What are the differences between HashMap and HashTable in Java?

Question

Aryan Kumar · Answer

The HashMap and HashTable classes in Java are both implementations of the Map interface. They both use a hash table to store key-value pairs. However, there are some key differences between the two classes.
Synchronization: HashMap is not synchronized, while HashTable is synchronized. This means that HashMap can be accessed by multiple threads without synchronization, while HashTable must be synchronized to prevent race conditions.Null keys and values: HashMap allows one null key and multiple null values, while HashTable does not allow any null keys or values.Performance: HashMap is generally faster than HashTable, especially when it is not being accessed by multiple threads.
In general, HashMap is a good choice for applications that do not need to be thread-safe and that require high performance. HashTable is a good choice for applications that need to be thread-safe and that do not require high performance.
Here is a table that summarizes the key differences between HashMap and HashTable:
Feature
HashMap
HashTable
Synchronization
Not synchronized
Synchronized
Null keys and values
Allows one null key and multiple null values
Does not allow any null keys or values
Performance
Generally faster
Slower
Use cases
Applications that do not need to be thread-safe and that require high performance
Applications that need to be thread-safe and that do not require high performance

Mukul Goenka · Answer

HashMapand 
HashTable
HashMap is not synchronized thereby making it better for non-threaded applications.
HashTable is synchronized and hence it is suitable for threaded applications.
Allows only one null key but any number of null in the values.
This does not allow null in both keys or values.
Supports order of insertion by making use of its subclass LinkedHashMap.
Order of insertion is not guaranteed in HashTable.

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What are the differences between HashMap and HashTable in Java?

Mukul Goenka

2 Answers

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Feature	HashMap	HashTable
Synchronization	Not synchronized	Synchronized
Null keys and values	Allows one null key and multiple null values	Does not allow any null keys or values
Performance	Generally faster	Slower
Use cases	Applications that do not need to be thread-safe and that require high performance	Applications that need to be thread-safe and that do not require high performance

HashMap	HashTable
HashMap is not synchronized thereby making it better for non-threaded applications.	HashTable is synchronized and hence it is suitable for threaded applications.
Allows only one null key but any number of null in the values.	This does not allow null in both keys or values.
Supports order of insertion by making use of its subclass LinkedHashMap.	Order of insertion is not guaranteed in HashTable.