HashSet Vs LinkedHashSet in Java

Last Updated: 22 January, 2023

HashSet and LinkedHashSet are both implementations of the Set interface, contain unique elements, and accept only one NULL as an element. LinkedHashSet is a child class of the HashSet class.

There are many differences between the HashSet and LinkedHashSet that are given below.

👉 HashSet

The HashSet class is a member of the Java Collection Framework. HashSet was introduced in the JDK 1.2 version and is available in the java.util package.

A HashSet is used to create an unordered collection of elements that contains only unique elements; no duplicate elements are allowed. The HashSet provides constant-time performance for general operations such as add, remove, contain, size, etc.

HashSet's internal implementation is based on the hash table for creating and storing a collection of unique elements.

Java HashSet Class Declaration

public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, Serializable

Here, E defines the type of elements that the Set will contain.

Java HashSet important features:

A HashSet's underlying data structure is a hash table (an instance of HashMap).
A HashSet contains only unique elements, which means no duplicates are allowed.
In HashSet, elements are inserted based on their hash code, so no insertion order is preserved.
A HashSet can accept only one NULL element.
The initial capacity of the hash set is 16, and the load factor is.75.
By default, HashSet is not synchronized, which means multiple threads can access the same HashSet object at a time.
HashSet provides fast performance because it uses hashing techniques and gives constant-time performance.
HashSet is the best choice if we perform search operations.

👉 LinkedHashSet

The LinkedHashSet class of the Java collections framework was introduced in the JDK 1.4 version and is available in the java.util package.

LinkedHashSet is the Hashtable and linked list implementation of the Set interface with preserved iteration order. The linked list defines the iteration order, which is the order in which elements are inserted into the set. Insertion order is not affected if an element is re-inserted into the set.

LinkedHashSet is a child class of HashSet, so it has all the functionalities of the HashSet class. The HashSet does not maintain the insertion order of elements, whereas the LinkedHashSet maintains the element insertion order. This one is the main difference between both.

Java LinkedHashSet Class Declaration

public class LinkedHashSet<E> extends HashSet<E> implements Set<E>, Cloneable, Serializable

Here, E defines the type of elements that the Set will contain.

Java LinkedHashSet important features:

The underlying data structure is a hash table + linked list. It uses the implementation of a doubly-linked list on the hash table.
LinkedHashSet only stores unique elements; no duplicates are allowed.
LinkedHashSet maintains insertion order using a doubly linked list.
LinkedHashSet also supported inserting a single null value.
No new methods are added in the LinkedHashSet class; all are extended from HashSet.
LinkedHashSet is not synchronized.
Uses a hashing technique to store elements at the specified index based on the hashcode.
LinkedHashSet is the best choice to develop cache-based applications where duplicates are not allowed and insertion orders must be preserved.

👉 HashSet and LinkedHashSet have the following differences:

HashSet	LinkedHashSet
The underlying data structure is a hash table.	The underlying data structure is a hash table + linked list (doubly linked list).
Insertion order is not preserved.	Insertion order is preserved.
HashSet requires less memory than the LinkedHashSet.	LinkedHashSet requires more memory than the HashSet.
HashSet is a parent class of LinkedHashSet.	LinkedHashSet is a child class of HashSet.
Introduced in JDK 1.2 Version.	Introduced in JDK 1.4 Version.

👉 Example of HashSet and LinkedHashSet in Java

Example 1: A sample Java program of HashSet

  
  import java.util.HashSet;
  public class HashSetExample {
    public static void main(String[] args) {
      // Creating a HashSet
      HashSet<Integer> hashSet = new HashSet<Integer>();
      // Adding elements into the HashSet
      hashSet.add(800);
      hashSet.add(500);
      hashSet.add(null); // Adding null as an element
      hashSet.add(200);
      hashSet.add(500); // Adding duplicate element
      // Printing HashSet elements
      System.out.println("HashSet elements: " + hashSet);
    }
  }

Output

HashSet elements: [800, null, 500, 200]

Example 2: A sample Java program of LinkedHashSet

  
  import java.util.LinkedHashSet;
  public class LinkedHasSetExample {
    public static void main(String[] args) {
      // Creating a LinkedHashSet
      LinkedHashSet<Integer> linkedHashSet = new LinkedHashSet<Integer>();
        
      // Adding elements into the LinkedHashSet
      linkedHashSet.add(800);
      linkedHashSet.add(500);
      linkedHashSet.add(null); // Adding null as an element
      linkedHashSet.add(200);
      linkedHashSet.add(500); // Adding duplicate element will be ignored
      
      // Printing LinkedHashSet elements
      System.out.println("LinkedHashSet elements: " + linkedHashSet);
    }
  }

Output

LinkedHashSet elements: [800, 500, null, 200]

That's all guys, hope this Java article is helpful for you.

Happy Learning... 😀

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