Answer / 20/04/2008

hashmap class is not syncronized but hasTable is syncronized
. both stores key and value. hashtable is part of legasy
class we can use enumerator interface of this hashtable class.

Answer / rameshreddy.k

---HashTable is synchronised BUT hashmap is not synchronised
---HashTable not allow null keys and null values BUT
HashMap allow only one null key and multiple null values
---HashTable not allow Duplicate keys and Douplicate values
are allowed.

Answer / leosun

Hashtable will not allow null key nor values,where as
Hashmap allows null key and values

Answer / venki

1. Hashtable is synchronized which means Hashtable is thread
safe and that can be shared with multiple threads (Suitable
for multi threaded applications), HashMap not synchronized
(Suitable for single threaded applications).
2. Iterator in the Hashtable is fail-fast iterator and throw
ConcurrentModificationException if any other thread modifies
the map by adding or removing elements from the Map, while
Emnumeration in HashMap not.
3. Hashtable is slower than HashMap because of synchronization.
4. HashTable does not allow null for both keys and values,
you will get NullPointerException if you add null. whereas
HashMap allows one null key and any number of null values.
5. Hashtable and HashMap allows duplicate values.
6. Hashtable store objects in insertion order but HashMap
doesn’t store objects in insertion order, to store objects
in insertion order use LinkedHashMap.

Answer / sivadasan

Hashmap is not Synchronized where as Hashtable is
Synchronized.

Hashmap allows null values as keys.
Hashtable doesn't allows null values as keys.

How do you check if a number is a perfect square?

0 Answers  

What classes of exceptions may be thrown by a throw statement?

0 Answers  

I want to persist data of objects for later use. What is the best approach to do so?

0 Answers  

can we write a program with out a class in core java?

11 Answers   Wipro,

my method "abc" return array of interface "xyz" and "pqr" is abstract class implements abc and class "jkl" extends pqr My problem 1) when i call abc it retrun array xyz how can i do this hint xyz refer_xyz = new jkl(); but i can't create array. 2)I want to access method of jkl using reference of xyz??

1 Answers  

when we have to use final class in java?

2 Answers  

what is abstract method with example?

6 Answers   Infosys, Virtusa,

What is purpose of keyword void?

0 Answers  

take any 4 input numbers. like 2345.. wanted out put is All 16 combinations of the number 2345.. for example- taking input as 4565 output- 5654 4556 4655..

2 Answers   Emphasis,

In C we use only compiler. Why java uses both compiler and interpreter? What is its significance?

5 Answers  

Explain about narrowing conversion in java?

0 Answers  

What is a package in java? List down various advantages of packages.

0 Answers