HashMap vs HashSet: Difference and Comparison

HashMap and HashSet are two different functions in Hashtable. Hash table is nothing but a data structure where you can map the key values.

The hash function is the primary thing in Hashtable. The primary advantage of Hash table is speed when compared to other data structures.

Key Takeaways

1. HashMap is a data structure that stores key-value pairs, while HashSet stores unique elements without associated values.
2. HashMap implements the Map interface, and HashSet implements the Set interface in Java.
3. HashSet is backed by a HashMap, using dummy values for the keys to maintain a collection of unique elements.

HashMap vs HashSet

HashMap is a key-value based data structure that allows us to store and retrieve objects by using a unique key. HashSet is a set-based data structure that is used to store a collection of unique objects and uses hashing to store the objects and provides constant-time performance.

HashMap is associative of array data type. It is a part of the Java collection. This class can be found in Java until package.

This can be implemented in the map interface of Java, where it stores data in (KEY, VALUE), which is used to store the value and access it by key.

When we pass an object it can be accessed with a key value that is an index. We can ensure that duplicate key but which implies that previous element corresponding to the key.

The null keys are also get stored in HashMap. The HashMap allow only one null key.

A HashSet contain a unique collections. This class can be found in Java until package.

It uses its mechanism called hashing to store its information into a hash table, the element in the table is accessed by a unique value called hash code which is a class had implemented using a set interface underlying the data structure of the hash table.

It does not allow duplicate values but we can have dummy values. The main advantage is it can be a serializable and cloneable interface.

Comparison Table

Parameters of comparison	HashMap	HashSet
Dummy values	HashMap has no dummy values	HashSet has dummy values
Adding mechanism	HashMap uses hashing technique	HashSet uses hashing object
Speed	HashMap is faster	HashSet is slower
Insertion method	The insertion method in HashMap is Put()	The insertion method in HashSet is Add()
Example	(a-10, b-20, c-70)	(10,20,70)

What is HashMap?

Hashmap can be implemented by using the method (Hash Map<K, V> hm = new HashMap<K, V>();). A specified initial capacity and load factor can be created in HashMap for instance.

HashMap can sore values in different manners. It stores the string as key. In HashMap the key values are considered as objects. The primary task is to oragize the table using the kay values or objects. The time taken for organizing is O(1) time.

Because it is flexible Keys as a strength of the hash map. These are a similar to an array, but they have “indices” which are used to access the data, but in the hash map, we use Keys for accessing the Values.

There are some basic operations of HashMap like adding an element, accessing an element, changing an element, removing an element.

For adding an element, we use the put() method, For accessing an element, we use the get() method, For changing an element, we use replace() method, For removing an element use the remove() method.

Similarly, there are many commands and methods like clear, compute, merge, clone, size, etc, which are useful for the programmer to use the HashMap effectively.

What is HashSet?

HashSet can be implemented by syntax (Hash Set< E> hs = new Hash Set< E>();) which define the capacity of the hash set also without defining it default value will be 16 and load factor will be 0.75.

HashSet(int capacity, float fill Ratio) is used to resize the capacity of the hashset, when elements are greater it must have the capacity to store the value in the set, so the set is expanded.

We have the same basic operations like add, remove, contains, and size but it has and constant Time performance for this on basic operations.

Where in a set we have other various operations like union set, differences of the set, a subset has the advantage for the hashset method.

In the union of the set, we can perform union operation between two set by using the add-all() method. In the difference of set, we can calculate the difference between two set by using the remove-all() method.

In Subset, we can add another subset of another set by using contains-all() method. When we are adding values or inserting the value in the HashSet it cannot be in order it is inserted on the basis of code.

Iteration to elements is returned in no particular order. We can also use the Index at which the data associated with the key is stored.

Mostly we can use hashset for accessing a random element from their set. Because it is accessed through hash code, where it is unique so we can identify the element easily.

As it is not unsynchronized, multiple threats can be accessed at the same time and can be modified. It is accomplished by synchronizing one object in the set.

The values in an asset or actually an object we can create an object of type string and can be wrapped into class we specify. Where it stores integer as an object to limit the time complexity.

Main Differences Between HashMap and HashSet

1. The object requirement during addition in HashMap is two, whereas in HashSet the object requirement during addition is only one.
2. HashMap has any number of null values, but HashSet has only a single null value.
3. The key-value pair is stored in HashMap, whereas objects are stored in HashSet.
4. When compared to Hashmap, HashSet is used for the uniqueness of data.
5. Example for HashMap is {a->4, b->9, c->5}, and example for HashSet is {6, 43, 2, 90, 4}.

References

1. https://dl.acm.org/doi/abs/10.1145/2884781.2884869?casa_token=1z9VmoTZC90AAAAA:8-pUqjpp5C0S4rIzg2sMUI4FeuvVH5QIN99WkbSrP1HSwCa13CtZa7lXBKMzm864NI__H8iKBcjMZck
2. https://ieeexplore.ieee.org/abstract/document/5370764/

Last Updated : 13 July, 2023