Which is better treemap or hashmap

Data Mining. Data Warehouse. Javatpoint Services JavaTpoint offers too many high quality services. HashMap contains value based on the key.

It may have a single null key and multiple null values. HashMap does not maintain order while iterating. It contains unique elements. It works on the principle of hashing. TreeMap also contains value based on the key. TreeMap is sorted by keys. It cannot have a null key but have multiple null values. Keys are in ascending order. It stores the object in the tree structure. A Map is an object which stores key-value pairs. In the key-value pair, each key is unique, but their values may be duplicate.

Both classes represents the mapping from key to values. Both maps are not synchronized. From the output, it is observed that keys are sorted in a natural order. Hence Treemap maintains sorted order. Hash Map is a hash table-based implementation. It extends the Abstract Map class and implements the Map interface. A Hash Map works on the principle of hashing.

The Map implementation acts as a bucketed hash table, but when buckets get too large in size, they get converted into Tree nodes, each having a similar structure to the nodes of TreeMap. The underlying data structure for the treemap is a Red-Black tree. The Iteration order of Hash Map is undefined, whereas elements of a TreeMap are ordered in natural order or in a custom order specified using a comparator.

As Hashmap is a hashtable based implementation, it provides constant-time performance that is equal to O 1 for most of the common operations. The time required to search an element in a hash map is O 1.

But if there is an improper implementation in hashmap, then this may lead to additional memory overhead and performance degradation. 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.

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Skip to content. Change Language. Related Articles. 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.