Hashmap vs Hashtable

HashMap and Hashtable store key and value pairs in a hash table. When using a Hashtable or HashMap, we specify an object that is used as a key and the value that you want to be linked to that key. The key is then hashed, and the resulting hash code is used as the index at which the value is stored within the table.

• HashMap is non-synchronized. It is not thread-safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.
• HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value.
• HashMap is generally preferred over HashTable if thread synchronization is not needed.

Program:

// Java program to demonstrate

// HashMap and HashTable

import java.util.*;

import java.lang.*;

import java.io.*;

// Name of the class has to be "Main"

// only if the class is public

class Ideone

{

public static void main(String args[])

{

//----------hashtable -------------------------

Hashtable<Integer,String> ht=new Hashtable<Integer,String>();

ht.put(101," ajay");

ht.put(101,"Vijay");

ht.put(102,"Ravi");

ht.put(103,"Rahul");

System.out.println("-------------Hash table--------------");

for (Map.Entry m:ht.entrySet()) {

System.out.println(m.getKey()+" "+m.getValue());

}

//----------------hashmap--------------------------------

HashMap<Integer,String> hm=new HashMap<Integer,String>();

hm.put(100,"Amit");

hm.put(104,"Amit");

hm.put(101,"Vijay");

hm.put(102,"Rahul");

System.out.println("-----------Hash map-----------");

for (Map.Entry m:hm.entrySet()) {

System.out.println(m.getKey()+" "+m.getValue());

}

}

}

Output:

-------------Hash table--------------

103 Rahul

102 Ravi

101 Vijay

-----------Hash map-----------

100 Amit

101 Vijay

102 Rahul

104 Amit