get a
java.util.ConcurrentModificationException.

Answer / suresh

HashMap hm=new HashMap();
hm.put("1","11");
hm.put("2","22");
hm.put("3","33");
hm.put("4","242");
hm.put(null,null);
hm.put(null,null);
HashMap also allow more null values

Answer / regalla naresh reddy

Hash Table is a legacy Class Whereas HashMap belongs to the
collections package.

HashMap allows null key and values..but it allows only one
null key and multiple null values...Whereas the HashTable
wont allow the null key and values..

Answer / prabhat ranjan

You all said that HashMap allows 1 null key and mulitple
null values but why ? What was the basic idea behind it
making such feature by JAVA bulider ?

Answer / venkatesh marni

in the HashMap & Hashtable wen ever key values are Same then
it maps only to the value which is mapped at last.
REFER to the ANS.9 above we can access only one value.

but Hashtable is Synchronized one and it wont stores any
null values.

Answer / green

HashTable is a Legacy Class,where as HashMap is not.
HashTable is Syncronized,where as HashMap is not.
HashTable does not allow any null keys nad values, HashMap
allows one null key and 'n' number null values.
comparatively HashMap is faster then HashTable

Answer / ashad

Hash Table is a legacy Class Whereas HashMap belongs to the
collections package.

HashMap allows null key and values..but it allows only one
null key and multiple null values...Whereas the HashTable
wont allow the null key and values..


HashMap allows only one null key, basic idea behind it is
that key can have unique value only if one null is assigned
to a key next null will be duplicate.

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