The HashSet in Java is a distinct collection that retains solely unique items. It does not preserve sequence, but it is extremely efficient when it comes to adding, retrieving, or removing elements. It employs a hashing mechanism to quickly locate items. HashSet proves advantageous when you wish to circumvent duplicates and have no concern for the arrangement of elements.
This article will provide an in-depth exploration of the HashSet, including its features and constraints.
HashSet is a specific class in Java employed to hold a collection of distinct elements. It is part of the Java Collections Framework and resides in the java.util package.
The term HashSet consists of two components: Hash and Set, signifying the following:
Hash: It utilizes hashing techniques to store elements, facilitating rapid operations such as search, insertion, and deletion.
Set: It refers to a mathematical set that contains unique elements, without maintaining the sequence of the stored items.
Hierarchy of HashSet
The diagram above illustrates a detailed representation of the HashSet hierarchy, which we will briefly discuss below.
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractSet<E>
java.util.HashSet<E>
Let’s delve into each layer in detail.
1. Object
This is the fundamental class of all Java Classes. Every Java class inherits directly or indirectly from Object.
2. AbstractCollection<E>
This provides the foundational implementation for methods in the Collection interface.
3. AbstractSet<E>
This guarantees that sets do not permit duplicate elements.
4. HashSet<E>
This class extends AbstractSet and provides a comprehensive implementation of the Set interface using a hash table.
In Java, a HashSet can be declared using the HashSet class from the java.util package. Below is a detailed explanation of this process.
Syntax:
HashSet<Type> setName = new HashSet<>();
Let’s illustrate this with an example.
Example:
Java
Code Copied!
var isMobile = window.innerWidth “);
editor41327.setValue(decodedContent); // Set the default text
editor41327.clearSelection();
editor41327.setOptions({
maxLines: Infinity
});
function decodeHTML41327(input) {
var doc = new DOMParser().parseFromString(input, “text/html”);
// Additional processing if necessary
}
“““javascript
return doc.documentElement.textContent;
}
// Function to duplicate code to clipboard
function duplicateCodeToClipboard41327() {
const code = editor41327.getValue(); // Retrieve code from the editor
navigator.clipboard.writeText(code).then(() => {
// alert(“Code duplicated to clipboard!”);
data: {
language: “java”,
code: code,
cmd_line_args: “”,
variablenames: “”,
action:”compilerajax”
},
success: function(response) {
var myArray = response.split(“~”);
var data = myArray[1];
jQuery(“.output41327”).html(“
"+data+"");
jQuery(".maineditor41327 .code-editor-output").show();
jQuery("#runBtn41327 i.run-code").hide();
}
})
}
function hideOutput41327() {
var code = editor41327.getSession().getValue();
jQuery(".maineditor41327 .code-editor-output").hide();
}
// Attach event listeners to the buttons
document.getElementById("copyBtn41327").addEventListener("click", duplicateCodeToClipboard41327);
document.getElementById("runBtn41327").addEventListener("click", executeCode41327);
document.getElementById("closeoutputBtn41327").addEventListener("click", hideOutput41327);
Result:
Clarification:
In the aforementioned Java example, a HashSet of type String is utilized, in which the element Java is used twice, but only one instance will be incorporated. Additionally, a null value is included.
Internal Functioning of HashSet
Before proceeding, let's examine how the HashSet operates. HashSet implements the following mechanism to preserve its elements.
1. Calculate the Hash Code
When an element is introduced into the HashSet, it initially invokes the hashCode() method of that object.
2. Implement Hashing
In this phase, the bucket index is searched for where an element can be accommodated. Buckets resemble slots within an array, where each element is held.
3. Verify Duplicates using equals()
At this stage, if any other element is already situated in that bucket, it employs the equals() method to ascertain whether the elements are identical.
Should equals() return true, the element is classified as a duplicate and is not added to the HashSet.
4. Insert into Map
HashSet internally utilizes a HashMap where the key represents the element, and the value is a constant placeholder object, commonly referred to as PRESENT.
Constructors of the HashSet Class
Constructor
Description
HashSet()
Creates an empty HashSet with default initial capacity (16) and load factor (0.75)
HashSet(int initialCapacity)
Creates an empty HashSet with specified initial capacity and default load factor (0.75)
HashSet(int initialCapacity, float loadFactor)
Creates an empty HashSet with specified initial capacity and load factor
HashSet(Collection<? extends E> c)
Creates a HashSet containing elements from the specified collection (duplicates are removed)
Methods in Java HashSet
Attribute
BufferedReader
Scanner
Speed
Quicker (utilizes buffering)
Slower (token-based)
User-Friendliness
Requires manual conversion
Simple to utilize
Data Reading
Only strings (conversion needed)
Strings, numbers, boolean values
Optimal Usage
Large files, performance-centric
General user input
Error Management
Requires try-catch (IOException)
Built-in error management
Memory Footprint
Minimal (utilizes buffering)
Higher (processes input)
Functions
readLine()
nextInt(), nextLine(), nextDouble(), etc.
Executing Various Operations on HashSet
1. Inserting Elements into HashSet
For adding elements to a HashSet in Java, you can utilize the add() method to introduce an element. If you attempt to add a duplicate element, it will be disregarded.
Sample:
Java
Code Duplicated!
Output:
Explanation:
The Java code presented above demonstrates how elements are added to the HashSet. Duplicate items are disregarded, ensuring that only unique items are retained.
2. Deleting Elements in HashSet
To eliminate a specific element from a HashSet in Java, utilize the remove() method. For erasing all elements, the clear() method can be employed.
Example:
Java
Code Copied!
Output:
``````html
Clarification:
In the preceding Java code, initially, elements are added to the HashSet. Subsequently, the element 20 is eliminated from it utilizing the .remove method, followed by the use of the .clear method to delete all the items from the hash set.
3. Traversing through the HashSet
You can utilize a for-each loop or an iterator for navigating through a HashSet.
function closeoutput21716() {
jQuery(".maineditor21716 .code-editor-output").hide();
}
// Attach event listeners to the buttons
document.getElementById("copyBtn21716").addEventListener("click", copyCodeToClipboard21716);
document.getElementById("runBtn21716").addEventListener("click", runCode21716);
document.getElementById("closeoutputBtn21716").addEventListener("click", closeoutput21716);
Result:
Clarification:
In the aforementioned Java code, the HashSet is traversed using the for-each loop and subsequently by employing the iterator.
Performance of HashSet
HashSet is efficient as it does not examine each item individually but instead directly accesses the appropriate element using the hash code of that item, which accelerates operations like addition and deletion.
Primary operations in the HashSet and their speed
Characteristic
BufferedReader
Scanner
Speed
Quicker (employs buffering)
Slower (token-based)
User-Friendliness
Needs manual conversion
Simple to use
Data Reading
Only strings (requires conversion)
Strings, numbers, booleans
Optimal For
Large files, performance
General user input
Exception Management
Requires try-catch (IOException)
In-built exception handling
Memory Consumption
Low (utilizes buffering)
Higher (parses input)
Methods
readLine()
nextInt(), nextLine(), nextDouble(), etc.
Note:O(1) signifies that the time taken does not escalate even if there are 100 or 1000 items. However, it may sometimes become sluggish, i.e., O(n), if multiple items are assigned to the same bucket.
Load factor is a determinant that indicates when to augment the capacity of the HashSet. It represents the ratio of the number of elements to the bucket size before resizing. The default load factor value in Java is 75%, meaning when the count of stored elements in the HashSet reaches 75% of...
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Once the overall capacity is reached, the HashSet will expand itself, similarly doubling its size to alleviate congestion.
The greater the load factor, the less memory is utilized, resulting in it becoming slower. Conversely, the lower the load factor, the more memory is consumed, and the faster the operation becomes.
A HashSet begins with a predetermined number of buckets. When the HashSet reaches capacity, it generates a larger storage space and relocates all entries to the new buckets. This action is referred to as resizing, which typically takes about O(n) time.
If you anticipate needing to save numerous entries, you should preset the size of the HashSet to a higher value, such as
HashSet<String> set = new HashSet<>(1000);
The HashSet may occasionally perform slowly due to the following factors.
1. If various elements produce identical hash codes, they will be placed on the same shelf, leading to extended search times.
2. If the HashSet contains more entries than anticipated, it will resize itself, which is a time-consuming process.
3. The hash code function must consistently yield a distinct value; otherwise, all items may converge into a single bucket, slowing down the search.
Attributes of HashSet in Java
HashSet in Java presents several features. Some of these include:
1. Framework: It is a component of the Java Collection Framework.
2. Implements Set Interface: It adheres to the Set interface.
3. Backed by HashMap: HashSet utilizes HashMap internally, used to hold unique values within the HashSet. This grants efficient performance for various operations such as addition, removal, and more.
4. No Guaranteed Order: HashSet does not preserve the sequence of the stored values. The values are arranged based on their hash code values.
5. Allows Null Elements: HashSet permits a single null value to be stored within it.
6. Non-Synchronized: HashSet is not synchronized, meaning it is not thread-safe by default.
7. Efficient Performance: It offers constant time performance for most operations, including Add(), remove(), and contains().
8. Generic Compatibility: Similar to other collections, HashSet supports generics, enabling you to restrict the types of elements. This enhances type safety.
HashSet vs. ArrayList vs. HashMap vs. TreeSet
Feature
HashSet
ArrayList
HashMap
TreeSet
Based on
HashMap
Dynamic Array
Hash Table
Red-Black Tree
Duplicates Allowed
No
Yes
Not for keys, only for values
No
Order Maintained
No
Yes, insertion order
No
Yes, sorted order
Allows Null
only one
multiple
One null key, many null values
only one, if allowed
Search Time
O(1)
O(n)
O(1)
O(log n)
Thread Safe
No
No
No
No
Use Case
Store unique items
Store an ordered list with duplicates
Store key-value pairs
Store sorted unique items
Best Practices for Using HashSet
1. Use a HashSet only when it's necessary to store distinct elements.
2. If you are storing custom objects within the HashSet, be sure to override both equals() and hashCode() to guarantee accurate duplicate detection.
3. If you have an estimated number of elements to be stored in the HashSet, initialize its capacity accordingly to prevent resizing.
4. Utilize the contains() method to verify the existence of an element in the HashSet.
5. Given that a HashSet permits only one null value, attempting to store multiple nulls may cause confusion.
Limitations of HashSet and When Not to Use It
1. HashSet does not preserve the order of elements, which means the insertion sequence is not maintained. Avoid using HashSet if maintaining the insertion order is crucial.
2. Accessing the HashSet from multiple threads without synchronization can lead to unpredictable behavior.
3. The efficiency of the HashSet is directly influenced by the hashCode(), potentially causing issues such as undetected duplicate elements.
4. Avoid employing the HashSet if you require storage of elements in a sorted arrangement.
5. Refrain from using HashSet when memory consumption is a critical concern.
HashSet is a method for storing distinct elements in Java. It is quick, user-friendly, and prohibits duplicate values. It does not maintain the order of elements and only allows one null entry. It performs well when rapid retrieval is needed without regard for element order. HashSet utilizes HashMap internally for element storage. It should be utilized primarily when uniqueness is essential. Being part of the Java Collections Framework, it is frequently employed in everyday programming.
For further exploration on this topic, refer to our Java course.
HashSet in Java – FAQs
Q1. What is the distinction between HashMap and HashSet?
HashMap organizes data in pairs, consisting of keys and values, whereas HashSet exclusively retains individual unique items.
Q2. What separates a Set from a HashSet?
Set serves as a broader category that represents an unordered collection of unique elements.
``````html
is an interface, whereas HashSet serves as its implementation utilizing a hash table.
Q3. Is HashSet more rapid than HashMap?
Indeed, HashSet may perform slightly quicker if your goal is merely to store distinct values.
Q4. Is it possible for a HashSet to contain duplicates?
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