In one of the previous articles, we have discussed how to sort list of objects on the basis of single field/attribute using Comparable and Comparator interfaces

Read Java 8 – Sorting list of objects on multiple fields for sorting list of Objects on the basis of multiple field using Java 8 Comparator and Stream‘s sorted() method

1. Sorting lists of Objects on Single field/parameter :

Sorting ArrayList contents in both ascending/descending order on the basis of single field

2. Sorting list of Objects on Multiple field/parameters :

What if we have a requirement to sort ArrayList of objects in accordance with 2/3 fields like,

First, sort according to customer name
Second, sort according to customer city if names are same
Third sorting w.r.t customer age if name/city are same

2.1 Steps to sort ArrayList contents w.r.t 3 member variables of Customer class :

Define Customer class with 3 member variables namely customer name, city and age
Write a custom sorting logic to sort Customer member variables w.r.t 3 field/parameters as per sequence (Name –> City –> Age)
Main test class, where we are going to create ArrayList and inserts some 10+ entries of Customer objects
Finally printing Customer objects before & after custom sorting logic from main class

Customer.java

package in.bench.resources.customized.sorting.multiple.fields;

public class Customer {

	// member variables
	String custName;
	String custCity;
	Integer custAge;

	// getters & setters

	// 3-arg parameterized constructor

	// overriding toString() method
}

CustomerSortingComparator.java

package in.bench.resources.customized.sorting.multiple.fields;

import java.util.Comparator;

public class CustomerSortingComparator implements Comparator<Customer> {

	@Override
	public int compare(Customer cust1, Customer cust2) {

		// 1. name comparison in alphabetical-order
		int compareName = cust1.getCustName().compareTo(cust2.getCustName());

		// 2. city comparison in alphabetical-order
		int compareCity = cust1.getCustCity().compareTo(cust2.getCustCity());

		// 3. age comparison in ascending-order
		int compareAge = cust1.getCustAge().compareTo(cust2.getCustAge());


		// 3-level comparison using if-else block
		if(compareName == 0) {
			return ((compareCity == 0) ? compareAge : compareCity);
		}
		else {
			return compareName;
		}
	}
}

TestCustomerSorting.java

package in.bench.resources.customized.sorting.multiple.fields;

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

public class TestCustomerSorting {

	public static void main(String[] args) {

		// 1. create ArrayList reference to store customers
		List<Customer> listOfCustomers = new ArrayList<Customer>();


		// 1.1 create customer objects using constructor initialization
		Customer cust1 = new Customer("Shalini", "Chennai", 60);
		Customer cust2 = new Customer("Sneha", "Pune",  73);
		Customer cust3 = new Customer("Simran", "Bangalore", 37);
		Customer cust4 = new Customer("Trisha", "Hyderabad", 52);
		Customer cust5 = new Customer("Shalini", "Chennai", 70);
		Customer cust6 = new Customer("Abirami", "Bangalore", 48);
		Customer cust7 = new Customer("Trisha", "Mangalore", 45);
		Customer cust8 = new Customer("Sneha", "Pune", 62);
		Customer cust9 = new Customer("Shalini", "Chennai",  50);


		// 1.2 add customer objects to ArrayList
		listOfCustomers.add(cust1);
		listOfCustomers.add(cust2);
		listOfCustomers.add(cust3);
		listOfCustomers.add(cust4);
		listOfCustomers.add(cust5);
		listOfCustomers.add(cust6);
		listOfCustomers.add(cust7);
		listOfCustomers.add(cust8);
		listOfCustomers.add(cust9);


		// 1.4 before Sorting: iterate using Iterator and while-loop
		Iterator<Customer> custIterator =
				listOfCustomers.iterator();


		// 1.5 print to console
		System.out.println("Before Sorting - Insertion-order of List :-\n");
		while(custIterator.hasNext()) {
			System.out.println(custIterator.next());
		}



		// 2. sorting using Collections.sort()
		Collections.sort(listOfCustomers, new CustomerSortingComparator());


		// 2.1 after Sorting: iterate using enhanced for-loop
		System.out.println("\n\nSorted order of Name -> City -> Age :-\n");
		for(Customer customer : listOfCustomers) {
			System.out.println(customer);
		}
	}
}

Output:

Before Sorting - Insertion-order of List :-

Customer [custName=Shalini, custCity=Chennai, custAge=60]
Customer [custName=Sneha, custCity=Pune, custAge=73]
Customer [custName=Simran, custCity=Bangalore, custAge=37]
Customer [custName=Trisha, custCity=Hyderabad, custAge=52]
Customer [custName=Shalini, custCity=Chennai, custAge=70]
Customer [custName=Abirami, custCity=Bangalore, custAge=48]
Customer [custName=Trisha, custCity=Mangalore, custAge=45]
Customer [custName=Sneha, custCity=Pune, custAge=62]
Customer [custName=Shalini, custCity=Chennai, custAge=50]


Sorted order of Name -> City -> Age :-

Customer [custName=Abirami, custCity=Bangalore, custAge=48]
Customer [custName=Shalini, custCity=Chennai, custAge=50]
Customer [custName=Shalini, custCity=Chennai, custAge=60]
Customer [custName=Shalini, custCity=Chennai, custAge=70]
Customer [custName=Simran, custCity=Bangalore, custAge=37]
Customer [custName=Sneha, custCity=Pune, custAge=62]
Customer [custName=Sneha, custCity=Pune, custAge=73]
Customer [custName=Trisha, custCity=Hyderabad, custAge=52]
Customer [custName=Trisha, custCity=Mangalore, custAge=45]

References :

Happy Coding !!
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