HashMap Vs HashTable

HashMap

HashMap is the basic implementation of the map interface in Java. HashMap stores the data in key and value pairs. Keys are used to access the value of the element.

It is declared as < k ,v >.

HashMap is similar to HashTable, but HashMap is unsynchronized. It follows hashing technique to store the key and value pairs. To use HashMap, we must import the java. Util package.

Syntax

HashMap <k ,v> hashmapname = new HashMap < >( );

Here k and v represent the datatype of key and value pairs.

Example for HashMap Program

HashMap.java

// importing the required packages
// util package is required to implement hashmap 
import java. util. HashMap ;
import java . io . * ;
class HashMap {
  public static void main( String[] args) {
    // create a hashmap
    HashMap < String , Integer> h1  = new HashMap < > ();
    // adding  elements to hashmap
    h1 . put ( " Hi " ,  2);
    h1 . put ( " Hello " ,  3);
    h1 . put ( " Everyone " ,  8);
    System . out. println ( " HashMap is : " + h1);
  } // Main
}//  HashMap

Output

Operations on HashMap

• Add elements
• Remove elements
• Access elements
• Alter elements

Adding Elements to HashMap

To add elements to HashMap, we use the put ( ) method.

AddElements.java

 import java. util. HashMap;
import java . io . * ;
class AddElements {
  public static void main( String[] args) {
    // Object creation for hashmap with name h
    HashMap < String, Integer> h  = new HashMap < > ();
    // add elements to hashmap
    h . put (" One " , 1);
    h . put (" Two " , 2);
    h . put (" Three " , 3);
    System . out. println("HashMap is : " + h);
  } // Main
} // AddElements

Remove Elements in HashMap

To remove elements in HashMap, we use the remove ( ) method.

RemoveElements.java

import java. util. HashMap;
import java . io . * ;
class RemoveElements {
  public static void main( String[] args) {
    // create a hashmap
    HashMap < String, Integer> h2  = new HashMap < > ();
    // add elements to hashmap
    h2 . put ( " One " , 1);
    h2 . put ( " Two " , 2);
    h2 . put ( " Three " , 3);
    h2 . put ( " Four " , 4);
    System . out. println ( " Before removing elements the HashMap is : " + h2 );
    // removing the element with the key "Two."
    h2 . remove ( "  Two " ) ;
    System . out. println ( " After removing element the HashMap is : "  + h2 ) ;
  } // main
}  // RemoveElements

Output

Access Elements in HashMap

To access the elements in HashMap, we use the get method

AccessElement.java

import java. util. HashMap;
import java . io . * ;
class AccessElement {
  public static void main( String[] args) {
    // create a hashmap
    HashMap < Integer,String>  h3 = new HashMap <> ();
    // add elements to hashmap
    h3 . put(1," One ");
    h3 . put(2," Two ");
    h3 . put(3," Three ");
    h3 . put(4," Four ");
    // Printing the HashMap elements
    System . out. println (" Elements of  the HashMap is : " + h3);
    // Accessing the elements of the HashMap
     String value = h3 . get (3);
     // Printing the value of element at index 3
    System . out . println (" Value at index : " + value);
  } // main
}

Output

Change Elements in HashMap

HashMap is mutable. We can change the data of the HashMap by using replace ( ) method.

AlterElements.java

import java. util. HashMap;
import java . io . * ;
class Alterelements {
  public static void main( String[] args) {
    // create a hashmap
    HashMap < Integer,String> h4  = new HashMap <> ();
    // add elements to hashmap
    h4 . put(1," One ");
    h4 . put(2," Two ");
    h4 . put(3," Three ");
    h4 . put(4," Four ");
    // Printing the HashMap elements
    System . out. println (" Elements of  the HashMap before changing the data is: " + h4);
    // Changing the value of element at index 4 from four to changed
    h4. replace (4," changed ");
    // Printing the Elements of HashMap after altering it
    System . out. println (" Elements of  the HashMap after changing the data is : " + h4); 
  } // Main
} //AlterElements

Output

HashTable

HashTable is the basic implementation of the map interface in Java. HashTable stores the data in key and value pairs. Keys are used to access the value of the element.

It is declared as < k ,v >. It is a synchronised data structure.

Syntax

HashTable <k ,v> hashtablename = new HashTable < >( );

Example for HashTable Program

HashTableExample.java

import java.util.*;  
class HashTableExample{ 
 public static void main(String args[]){  
     // Hashtable declaration
  Hashtable <  String, Integer  > h1 = new Hashtable <  String ,Integer>();  
  // Adding data to Hashtable
  h1 . put ( "Om" , 201  ) ;  
  h1 . put (  "Sai" , 202  ) ;  
  h1 . put ( "Ram", 203  ) ;  
  // Accessing the data of Hashtable
  for( Map . Entry r : h1 . entrySet ( ) ){  
   System . out . println ( r . getKey ( ) + "   " + r . getValue ( ) ) ;  
  }  // for
 }  // main
}  // HashTableExample

Output

Operations on HashMap

• Add elements
• Remove elements
• Access elements

Add Elements to HashTable in Java

To add elements to HashTable, we use the put ( ) method.

AddElements.java

import java .io .*;
import java . util . *;  
class AddElements { 
 public static void main ( String args [ ] ) {  
     // Hashtable declaration
  Hashtable <  String, Integer  > h1 = new Hashtable <  String ,Integer>();  
  // Adding data to Hashtable
  h1 . put ( "Om" , 201  ) ;  
  h1 . put (  "Sai" , 202  ) ;  
  h1 . put ( "Ram", 203  ) ;  
  // Printing the data of Hashtable
   
   System . out . println (h1) ;  
 
 }  // main
}  // AddElements

Output

Remove Elements to HashTable in Java

To add elements to HashTable, we use the remove ( ) method.

RemoveElements.java

import java .io .*;
import java . util . *;  
class RemoveElements { 
 public static void main ( String args [ ] ) {  
     // Hashtable declaration
  Hashtable <  String, Integer  > h1 = new Hashtable <  String ,Integer>();  
  // Adding data to Hashtable
  h1 . put ( "Om" , 201  ) ;  
  h1 . put (  "Sai" , 202  ) ;  
  h1 . put ( "Ram", 203  ) ; 
  // Before removing the element from Hashtable
   System . out . println ("Hashtable  before removing is"+h1) ; 
  // Printing the data of Hashtable
   h1 .remove("Om");
   System . out . println ("After removing element from Hashtable"+h1) ;  
 }  // main
}  // RemoveElements

Output

Access Elements of HashTable in Java

AccessElements.java

import java.util.*;  
class AccessElements{ 
 public static void main(String args[]){  
     // Hashtable declaration
  Hashtable <  String, Integer  > h1 = new Hashtable <  String ,Integer>();  
  // Adding data to Hashtable
  h1 . put ( "Om" , 201  ) ;  
  h1 . put (  "Sai" , 202  ) ;  
  h1 . put ( "Ram", 203  ) ;  
  // Accessing the data of Hashtable
  for( Map . Entry r : h1 . entrySet ( ) ){  
   System . out . println ( r . getKey ( ) + "   " + r . getValue ( ) ) ;  
  }  // for
 }  // main
}  // AccessElemets

Output

Differences between HashMap and HashTable