The Hashtable Class

In this section, you will learn about Hashtable and its implementation with the help of example.


How to read properties file in Java? Generate random numbers in Java Cloneable Interface in Java What is the flaw with the Stack class? List In Java Java Stack Example HashSet In Java Enumeration in java How to generate random number in java Iterator in java Queue in java Transient Java Keyword clone method in Java Java Queue example Logger in Java Java current date - How to get current date in Java Collection : LinkedList Example Collection : ArrayList Example Random alpha numeric string of fixed size Java List Iterator Example The Hashtable Class The BitSet class Java Vector Java Enumeration Data Structures in Java Java Transient Variable Java Date Format Example Java Properties File Example Map.Entry Java Interface Java Property File java preferences,Change the value of Preferences by user Retrieving a Preference Node Java hasNext Write Keys and Values to the Properties file in Java Get All Keys and Values of the Properties files in Java Properties file in Java Properties file in Java Determining If a Preference Node Contains a Specific Value Change the value of Preferences by user Clone method example in Java Implementing a Simple Event Notifier Determining When a Preference Node Is Added or Removed Listening for Changes to Preference Values in a Preference Node Importing Preferences Finding a Preference in a Preference Tree Retrieving the Parent and Child Nodes of a Preference Node Determining If a Preference Node Exists Removing a Preference Node Creating a Preference Node Getting the Maximum Size of a Preference Key and Value

The Hashtable Class

In this section, you will learn about Hashtable and its implementation with the help of example.

Hashtable is integrated with the collection framework and also implements the Map interface. Similar to HashMap it also stores key/value pair in Hashtable. But the difference is Hashtable is synchronized.

Hashtable supports 4 types of constructor :

(1) The first constructor is the default constructor. It's syntax is:


(2) The second constructor provide freedom to user to define initial size of the Hashtable. Syntax is below :

Hashtable(int size)

(3) In third constructor, user can define its initial size and and a fill ratio specified by load factor.

Hashtable(int size, float load factor)

The load factor is a measure of how full the hash table is allowed to get before its capacity is automatically increased. It's value must lie in between 0.0 and 1.0.

(4) In fourth Hashtable, user can pass a Map as argument. It provide the same mapping as in the provided Map but the capacity of the hash table is twice the number of elements in the passed Map. Syntax is provided below :

Hashtable(Map m)

It also has its own method. In spite of that , it also supports Map interface methods. Click here for complete list of Hashtable's method.


import java.util.*;

public class HashTableExample {
public static void main(String args[]) {
// Create a hash map
Hashtable ht = new Hashtable();
Enumeration htenum;
String str;
double bal;

ht.put("Neha", new Double(3434.34));
ht.put("Ankit", new Double(123.22));
ht.put("Rohit", new Double(1378.00));
ht.put("Vinay", new Double(99.22));
ht.put("Vijay", new Double(-19.08));

// Show all balances in hash table.
htenum = ht.keys();
while (htenum.hasMoreElements()) {
str = (String) htenum.nextElement();
System.out.println(str + ": " + ht.get(str));
// Deposit 1,000 into Neha's account
bal = ((Double) ht.get("Neha")).doubleValue();
ht.put("Neha", new Double(bal + 1000));
System.out.println("Neha's new balance: " + ht.get("Neha"));


Ankit: 123.22
Neha: 3434.34
Rohit: 1378.0
Vijay: -19.08
Vinay: 99.22

Neha's new balance: 4434.34             

Download Source Code


Share on Google+Share on Google+

The Hashtable Class

Posted on: August 3, 2011 If you enjoyed this post then why not add us on Google+? Add us to your Circles



Discuss: The Hashtable Class  

Post your Comment

Your Name (*) :
Your Email :
Subject (*):
Your Comment (*):
  Reload Image