Sorting of List of Objects based on Custom parameter Java

Question

I am writing a component where it requires to sort upon Object variable parameter. For example: Employee has variable lastName. I want to sort the employees by the lastName.lenght() I have seen many examples,but i could not find an answer Can I achieve the result in this way or do we need a different approach.

I am giving the example

public class Employee {
    private int Id;
    private String firstName;
    private String lastName;
    private String department;

    public Employee(int id, String firstName, String lastName, String department) {
        Id = id;
        this.firstName = firstName;
        this.lastName = lastName;
        this.department = department;
    }

    public Employee() {
    }

    public int getId() {
        return Id;
    }

    public void setId(int id) {
        Id = id;
    }

    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 String getDepartment() {
        return department;
    }

    public void setDepartment(String department) {
        this.department = department;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "Id=" + Id +
                ", firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", department='" + department + '\'' +
                '}';
    }
}

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class SortExample
{
    public static void main(String[] args)
    {
        ArrayList<Employee> employees = getUnsortedEmployeeList();
        Comparator<Employee> compareByName = Comparator
                .comparing(Employee::getFirstName).reversed();

        Comparator<Employee> compareByLastName = Comparator
                .comparing(Employee::getLastName).reversed();


        
        List<Employee> sortedEmployees = employees.stream()
                .sorted(compareByName)
                .sorted(compareByLastName)
        //I have commented the code
        //.sorted((e1,e2) ->e1.getLastName().length().compareTo(e2.getLastName().length()))
                .collect(Collectors.toList());

        System.out.println(sortedEmployees);
    }

    private static ArrayList<Employee> getUnsortedEmployeeList()
    {
        ArrayList<Employee> list = new ArrayList<>();
        list.add( new Employee(2, "Irene", "Parr","programming") );
        list.add( new Employee(1, "Nicola", "Mitchell","programming") );
        list.add( new Employee(4, "Emily", "Carr","finance") );
        list.add( new Employee(5, "Blake", "Baker","finance") );
        list.add( new Employee(3, "Natalie", "Parsons","marketing") );
        list.add( new Employee(7, "Olivia", "Clarkson","marketing") );
        list.add( new Employee(6, "Justin", "Scott","marketing") );

        return list;
    }
}

Any help would be appreciated.

Answer 1

You might want to get familiar with Java 8 static methods of the Comparator interface like comparing() , comparingInt() , etc.

List<Employee> sortedEmployees = employees.stream()
    .sorted(Comparator.comparingInt(employee -> employee.getLastName().length()))
    .collect(Collectors.toList());

Also, don't sort the data multiple times (ie avoid applying sorted() more than once), instead you can chain the comparators by using different flavors of the method thenComparing() .