What is the difference between hashmap and linkedhashmap

A LinkedHashMap is useful whenever you need the ordering of keys to match the ordering of insertion. This might be useful in a caching situation, when you want to delete the oldest item. Generally, unless there is a reason not to, you would use HashMap. That is, if you need to get the keys back in insertion order, then use LinkedHashMap. Otherwise, HashMap is probably best. It is typically faster and requires less overhead. This article is contributed by Mr.

Somesh Awasthi. If you like GeeksforGeeks and would like to contribute, you can also write an article using write. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Skip to content. Change Language. Related Articles. Table of Contents. Save Article. Improve Article. Like Article. We know that a Map is an object that represents a mapping from unique keys to values. Java offers several useful implementations of the java. This post provides an overview of some of the major differences between these implementations. HashMap ; import java. LinkedHashMap ; import java. Map ; import java. Download Run Code.

Assuming the hash method disperses the elements properly among the buckets, HashMap and LinkedHashMap offers O 1 time performance for the basic operations such as get, put, containsKey, remove, etc. So if performance is an issue, HashMap is preferred. Now coming to the space complexity, HashMap requires less memory than TreeMap and LinkedHashMap since it uses a hash table to store the mappings.

LinkedHashMap has the extra overhead of a doubly-linked list, and TreeMap is implemented as a Red-black tree, which takes more memory.

HashMap and LinkedHashMap permits null values and null key, whereas TreeMap permits only null values not null keys if the natural ordering of keys is used. It supports null keys only if its Comparator supports comparison on null keys.

The feature that distinguishes HashMap and LinkedHashMap from each other is that Hashmap does not maintain the order of the stored entries in a map. On the other hand, LinkedHashMap uses a hybrid data structure to maintain the order of entries in which they were inserted. Insertion order is preserved in LinkedHashMap. LinkedHashMap extends Hashmap. Overhead Comparatively less overhead. Comparatively more overhead because it has to maintain the order of the map entries.

HashMap is a class that is used to create a map. It implements Map Interface. It also extends the AbstractMap class so that it can use a hash table to store the entries in the map.

The key in the entry is used for retrieving the value hence, the key must be unique. But the key in the each entry of the map may have different type i. The data structure used by the HashMap to store a map is a hash table.