HashTable overview

It’s basically designed to store key value pairs

HashTable class implements the Map interface and it inherits Dictionary class

Main features of HashTable

It stores data in the form of key-value pair

HashTable is the Synchronized data structure

Keys in the HashTable must be unique

It does not allow Null key and Null value

It does not maintain the order of insertion

Value can be retrieved by passing key

If passed key is not exist in the HashTable then value returned will be Null

HashTable can be created using constructor as below

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

Most Important Methods in HashTable

put(Object key, Object value)

This method stores the specified value and associates it with the specified key in this hash table.

get(Object key)

This method will return the value associated with a specified key in hash table.

We can add key value pair as below

  1. ht.put(1,”one”);

We can retrieve value for the specific key as

  1. ht.get(1);


  1. import java.util.*;
  2. public class HashTableExample {
  3. public static void main(String args[]) {
  4.  Hashtable<Integer,String> hashTable=new Hashtable<Integer,String>();
  5.       hashTable.put(1, "One");
  6.       hashTable.put(2, "Two");
  7.       hashTable.put(3, "Three");
  8.       hashTable.put(4, "Four");
  9.       hashTable.put(5, "Five");
  10. System.out.println(hashTable);
  11. System.out.println("Value for the key 1 is "+ hashTable.get(1));
  12. System.out.println("Value for the key 10 is "+ hashTable.get(10));
  13. }
  14. }
import java.util.*;
public class HashTableExample {
public static void main(String args[]) {
 Hashtable<Integer,String> hashTable=new Hashtable<Integer,String>(); 
      hashTable.put(1, "One");
      hashTable.put(2, "Two");
      hashTable.put(3, "Three");
      hashTable.put(4, "Four");
      hashTable.put(5, "Five");
System.out.println("Value for the key 1 is "+ hashTable.get(1));
System.out.println("Value for the key 10 is "+ hashTable.get(10));
Note : We can see that corresponding value for existing key is retrieved and value for non-existing key is returned as Null

When to use HashTable?

Whenever we want to store data in key-value pair format
Whenever we want synchronized key value pair data structure

When not to use HashTable ?

Whenever we have collection of elements without any link in that data like key value pair
Whenever we do not need synchronized key-value pair data structure

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Founder of javainsimpleway.com
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