The Java Collections framework's classes include Java HashMap and TreeMap.
A collection, often known as a container, is just an object that unifies several items into one. Aggregate data is stored, retrieved, handled, and communicated via collections. The typical Java Map implementation functions as a hash table with buckets. When buckets grow too big, they are converted into TreeNode nodes, each of which has a structure akin to that found in java.util. TreeMap.
What is HashMap?
HashMap is a data structure that stores items using "key-value" pairs. They are great at mapping, as the name would imply. We can map one object to another using hash maps. It could be a multi-fielded object, a String, or an integer. It is a crucial data structure, and Java offers its implementation.
Key and value pairs are found in maps. HashMap is a hashtable-based implementation of the Map interface, which is available in Java. Java's HashMap class is virtually identical to Hashtable, except that it is unsynchronized and supports nulls. Basic operations like insertion and deletion are performed in constant time by HashMap.
Syntax of HashMap in Java:
HashMap<K, V> h = new HashMap<K, V>();
What is TreeMap?
A well-known data structure for organizing and displaying hierarchical data is a tree. It consists of a group of items, referred to as nodes, that are connected non-linearly. A self-balancing binary search tree known as a red-black tree requires that every path from a node to any of its descendent null nodes contain an equal number of black nodes.
A red-black tree-based NavigableMap implementation is known as a TreeMap. The SortedMap class is extended by the Navigable Map Interface, a component of the Java Collections framework, which offers practical navigation methods for navigating a map. The Map interface and the AbstractMap class are both implemented by TreeMap.
Here are some of the similarities between HashMap and TreeMap. Learning similarities between them is equally important as learning the difference between hashMap and treeMap.
In terms of
HashMap and TreeMap
Class Extension,
Both extend AbstractMap<K, V> Class.
Synchronization
Both data structures are not synchronized.
Cloneablity and Serializability
Both data structures implement a Cloneable and Serializable interface.
Methods
Both use the put() method to insert an element.
Iterator
In case of modification, both throws ConcurrentModificationException.
Data Storage
Both store data in key-value format. HashMap does not support duplicate keys, nor does TreeMap. It replaces the previous element if it is added (without an error or an exception)
One of the major difference between hashMap and TreeMap is, While TreeMap uses a comparator set in its constructor or the compareTo() method to preserve the sequence of iterations, HashMap does not.
Here are the main areas where hashmap and treemap differ:
In terms of
HashMap
TreeMap
Definition
A hashtable-based implementation of the Map interface is called Java HashMap.
Java TreeMap implements the Map interface using a Tree structure.
Internal Implementation
Since HashMap is a hashtable-based implementation, its internal element organization is based on an array-based data structure.
A TreeMap can sort its items using a custom Comparator and keeps its data in a hierarchical tree.
Storage
The default behavior of this Map implementation is a bucketed hash table, but when buckets grow too big, they are converted into nodes of TreeNodes, each of which has a structure akin to that in java.util. TreeMap.
Red-Black trees, which are Self-Balancing Binary Search Trees, are used by TreeMaps to store map elements.
Order
The arrangement of the components in the Map is not guaranteed by HashMap.
A TreeMap sorts its objects in the order that they naturally appear.
Null Values
At most one null key and numerous null values may be stored in a hash map.
While TreeMap forbids a null key, it does permit several null values.
Performace
For most operations like add(), delete(), and contain(), HashMap delivers expected constant-time performance O(1).
When performing most operations like add(), delete(), and contains(), TreeMap offers a performance of O(log(n)).
Interface
HashMap implements the Map interface.
TreeMap implements the NavigableMap interface
Functions
HashMap has limited functions.
TreeMap contains functions like pollFirstEntry(), pollLastEntry(), tailMap(), firstKey(), lastKey(), etc.
Compare function
To compare keys, it makes use of the Object class' equals() function. It is superseded by the equals() function of the Map class.
To compare keys, it makes use of the compareTo() method.
Homogeneous / Hetrogeneous
Because HashMap does not conduct sorting on keys, it permits heterogeneous elements.
Because of sorting, TreeMap accepts homogenous values as a key.
Implemented Interfaces,
It implements Serializable, Clonable, and Map interfaces.
It implements Serializable, Clonable, and NavigableMap interfaces.
Prefer using treeMap over hashmap when:
Instead of unordered elements, sorted elements are needed. TreeMap's sorted list is always returned in ascending order.
To arrange the elements, TreeMap employs the Red-Black algorithm. TreeMap is a suitable option when one needs to do often read/write operations.
Memory restrictions must be taken into account.
We want to extract objects in a natural sequence if items will be continuously added and withdrawn, but we don't know how many items must be held in memory.
Frequently Asked Questions
What is the purpose of TreeMap?
Its method for visualizing big, hierarchical data sets uses treemaps. They record two different sorts of data: the hierarchy's structure and the value of each data point.
What is HashMap in Java?
Since Java 1.2, HashMap<K, V> has been a component of the Java collection. The java.util package contains this class. It offers the rudimentary Java Map interface implementation.
What does HashMap's bucket mean?
A component of the HashMap array is a bucket. Nodes are kept there. The same bucket may be shared by two or more nodes.
How does HashMap store null keys?
Hashmap allows for both multiple null values and one null key. Since the hashcode for null is 0, the hashmap stores the null key at index 0.
Conclusion
This article covers everything you need to know about the Difference between hashmap and treemap. We hope this on the Difference between hashmap and treemap helps you in your journey.
116+ registered 