Which is faster HashMap or Hashtable?

The HashMap is faster than the Hashtable. The HashMap is faster since it is non-synchronized whereas Hashtable is synchronised and hence slower. The HashMap is preferred over Hashtable.

When should we use HashMap and Hashtable?

Whenever we use and want synchronized data structure we use the HashMap whereas for the unsynchronised and faster data, we use Hashtable. Whenever we want to allow null key, we use the HashMap.

As per the inheritance, what is the difference between HashMap and Hashtable?

As per the inheritance, in the HashMap abstract class is inherited whereas in Hashtable dictionary class is inherited. The inheritance in both the data structures are different.

Can HashMap have duplicate keys?

No, HashMap do not carry duplicate keys. The old key is replaced as and when a duplicate key is inserted in the Map. The duplicate key is not hold in the arrangement of the data by HashMap.

Difference Between HashMap and Hashtable

By Mohit Uniyal|Updated : June 14th, 2022

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Difference between HashMap and Hashtable: Data structures are used to store and organize the data. Both HashMap and Hashtable are a type of data structures. The map interface is hashed and Mapped with both data structures. The major difference between the HashMap and Hashtable is that Hashtable can not allow the null values and null key whereas a HashMap can allow it.

The comparison of Hashtable and HashMap is widely asked in various interview processes. Here, 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.

Table of Content

1. Difference Between HashMap and Hashtable
2. What is HashMap in Java?
3. What is Hashtable in Java?

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Difference Between HashMap and Hashtable

There exist differences between HashMap and Hashtable such as Hashtable is synchronized and HashMap is not synchronized. Other differences between the two data structures are shown in the table provided below:

Key Differences between HashMap and Hashtable

HashMap	Hashtable
It is non-synchronized.	It is synchronized.
Thread-safe.	Thread-unsafe.
Faster than Hashtable.	Slower than HashMap.
It can allow one null key.	Can not allow null key.
Traversed by Iterator.	Traversed by Enumerator and Iterator.
Carries fail-fast iterator.	Does not carry a fail-fast iterator.
AbstractMap class is inherited.	Dictionary class is inherited.
Can carry various null values.	Can not carry null values.

What is HashMap in Java?

The HashMap is used for the implementation of the Map interface in Java. Since it is a type of data structure, it is used to save the data. The data is stored in the form of keys and values. The key and value can be accessed with the index of another type. The HashMap is unsynchronized.

The single null key and multiple null values can be stored with the HashMap. The syntax of the HashMap is shown below:

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

Where, K is the type of the keys on the map, and V is the type of values mapped on the map.

What is Hashtable in Java?

Hashtable is also a type of data structure and hence is used to store or arrange data. This data structure also stores data in the form of key and value pairs. The hashtable comprises the following parts:

Hash Function
Array

In Hashtable, non-null objects can be stored as a value and key pairs but null values are not stored in this, unlike HashMap. This is a synchronized way of storing data. The syntax of the Hashtable is shown below:

public class Hashtable<K,V> extends Dictionary<K,V> implements Map<K,V>, Cloneable, Serializable

Where, K is the type of the keys on the map, and V is the type of values mapped on the map.

Check out some important topics related to the difference between HashMap and Hashtable in the table provided below:

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FAQs on Difference Between HashMap and Hashtable

What is the major difference between the HashMap and Hashtable?
The major difference between the HashMap and hashtable is that null values can not be stored in Hashtable whereas in HashMap we can store the null values and a single null key.
Which is faster HashMap or Hashtable?
The HashMap is faster than the Hashtable. The HashMap is faster since it is non-synchronized whereas Hashtable is synchronised and hence slower. The HashMap is preferred over Hashtable.
When should we use HashMap and Hashtable?
Whenever we use and want synchronized data structure we use the HashMap whereas for the unsynchronised and faster data, we use Hashtable. Whenever we want to allow null key, we use the HashMap.
As per the inheritance, what is the difference between HashMap and Hashtable?
As per the inheritance, in the HashMap abstract class is inherited whereas in Hashtable dictionary class is inherited. The inheritance in both the data structures are different.
Can HashMap have duplicate keys?
No, HashMap do not carry duplicate keys. The old key is replaced as and when a duplicate key is inserted in the Map. The duplicate key is not hold in the arrangement of the data by HashMap.