Hashtable class in collection framework

• A Hashtable is an array of list.Each list is known as a bucket.The position of bucket is identified by calling the hashcode() method. A Hashtable contains values based on the key. It implements the Map interface and extends Dictionary class.
• It contains only unique elements.
• It may have not have any null key or value.
• It is synchronized.

Like HashMap, Hashtable stores key/value pairs in a hash table. When using a Hashtable, you specify an object that is used as a key, and the value that you want 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.

Constructors:

The Hashtable defines four constructors. The first version is the default constructor:

Hashtable( )

The second version creates a hash table that has an initial size specified by size:

Hashtable(int size)

The third version creates a hash table that has an initial size specified by size and a fill ratio specified by fillRatio.

This ratio must be between 0.0 and 1.0, and it determines how full the hash table can be before it is resized upward.

Hashtable(int size, float fillRatio)

The fourth version creates a hash table that is initialized with the elements in m.

The capacity of the hash table is set to twice the number of elements in m. The default load factor of 0.75 is used.

Hashtable(Map m)

Methods:
Apart from the methods defined by Map interface, Hashtable defines following methods:

Example of Hashtable:

import java.util.*;
class Simple{
 public static void main(String args[]){
 
  Hashtable hm = new Hashtable();

  hm.put(100,"Dinesh");
  hm.put(102,"Sweety");
  hm.put(101,"Ankit");
  hm.put(103,"Nimmo");

  Set set = hm.entrySet();
  Iterator itr = set.iterator();

  while(itr.hasNext()){
   Map.Entry m=(Map.Entry)itr.next();
   System.out.println(m.getKey()+" "+m.getValue());
  }
 }
}