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Understand the Difference Between Hashmap Vs Hashtable

HashMap and Hashtable are data structures in Java that associate keys with values. The two data structures are so similar to one another that, in some applications, leveraging either implementation would not make a difference.

Even though HashMap and Hashtable are relatively similar, it is still vital to know when to use them because using them wrongly could have unfavorable effects. In this article, get an in-depth Hashmap Vs Hashtable comparison, and learn what makes them unique from one another. In this guide we will first see the difference between HashMap and Hashtable based on a few important factors and then we will see what is Hashtable and HashMap. 

Hashmap vs Hashtable: Differences Between Hashmap and Hashtable

Here, we will see the difference between HashMap and Hashtable based on a few important factors:

Basis Hashmap Hashtable
Definition Hashmap, a type of nap implementation, leverages hashtable for storage. It is a Legacy Map deployment that, too, leverages Hashtable for storage.
Thread Safety No Yes
Null Keys Permitted Not Permitted
Use Cases Map Implementation for General Purpose Legacy Map Implementation and Thread safe
Performance Faster Than Hashtable Slower Than Hashmap
Null Values Permitted Not Permitted
Iterator Fail Fast Not Fail Fast
Inheritance Extends AbstractMap Extends Dictionary

Hashmap Vs Hashtable: Coding Example

Here is a proper illustration of Hashmap Vs Hashtable at work for your better understanding:

import java.util.*;
import java.lang.*;
import java.io.*;
public class JavaTester{
   public static void main(String args[]){
      Hashtable ht=new Hashtable();
      ht.put(1,”Rohan”);
      ht.put(1,”Rishi”);
      ht.put(2,”Gaurav”);
      ht.put(3,”Rudra”);
      System.out.println(“————-Hash table————–“);
      Set keySet = ht.keySet();
      for (Integer key:keySet) {
         System.out.println(key + ” “+ht.get(key));
      }
      HashMap hm=new HashMap();
      hm.put(0,”Rohan”);
      hm.put(4,”Rohan”); // you can have duplicate values in a hashmap
      hm.put(1,”Gaurav”);
      hm.put(2,”Rudra”);
      System.out.println(“———–Hash map———–“);
      Set keySet1 = ht.keySet();
      for (Integer key:keySet) {
         System.out.println(key + ” “+hm.get(key));
      }
   }
}

Output: 

Hash table: 

3 Rudra
2 Gaurav
1 Rishi

Hash map:

0 Rohan
1 Gaurav
2 Rudra
4 Rohan

hashmap vs hashtable

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Hashmap vs Hashtable: Usage and Recommendations

Let’s deep dive into the difference between HashMap and Hashtable based on a usage and recommendations. 

Java supports both HashMap and Hashtable as key-value data structures. Hash tables are used in both cases, although there are some significant distinctions between them. Because HashMap isn’t synchronized, it’s not thread-safe. This means that multiple threads cannot safely access a HashMap simultaneously. However, since synchronization checks are unnecessary, HashMap is quicker than Hashtable. 

Hashtable is thread-safe because it is synchronized. This indicates that concurrent access by several threads to a hashtable is not problematic. However, since synchronization checks are required, Hashtable is slower than HashMap. 

Recommendations:

For Hashmap:

  • If you don’t need thread safety, use hash maps. 
  • HashMaps are used for this purpose the most frequently. 
  • HashMaps are suitable for situations where performance is crucial because they are faster than Hashtables. 

For Hashtable:

  • If you need thread safety, use a hashtable. 
  • Hashtables are useful for applications where many threads must access the same data structure since they are thread-safe. 
  • Hashtables should only be used when thread safety is necessary because they are slower than HashMaps. 

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Now we have seen the major difference between Hashmap and Hashtable. Now let’s move on to understand what is Hashmap and Hashtable individually.

What is a Hashmap?

HashMap is one of the Java collection classes. When it comes to Hashmap Vs Hashtable, the former implements the Map interface using a table-based extension of the AbstractMap class. HashMap is an unsynchronized data structure that supports many null values but only one null key object. 

Learn More: Top Programming Languages to Learn

Hashing Function

In this Hashmap Vs Hashtable section, check out the key Hashmap functions. 

  • Accepts null keys; null values store map entries in an inner node (K, V). 
  • Entries are kept in several linked lists, like buckets and bins. 
  • Uses keys for put and get operations and applies the hashCode() and equals() methods, which is a good implementation of these techniques. 
  • It is not multi-threaded environment-compatible and is not thread-safe. 

Pros and Cons of Hashmap

Pros of Hashmap Cons of Hashmap
Hashmap can look up items in an instance, thanks to their ability to map a key to a bucket in the hash table in seconds.  Collisions happen when two keys hash to the same bucket. It can considerably slow down the lookups and inserts. 
Due to the fact that just the keys and values—not the elements' order—need to be stored, hashmaps can be extremely memory-efficient. Since hashmaps don't maintain the order of the items, they are inappropriate for applications where it matters.
Hashmaps may be thread-safe, allowing many threads to access it concurrently without running into problems. Implementing hashmaps can be difficult, particularly if you need to construct your own Hash algorithm. 

What is a Hashtable?

The HashTable class is widely used to create a hash table that links and associates keys with values. Non-null objects are acceptable here as both a key and a value. Remember that the objects you use as keys must support both the equals and hashCode methods to successfully store and retrieve objects from a hashtable. 

hashmap vs hashtable

Hashing Function

In this Hashmap Vs Hashtable section, explore the various Hashtable functions: 

  • Contains original components built within the collections framework 
  • It prohibits using null values or keys. 
  • It is well-synchronized. 
  • The Hashtable class’s default loadFactor value is 0.75, and its default capacity is 11. 

Pros and Cons of Hashtable

Pros of Hashtable Cons of Hashtable
It ensures perpetual time lookups. Values can typically be looked up using hash tables in a fixed amount of time. Collisions, which happen when two separate keys hash to the same value, might affect hash tables.
Since only the key and value of each item need to be stored, hash tables can be incredibly space-efficient. Since hash tables aren't properly ordered, it can be challenging to iterate through the elements in a particular sequence.
A hash function and a collision avoidance method are the only tools to create hash tables. Nil

FAQ's

In the Java util package, Collection and Map are both interfaces. The collection stores objects, while Map stores items in a (key, value) based manner. Objects are stored as arrays using collection classes. The Map classes store data using the (KEY, VALUE) pair format.
When it comes to Hashmap Vs Hashtable, their key distinction is that a Hashmap is capable of storing both a single null key and null values, whereas a hashtable can’t even contain null values.
When comparing Hashmap Vs Hashtable, the former (Hashmap) is faster than the latter (Hashtable). Since the HashMap is not synchronized, it is faster than the Hashtable, which is synced and, therefore, slower. Over the Hashtable, the HashMap is preferable.
Since Java 1.2, HashMap has been a component of the Java collection. The Java.util package contains this class. It offers the fundamental Java Map interface implementation.
Hash tables serve the purpose of swiftly storing and retrieving information or data. With the use of hash keys, hashtables store the data in buckets.

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