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HashMap vs. HashSet: Know the Difference

Shumaila Saeed
By Shumaila Saeed || Published on February 16, 2024
HashMap is a data structure using key-value pairs for efficient data retrieval; HashSet is a collection that stores unique elements without duplicates.
HashMap vs. HashSet

Key Differences

HashMap is a data structure that implements the Map interface in Java, allowing for the storage and retrieval of key-value pairs. This facilitates quick lookup, addition, and deletion of data based on the key. HashSet, on the other hand, implements the Set interface and is primarily used for storing unique elements, ensuring that no two items are identical.
Shumaila Saeed
Shumaila Saeed
Feb 16, 2024
In a HashMap, each key maps to a specific value, and one can retrieve a value by providing its associated key. This association makes HashMap ideal for scenarios where key-based data access is required. HashSet does not store key-value pairs; instead, it only stores individual elements, focusing on the uniqueness of each item in the collection.
Shumaila Saeed
Shumaila Saeed
Feb 16, 2024
HashMap allows for duplicate values but insists on unique keys; no two keys can be the same. This uniqueness of keys is a fundamental feature of HashMap. Conversely, HashSet is all about unique elements and does not allow any duplicates within its collection, making it suitable for tasks like removing duplicates from a list.
Shumaila Saeed
Shumaila Saeed
Feb 16, 2024
The performance of HashMap is generally considered in terms of its get and put operations, which are typically efficient due to the hashing mechanism. HashSet’s performance is measured by its ability to quickly determine whether an element is present in the set, which is also powered by an underlying hash table.
Shumaila Saeed
Shumaila Saeed
Feb 16, 2024
HashMap provides methods to work with key-value pairs, like put(), get(), remove(), and iterators that allow traversal over keys, values, or both. HashSet offers methods like add(), remove(), contains(), and an iterator that traverses through the elements in the set.
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Comparison Chart

Data Structure Type

Map
Set
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Feb 16, 2024

Storage Mechanism

Stores key-value pairs
Stores individual elements
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Uniqueness

Keys must be unique
All elements must be unique
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Duplicate Values

Allows duplicate values
Does not allow duplicate elements
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Primary Operations

Put(), get(), remove()
Add(), remove(), contains()
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Use Case

Retrieving data by key
Storing unique items
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HashMap and HashSet Definitions

HashMap

HashMap allows null values and one null key.
Our system's configuration settings were stored in a HashMap, including a null key for the default setting.
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HashSet

HashSet is a set-based collection used to store unique elements.
We used a HashSet to maintain a list of unique visitor IDs.
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HashMap

It's part of Java's Collections Framework, often used in programming.
We optimized our data processing by implementing a HashMap for temporary storage.
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Jan 24, 2024

HashSet

It prevents the storage of duplicate values in a collection.
To avoid duplicate entries, we stored the data in a HashSet.
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HashMap

HashMap is a map-based collection that stores elements as key-value pairs.
In our application, we used a HashMap to store user IDs and their corresponding names.
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HashSet

HashSet offers efficient operations like add, remove, and contains.
The HashSet was used to quickly check if a username already exists.
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HashMap

It's an efficient way to store and retrieve data based on unique keys.
To speed up searches, we utilized a HashMap with product codes as keys.
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HashSet

It's part of the Java Collections Framework, ideal for uniqueness constraints.
Our system used a HashSet to ensure each serial number was used only once.
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HashMap

HashMap employs hashing for storing and accessing data.
The employee database was implemented using a HashMap for quick access.
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HashSet

HashSet uses a hash table for storage, ensuring fast access.
For quick member verification, we stored the member IDs in a HashSet.
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HashMap

Alternative spelling of hash map
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Repeatedly Asked Queries

Are null values allowed in a HashMap?

Yes, HashMap can store null values and one null key.
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Is HashMap ordered?

No, HashMap does not maintain the order of its elements.
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What is a HashSet?

A collection that stores a set of unique elements.
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Is HashSet ordered?

No, elements in a HashSet are not stored in any particular order.
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Can a HashMap contain duplicate keys?

No, keys in a HashMap must be unique.
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What is a HashMap?

A data structure for storing key-value pairs, allowing efficient retrieval.
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Feb 16, 2024

Can HashSet store duplicate elements?

No, HashSet does not allow duplicates.
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What are common use cases for HashMap?

HashMap is used for caching, lookup tables, and associative arrays.
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How does HashMap handle collisions?

HashMap handles collisions using a linked list or tree structure within each bucket.
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Is HashSet thread-safe?

No, HashSet is not thread-safe by default.
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What is the initial capacity of a HashMap?

The default initial capacity is 16.
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What are common use cases for HashSet?

HashSet is used for maintaining unique collections and filtering duplicates.
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Which is faster, HashMap or HashSet?

Performance depends on the use case, but both are generally efficient due to hashing.
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Can HashMap be synchronized?

Yes, using Collections.synchronizedMap or ConcurrentHashMap.
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How does HashSet determine uniqueness?

HashSet uses the hashCode() and equals() methods to determine uniqueness.
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Can HashSet contain null values?

Yes, HashSet can contain a single null element.
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How do you iterate over a HashMap?

By using iterators over keySet, entrySet, or values.
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How is HashMap different from HashSet?

HashMap stores key-value pairs, while HashSet stores only unique elements.
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Shumaila Saeed
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How do you iterate over a HashSet?

By using an iterator over the set.
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What is the load factor in HashMap?

The load factor, typically 0.75, determines when the map is resized.
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Feb 16, 2024

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About Author
Shumaila Saeed
Written by
Shumaila Saeed
Shumaila Saeed, an expert content creator with 6 years of experience, specializes in distilling complex topics into easily digestible comparisons, shining a light on the nuances that both inform and educate readers with clarity and accuracy.

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