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LinkedHashMap vs HashMap

The LinkedHashMap is quite similar to HashMap, with an additional feature of maintaining the order of the inserted element. HashMap provides an easy way to insert, delete, and search the elements, but it does not provide any way to maintain and track the order of the inserted elements. Here, LinkedHashmap came into the picture, which overcomes this issue.

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. Whereas the LinkedHashMap is an alternative to HashMap that has the support of maintaining the order of the elements.

The LinkedHashMap inherits the HashMap class and implements the Map interface of the Java Collection frameworks.

HashMap

HashMap in Java is a powerful data structure that allows us to store the key-pair values. It allows us to store the null value objects. We can not insert the duplicate key; if we try, it will replace that element corresponding to the respected key. We can easily perform operations such as updation, deletion, etc., on the objects. The HashMap class can be found in java.util package.

Declaration:

The HashMap class is declared as follows:

Some key points about HashMap are as following:

  • It contains key-pair values.
  • It can not have duplicate keys.
  • It may have one null key and multiple null values.
  • It is non-synchronized.
  • It does not provide a way to maintain the order of elements.
  • The default capacity of the Java HashMap class is 16 with a load factor of 0.75.

Example:

Consider the below example to implement the HashMap and store the key-pair values:

Output:

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

LinkedHashMap

The LinkedHashMap class is an alternative to the HashMap class. It is quite similar to the HashMap class. As it inherits the HashMap class, so it holds all the properties and methods of the HashMap class. Additionally. It provides an easy way to maintain the order of the elements. The LinkedHashMap inherits the HashMap class and implements the Map interface.

Declaration:

The LinkedHashMap class is declared as follows:

Some key points about the LinkedHashMap are as following:

  • It stores the values in the key-pair combination.
  • It can not have duplicate elements.
  • It may have one null key and multiple null values.
  • It is non synchronized.
  • It provides an easy way to maintain the insertion order

Example:

Consider the below example to implement the LinkedHashMap and store vlaues in it:

Output:

100 John
101 Dev
102 Arya
103 Zoya

Difference Between LinkedHashMap and HashMap

The LinkedHashMap is an alternative to HashMap with some additional features. The following are some major differences between LinkedHashMap and HashMap:

  • The Major Difference between the HashMap and LinkedHashMap is the ordering of the elements. The LinkedHashMap provides a way to order and trace the elements. Comparatively, the HashMap does not support the ordering of the elements. In LinkedHashMap, if we iterate an element, we will get a key in the order in which the elements were inserted.
  • The HashMap and LinkedHashMap both allow only one null key and multiple values.
  • The HashMap extends AbstractMap class and implements Map interface, whereas the LinkedHashMap extends HashMap class and implements Map interface.
  • Both LinkedHashMap and HashMap are non-synchronized, but they can be synchronized using the Collections.synchronizedMap() method.
  • The HashMap uses a bucket to store the elements, which is an index of the array like bucket0 means index[0], bucket1 means index[1], and so on, of the array. Whereas the LinkedHashMap uses the same internal implementation as HashMap but, Apart from that, it also uses a doubly-linked through all of its entries. This linked list is useful for ordering the elements.
  • The HashMap requires low memory than LinkedHashMap; because the LinkedHashMap uses the same implementation process as HashMap; additionally, it uses a doubly LinkedList to maintain the order of the elements.
  • Both the LinkedHashMap and HashMap provides similar performance.

Comparison Table of LinkedHashMap and HashMap

Consider the below comparison table of HashMap and LinkedHashMap:

Property HashMap LinkedHashMap
Order of Iteration No guarantee order Insertion order
Implements (Interface) Map Map
Null key/values Only one null key & multiple values Only one null key & multiple values
Implementation Buckets Double-linked buckets
Synchronized Non-synchronized non-synchronized
Performance Fast Almost Similar to HashMap
Extends AbstractMap class HashMap class
Memory Low Memory More memory as compared to HashMap.
Thread-safety Non-thread-safe Non-thread-safe

Summary:

As we have discussed, both HashMap and LinkedHashMap data structures; both are powerful data structure. The HashMap is useful for the general-purpose hashing based collection, and the LinkedHashmap is useful for managing the chaotic ordering of the elements.






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