Difference between Map and HashMap

The Map is an interface in Java used to map the key-pair values. It is used to insert, update, remove the elements. Whereas the HashMap is a class of Java collection framework.

The Map interface can only be used with an implementing class. It allows to store the values in key-pair combination; it does not allow duplicate keys; however, we can store the duplicate values. Its implementing classes are as follows:

HashMap is a powerful data structure in Java used to store the key-pair values. It maps a value by its associated key. It allows us to store the null values and null keys. It is a non-synchronized class of Java collection.

Implementation of the Map Interface

The Map interface can be implemented by using the implementing class. Consider the below example:

import java.util.*;
public class MapExample {
		public static void main(String args[]) 
		{ 
			Map<String, Integer> m 
				= new HashMap<String, Integer>(); //implementation of the Map Interface

			m.put("Abhi", new Integer(001)); //Adding elements
			m.put("Nick", new Integer(002)); 
			m.put("Ketty", new Integer(003)); 
			m.put("Paul", new Integer(004)); 
			for (Map.Entry<String, Integer> me : m.entrySet())// Traversing of the elements through the Map 
			{ 
				System.out.print(me.getKey() + ":"); 
				System.out.println(me.getValue()); 
			} 
		} 
	} 

Output:

Nick:2
Abhi:1
Paul:4
Ketty:3

Implementation of the HashMap Class

HashMap class can be declared as follows:

public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable  

Consider the below example to implement the HashMap:

//Java program to store the key-pair values using HashMap
import java.util.*;
public class HashMapDemo {
	 public static void main(String args[]){  
	  //HashMap implementation
		 HashMap<Integer,String> m=new HashMap<Integer,String>();//Creating HashMap    
	   m.put(1,"Chris");  //Adding elements in Map  
	   m.put(2,"Morris");    
	   m.put(3,"Sam");   
	   m.put(4,"Cruise");    
	   System.out.println("Iterating Hashmap...");  
	   for(Map.Entry me : m.entrySet()){    
	    System.out.println(me.getKey()+" "+me.getValue());    
	   }  
	}  
	}  

Output:

Iterating Hashmap...
1 Chris
2 Morris
3 Sam
4 Cruise

Key Differences between Map and HashMap

Some key differences between the Map and HashMap are as follows:

The Map is an interface, and HashMap is a class of the Java collection framework.
The Map interface can be implemented by using its implementing classes. In comparison, the HashMap class implements the Map interface.
The Map contains unique key-pair values. But, the HashMap can hold duplicate values.
The Map does not allow null values. But the HashMap can have one null key and multiple values.
The Map has two implementations, which are HashMap and TreeMap. Whereas HashMap implements Map interface and extends AbstractMap class.
There is no difference between the Map and HashMap objects.

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