LinkedHashSet in Java with Examples

A LinkedHashSet is an ordered version of HashSet that maintains a doubly-linked List across all elements. When the iteration order is needed to be maintained this class is used. When iterating through a HashSet the order is unpredictable, while a LinkedHashSet lets us iterate through the elements in the order in which they were inserted. When cycling through LinkedHashSet using an iterator, the elements will be returned in the order in which they were inserted.

Syntax:

LinkedHashSet<String> hs = new LinkedHashSet<String>();
  • Contains unique elements only like HashSet. It extends HashSet class and implements Set interface.
  • Maintains insertion order.

Given below are the list of constructors supported by the LinkedHashSet:

  1. HashSet(): This constructor is used to create a default HashSet.
  2. HashSet(Collection C): Used in initializing the HashSet with the eleements of the collection C
  3. LinkedHashSet(int size): Used to intialize the size of the LinkedHashSet with the integer mentioned in the parameter.
  4. LinkedHashSet(int capacity, float fillRatio): Can be used to initialize both the capacity and the fill ratio, also called the load capacity of the LinkedHashSet with the arguments mentioned in the parameter. When the number of elements exceeds the capacity of the hash set is multiplied with the fill ratio thus expanding the capacity of the LinkedHashSet


Below program explains the basic add and traversal operation of LinkedHashSet:

import java.util.LinkedHashSet;  
public class Demo 
{  
    public static void main(String[] args) 
    {  
        LinkedHashSet<String> linkedset = 
                           new LinkedHashSet<String>();  
  
        // Adding element to LinkedHashSet  
        linkedset.add("A");  
        linkedset.add("B");  
        linkedset.add("C");  
        linkedset.add("D"); 
  
        // This will not add new element as A already exists 
        linkedset.add("A"); 
        linkedset.add("E");  
  
        System.out.println("Size of LinkedHashSet = " +
                                    linkedset.size());  
        System.out.println("Original LinkedHashSet:" + linkedset);  
        System.out.println("Removing D from LinkedHashSet: " +
                            linkedset.remove("D"));  
        System.out.println("Trying to Remove Z which is not "+
                            "present: " + linkedset.remove("Z"));  
        System.out.println("Checking if A is present="
                            linkedset.contains("A"));
        System.out.println("Updated LinkedHashSet: " + linkedset);  
    }  
}  


Output:



Size of LinkedHashSet=5
Original LinkedHashSet:[A, B, C, D, E]
Removing D from LinkedHashSet: true
Trying to Remove Z which is not present: false
Checking if A is present=true
Updated LinkedHashSet: [A, B, C, E]

Following is the difference between LinkedHashMap and LinekdHashSet:

Important : Keeping the insertion order in both LinkedHashmap and LinkedHashset have additional associated costs, both in terms of spending additional CPU cycles and needing more memory. If you do not need the insertion order maintained, it is recommended to use the lighter-weight HashSet and HashMap instead.



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Improved By : Chinmoy Lenka