jrcheenu

 Profile Answers by jrcheenu Questions by jrcheenu

• Apr 23rd, 2008

 

There is null check in the put method implementation of hashtable, so it does not support null values and null keys

Subbarayudu Golla

 Profile Answers by Subbarayudu Golla 

• Jan 18th, 2011

 

HashTable:
1.) From the APIs, we can see, the objects which stored in the Hashtable should implement hashCode() and equals() methods.
2.) To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode method and the equals method.
HashMap:
 HashMap implementation does allow null keys. In the java.util.HashMap implementation, in case the key is null, it uses a surrogate object to act as the key. The surrogate key is a dummy non-null java object. However using a null key in HashMap overwrites the previous null-key : value mapping.

Vinay Kumar

• Nov 23rd, 2015

 

Hashtable is a legacy class. hash table doesnt allow duplicate object as a key and value beacause hashtable implements hashcode () method. Hash code method compute object hashcode number if object is a null as key and value then hashtable doesnt get any hash code of key or value then JVM throws NullPointerException. and if try to store null value in hashtable then Hashtable.get() method return null if key was absent would be ambiguous. in this case we cant store null object as key and value because hashtable implements hashcode() and equals() for calculate object.
This is a drawback of Hash table. Hashmap is newer class which is added JDK 1.2 version. HashMap developed for specially store one null key and many value and it is non-thread safe and non-synchronized what are drawback available in hashtable all feature provide in Hashmap.