In this article, we will discuss how to sort contents of LinkedHashSet

Key points about LinkedList:

• LinkedHashSet maintains insertion-order
• as it uses doubly-linked list and hash table to store element/objects

 

Different ways to sort LinkedHashSet :

1. Convert LinkedHashSet to TreeSet for natural-ordering
2. Convert LinkedHashSet to TreeSet for reverse-ordering by providing Comparator based customized-sorting logic
3. Using ArrayList and Collections class’ utility method sort();

Let us move forward to discuss different ways to sort LinkedHashSet contents

 

Way 1: Convert LinkedHashSet to TreeSet for natural-ordering

Steps:

• Create new LinkedHashSet object
• Store/add contents to LinkedHashSet
• Create new TreeSet object,
• Pass LinkedHashSet contents as argument to TreeSet’ inter-conversion constructor

Syntax:

// convert LinkedHashSet to TreeSet
TreeSet<String> tSet = new TreeSet<String>(lhsCompanies); 

SortingLinkedHashSetUsingTreeSet.java

package in.bench.resources.collection;

import java.util.LinkedHashSet;
import java.util.TreeSet;

public class SortingLinkedHashSetUsingTreeSet {

	public static void main(String[] args) {

		// creating LinkedHashSet object of type String
		LinkedHashSet<String> lhsCompanies = 
				new LinkedHashSet<String>();

		// adding elements to LinkedHashSet object
		lhsCompanies.add("LinkedIn");
		lhsCompanies.add("Amazon");
		lhsCompanies.add("Google");
		lhsCompanies.add("Apple");
		lhsCompanies.add("Facebook");
		lhsCompanies.add("Oracle");
		lhsCompanies.add("Microsoft");

		// Iterating using enhanced for-loop
		System.out.println("Insertion Order:"
				+ " Iterating LinkedHashSet\n");
		for(String company : lhsCompanies) {
			System.out.println(company);
		}

		// convert LinkedHashSet to TreeSet
		TreeSet<String> tSet = new TreeSet<String>(lhsCompanies); 

		// Iterating using enhanced for-loop
		System.out.println("\n\nAscending sorting-order:"
				+ " Iterating TreeSet\n");
		for(String company : tSet) {
			System.out.println(company);
		}
	}
}

Output:

Insertion Order: Iterating LinkedHashSet

LinkedIn
Amazon
Google
Apple
Facebook
Oracle
Microsoft


Ascending sorting-order: Iterating TreeSet

Amazon
Apple
Facebook
Google
LinkedIn
Microsoft
Oracle

 

Way 2: Convert LinkedHashSet to TreeSet for reverse-ordering

Steps:

• Create new LinkedHashSet object
• Store/add contents to LinkedHashSet
• Create new TreeSet object and provide reverse-order sorting-logic using Comparator
• Add LinkedHashSet contents  to TreeSet using addAll(); method

Syntax:

// create new TreeSet object and provide reverse-sorting logic
		TreeSet<String> tSet = new TreeSet<String>(
				new Comparator<String>() {

					@Override
					public int compare(String str1, String str2) {
						return str2.compareTo(str1);
					}
				}); 

		// add LinkedHashSet to TreeSet for reverse-sorting elements
		tSet.addAll(lhsCompanies);

ReverseSortingLinkedHashSetUsingTreeSet.java

package in.bench.resources.collection;

import java.util.Comparator;
import java.util.LinkedHashSet;
import java.util.TreeSet;

public class ReverseSortingLinkedHashSetUsingTreeSet {

	public static void main(String[] args) {

		// creating LinkedHashSet object of type String
		LinkedHashSet<String> lhsCompanies = 
				new LinkedHashSet<String>();

		// adding elements to LinkedHashSet object
		lhsCompanies.add("LinkedIn");
		lhsCompanies.add("Amazon");
		lhsCompanies.add("Google");
		lhsCompanies.add("Apple");
		lhsCompanies.add("Facebook");
		lhsCompanies.add("Oracle");
		lhsCompanies.add("Microsoft");

		// Iterating using enhanced for-loop
		System.out.println("Insertion Order:"
				+ " Iterating LinkedHashSet\n");
		for(String company : lhsCompanies) {
			System.out.println(company);
		}

		// create new TreeSet object and provide reverse-sorting logic
		TreeSet<String> tSet = new TreeSet<String>(
				new Comparator<String>() {

					@Override
					public int compare(String str1, String str2) {
						return str2.compareTo(str1);
					}
				}); 

		// add LinkedHashSet to TreeSet for reverse-sorting elements
		tSet.addAll(lhsCompanies);

		// Iterating using enhanced for-loop
		System.out.println("\n\nDescending sorting-order:"
				+ " Iterating TreeSet\n");
		for(String company : tSet) {
			System.out.println(company);
		}
	}
}

Output:

Insertion Order: Iterating LinkedHashSet

LinkedIn
Amazon
Google
Apple
Facebook
Oracle
Microsoft


Descending sorting-order: Iterating TreeSet

Oracle
Microsoft
LinkedIn
Google
Facebook
Apple
Amazon

 

Way 3: Using ArrayList and Collections’ class utility method sort();

Steps:

• Create new LinkedHashSet object
• Store/add contents to LinkedHashSet
• Convert LinkedHashSet to ArrayList using inter-conversion constructor
• Invoke sort(); method on ArrayList contents using Collections‘ class
• Invoke clear(); method on original LinkedHashSet, if we want to convert back ArrayList to LinkedHashSet
• Finally, convert ArrayList to LinkedHashSet by adding ArrayList contents to LinkedHashSet, as LinkedHashSet maintains insertion-order, if we want to retain original LinkedHashSet
• Note : we can sort in reverse-order using Comparator and providing reverse-order sorting logic

Syntax:

// convert LinkedHashSet to ArrayList
List<String> lst = new ArrayList<String>(lhsCompanies);

// sort using Collections class
Collections.sort(lst);

// clear or empty LinkedHashSet
lhsCompanies.clear();

// convert sorted ArrayList to LinkedHashSet, afetr clear();
lhsCompanies.addAll(lst);

SortingLinkedHashSetUsingArrayList.java

package in.bench.resources.collection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;

public class SortingLinkedHashSetUsingArrayList {

	public static void main(String[] args) {

		// creating LinkedHashSet object of type String
		LinkedHashSet<String> lhsCompanies = 
				new LinkedHashSet<String>();

		// adding elements to LinkedHashSet object
		lhsCompanies.add("LinkedIn");
		lhsCompanies.add("Amazon");
		lhsCompanies.add("Google");
		lhsCompanies.add("Apple");
		lhsCompanies.add("Facebook");
		lhsCompanies.add("Oracle");
		lhsCompanies.add("Microsoft");

		// Iterating using enhanced for-loop
		System.out.println("Insertion Order:"
				+ " Iterating LinkedHashSet\n");
		for(String company : lhsCompanies) {
			System.out.println(company);
		}

		// convert LinkedHashSet to ArrayList
		List<String> lst = new ArrayList<String>(lhsCompanies);

		// sort using Collections class
		Collections.sort(lst);

		// clear or empty LinkedHashSet
		lhsCompanies.clear();

		// convert sorted ArrayList to LinkedHashSet, afetr clear();
		lhsCompanies.addAll(lst);

		// Iterating using enhanced for-loop
		System.out.println("\n\nAscending sorting-order:"
				+ " Iterating LinkedHashSet\n");
		for(String company : lhsCompanies) {
			System.out.println(company);
		}
	}
}

Output:

Insertion Order: Iterating LinkedHashSet

LinkedIn
Amazon
Google
Apple
Facebook
Oracle
Microsoft


Ascending sorting-order: Iterating LinkedHashSet

Amazon
Apple
Facebook
Google
LinkedIn
Microsoft
Oracle

 

References:

• https://docs.oracle.com/javase/tutorial/collections/intro/
• https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html
• https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Set.html
• https://docs.oracle.com/javase/7/docs/api/java/util/class-use/HashSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/HashSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashSet.html
• http://docs.oracle.com/javase/7/docs/api/index.html?java/util/class-use/LinkedHashSet.html

 

Happy Coding !!
Happy Learning !!