HashMap v/s Hashtable

In this article, we will discuss difference between HashMap and Hashtable classes in detail i.e.; HashMap v/s Hashtable

Key points about Java Hashtable:

Hashtable is legacy class and based on hashcode of keys where keys are unique and it is exactly same as HashMap with few differences with respect to following points

  • Synchronized methods
  • Performance
  • Null key insertion
  • Null value insertion

Lets us move on and discuss key differences between these 2 Map implemented classes

HashMap v/s Hashtable:

HashMap Hashtable
HashMap is introduced in collection framework in Java 1.2 version Hashtable is a legacy class and introduced in Java 1.0 version
HashMap is NOT synchronized Hashtable is synchronized
All methods of HashMap is NOT synchronized i.e.; it is not thread-safe All methods of HashMap is synchronized i.e.; thread-safe
Multiple threads are allowed to access Only one thread is allowed access; other threads has to wait to get access, after obtaining lock/monitor
Performance-wise, this is relatively high comparing with Hashtable, as there is no wait time Performance-wise, this is relatively slow due synchronized methods as there is only one thread allowed to access, at any given point of time
NULL insertion allowed for both keys and values NULL insertion is not allowed for both keys and values
Maximum of one NULL key and there is no upper limit for values Simply, not allowed for both keys & values

Note: both uses hash table data structure to store key-value pairs

When to use HashMap ?

  • HashMap stores key-value pairs which uses hashing technique to store key-value pairs where methods are NOT synchronized
  • So, search operation is faster with multiple threads access
  • So, if business requirement is to store key-value pairs for faster search operation or more number of search operation on the basis of keys; without concerning concurrent access of map
  • Then, HashMap is the very apt choice

When to use Java Hashtable ?

  • This is exactly same as that of HashMap, but every methods is synchronized
  • Performance-wise is relatively slower than comparing HashMap
  • So, if business requirement is to store key-value pairs for faster search operation with synchronized access
  • Then, Java Hashtable is preferred choice over HashMap

 

1. Program on HashMap :

DemoHashMap.java

package in.bench.resources.collection;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class DemoHashMap {

	public static void main(String[] args) {
		// 1. Creating HashMap object
		Map<Integer, String> hashMap = 
				new HashMap<Integer, String>();

		// 1.1 add few entries
		hashMap.put(40, "RajKumarHirani");
		hashMap.put(50, "SanjayLeelaBanshali");
		hashMap.put(20, "Shankar");
		hashMap.put(10, "ManiRatnam");
		hashMap.put(30, "RajaMouli");
		hashMap.put(null, null);

		// 1.2 get entrySet()
		Set<Map.Entry<Integer, String>> entries = hashMap.entrySet();	

		System.out.println("Displaying HashMap entries"
				+ " in Random-order : \n");

		// 1.3 Iterate using enhanced for-Each loop
		for(Map.Entry<Integer, String> entry : entries) {
			System.out.println("Rank : " + entry.getKey() 
					+ "\t Director : " + entry.getValue());
		}
	}
}

Output:

Displaying HashMap entries in Random-order : 

Rank : null	 Director : null
Rank : 50	 Director : SanjayLeelaBanshali
Rank : 20	 Director : Shankar
Rank : 40	 Director : RajKumarHirani
Rank : 10	 Director : ManiRatnam
Rank : 30	 Director : RajaMouli

 

2. Program on Hashtable :

DemoHashtable.java

package in.bench.resources.collection;

import java.util.Hashtable;
import java.util.Map;
import java.util.Set;

public class DemoHashtable {

	public static void main(String[] args) {

		// 1. Creating Hashtable object
		Map<Integer, String> hashtable = 
				new Hashtable<Integer, String>();

		// 1.1 add few entries
		hashtable.put(40, "RajKumarHirani");
		hashtable.put(20, "Shankar");
		hashtable.put(10, "ManiRatnam");
		hashtable.put(50, "SanjayLeelaBanshali");
		hashtable.put(30, "RajaMouli");

		// 1.2 get entrySet()
		Set<Map.Entry<Integer, String>> entries = hashtable.entrySet();	

		System.out.println("Displaying Hashtable entries"
				+ " in Random-order : \n");

		// 1.3 Iterate using enhanced for-Each loop
		for(Map.Entry<Integer, String> entry : entries) {
			System.out.println("Rank : " + entry.getKey() 
					+ "\t Director : " + entry.getValue());
		}
	}
}

Output:

Displaying Hashtable entries in Random-order : 

Rank : 10	 Director : ManiRatnam
Rank : 20	 Director : Shankar
Rank : 30	 Director : RajaMouli
Rank : 40	 Director : RajKumarHirani
Rank : 50	 Director : SanjayLeelaBanshali

 

References:                                                                                                            

 

Happy Coding !!
Happy Learning !!

Properties class
Hashtable class