LinkedHashSet in Java

LinkedHashSet in Java implements the Set interface of the Collections Framework.

• It combines the functionalities of a HashSet with a doubly-linked list to maintain the insertion order of elements.
• LinkedHashSet stores unique elements only and allows a single null.
• Implements Set, Cloneable and Serializable interfaces.

import java.util.LinkedHashSet; public class Geeks {  public static void main(String[] args) {    // Create a LinkedHashSet of Strings  LinkedHashSet<String> set = new LinkedHashSet<>();  set.add("Apple");  set.add("Banana");  set.add("Cherry");  set.add("Apple");  System.out.println("" + set);  } } 

[Apple, Banana, Cherry] 

Hierarchy of LinkedHashSet

It implements the Set interface, which is a sub-interface of the Collection interface.

Constructors of LinkedHashSet

1. LinkedHashSet()

This constructor is used to create an empty LinkedHashSet with the default capacity i.e. 16 and load factor 0.75.

LinkedHashSet<E> hs = new LinkedHashSet<E>();

2. LinkedHashSet(Collection C)

Used in initializing the LinkedHashSet with the elements of the collection C.

LinkedHashSet<E> hs = new LinkedHashSet<E>(Collection c);

3. LinkedHashSet(int initialCapacity)

Used to initialize the size of the LinkedHashSet with the integer mentioned in the parameter.

LinkedHashSet<E> hs = new LinkedHashSet<E>((int initialCapacity);

4. LinkedHashSet(int capacity, float fillRatio)

Creates an empty LinkedHashSet with specified capacity and load factor.

LinkedHashSet<E> hs = new LinkedHashSet<E>(int capacity, float loadFactor);

Performing Various Operations on LinkedHashSet

Let’s see how to perform a few frequently used operations on the LinkedHashSet.

1. Adding Elements in LinkedHashSet

In order to add an element to the LinkedHashSet, we can use the add() method. This is different from HashSet because in HashSet, the insertion order is not retained but is retained in the LinkedHashSet.

import java.io.*; import java.util.*; class Geeks {  public static void main(String[] args) {  // Creating an empty LinkedHashSet  LinkedHashSet<String> lh = new LinkedHashSet<String>();  // Adding elements to above Set using add() method  lh.add("Geek");  lh.add("For");  lh.add("Geeks");  System.out.println("LinkedHashSet : " + lh);  } } 

LinkedHashSet : [Geek, For, Geeks] 

2. Removing Elements in LinkedHashSet

The values can be removed from the LinkedHashSet using the remove() method.

import java.io.*; import java.util.*; class Geeks {  public static void main(String[] args) {  // Creating an empty LinekdhashSet of string type  LinkedHashSet<String> lh  = new LinkedHashSet<String>();  // Adding elements to above Set using add() method  lh.add("Geek");  lh.add("For");  lh.add("Geeks");  lh.add("A");  lh.add("B");  lh.add("Z");  System.out.println("" + lh);  // Removing the element from above Set  lh.remove("B");  // Again removing the element  System.out.println("After removing element " + lh);  // Returning false if the element is not present  System.out.println(lh.remove("AC"));  } } 

[Geek, For, Geeks, A, B, Z] After removing element [Geek, For, Geeks, A, Z] false 

3. Iterating through the LinkedHashSet

Iterate through the elements of  LinkedHashSet usingthe iterator() method. The most famous one is to use the enhanced for loop.

import java.io.*; import java.util.*; class Geeks {  public static void main(String[] args) {  Set<String> lh = new LinkedHashSet<String>();  lh.add("Geek");  lh.add("For");  lh.add("Geeks");  lh.add("A");  lh.add("B");  lh.add("Z");  Iterator itr = lh.iterator();  while (itr.hasNext())  System.out.print(itr.next() + ", ");  System.out.println();  for (String s : lh)  System.out.print(s + ", ");  System.out.println();  } } 

Geek, For, Geeks, A, B, Z, Geek, For, Geeks, A, B, Z, 

Methods of LinkedHashSet

Suggested Quiz

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3 Questions

What is the difference between LinkedHashSet and HashSet?

• A

  Both store's nonduplicates values

• B

  Both implements the AbstractSet interface

• C

  The order of elements is maintained in LinkedHashSet, not in the HashSet

• D

  None of the above

Explanation:

HashSet is an unordered & unsorted collection of the data set, whereas the LinkedHashSet is an ordered and sorted collection of HashSet. 

Which of the following is true about LinkedHashSet?

• A

  It allows duplicate elements

• B

  It maintains insertion order

• C

  It sorts elements in ascending order

• D

  It does not use hashing

Explanation:

LinkedHashSet maintains the insertion order while still using hashing internally.

LinkedHashSet internally uses which data structure?

• A

  HashMap + TreeMap

• B

  HashMap + LinkedList

• C

  Hashtable

• D

  ArrayList

Explanation:

A LinkedHashSet uses a HashMap with a doubly-linked list to maintain order.

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