Java 8 – Comparator thenComparing() example

Java example to sort list of objects by multiple fields using Comparator.thenComparing() method. This method returns a lexicographic-order comparator with another comparator. It gives the same effect as SQL group by clause.

Quick Reference:

//first name comparator
Comparator<Employee> compareByFirstName = Comparator.comparing( Employee::getFirstName );

//last name comparator
Comparator<Employee> compareByLastName = Comparator.comparing( Employee::getLastName );

//Compare by first name and then last name (multiple fields)
Comparator<Employee> compareByFullName = compareByFirstName.thenComparing(compareByLastName);

//Use Comparator
Collections.sort(employees, compareByFullName);

Sort on multiple fields – Group by sort

Example of using thenComparing() to create Comparator which is capable of sorting by multiple fields.

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class JavaSort 
{
	public static void main(String[] args) 
	{
		ArrayList<Employee> employees = getUnsortedEmployeeList();
		
		//Compare by first name and then last name
		Comparator<Employee> compareByName = Comparator
												.comparing(Employee::getFirstName)
												.thenComparing(Employee::getLastName);
		
		Collections.sort(employees, compareByName);
		
		System.out.println(employees);
	}

	private static ArrayList<Employee> getUnsortedEmployeeList() 
	{
		ArrayList<Employee> list = new ArrayList<>();
		list.add( new Employee(2, "Lokesh", "Gupta") );
		list.add( new Employee(1, "Alex", "Gussin") );
		list.add( new Employee(4, "Brian", "Sux") );
		list.add( new Employee(5, "Neon", "Piper") );
		list.add( new Employee(3, "David", "Beckham") );
		list.add( new Employee(7, "Alex", "Beckham") );
		list.add( new Employee(6, "Brian", "Suxena") );
        return list;
	}
}

//Output:

[E[id=7, firstName=Alex, 	lastName=Beckham], 
E [id=1, firstName=Alex, 	lastName=Gussin], 
E [id=4, firstName=Brian, 	lastName=Sux], 
E [id=6, firstName=Brian, 	lastName=Suxena], 
E [id=3, firstName=David, 	lastName=Beckham], 
E [id=2, firstName=Lokesh, 	lastName=Gupta], 
E [id=5, firstName=Neon, 	lastName=Piper]]

Drop me your questions in comments section.

Happy Learning !!

Reference:

Comparator.thenComparing() Java Doc