How to compare objects by multiple fields

Question

Assume you have some objects which have several fields they can be compared by:

public class Person {

    private String firstName;
    private String lastN         


        

Answer 1

Code implementation of the same is here if we have to sort the Person object based on multiple fields.

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

public class Person {

private String firstName;
private String lastName;
private int age;

public String getFirstName() {
    return firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

public String getLastName() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

public Person(String firstName, String lastName, int age) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
}


static class PersonSortingComparator implements Comparator {

    @Override
    public int compare(Person person1, Person person2) {

        // for first name comparison
        int firstNameCompare = person1.getFirstName().compareTo(person2.getFirstName());

        // for last name comparison
        int lastNameCompare = person1.getLastName().compareTo(person2.getLastName());

        // for last name comparison
        int ageCompare = person1.getAge() - person2.getAge();

        // Now comparing
        if (firstNameCompare == 0) {
            if (lastNameCompare == 0) {
                return ageCompare;
            }
            return lastNameCompare;
        }
        return firstNameCompare;
    }
}

public static void main(String[] args) {
    Person person1 = new Person("Ajay", "Kumar", 27);
    Person person2 = new Person("Ajay","Gupta", 23);
    Person person3 = new Person("Ajay","Kumar", 22);


    ArrayList persons = new ArrayList<>();
    persons.add(person1);
    persons.add(person2);
    persons.add(person3);


    System.out.println("Before Sorting:\n");
    for (Person person : persons) {
        System.out.println(person.firstName + " " + person.lastName + " " + person.age);
    }

    Collections.sort(persons, new PersonSortingComparator());

    System.out.println("After Sorting:\n");
    for (Person person : persons) {
        System.out.println(person.firstName + " " + person.lastName + " " + person.age);
    }
}

}