Comparator - Java 8

 Comparator interface now have multiple functions which will helps us to have multiple comparison together. see below

1. Comparator.comparing() : static method which takes comparator to compare
2. thenComparaing(): use it when you want to have another comparator to compare
3. thenComparingInt, thenComparingDouble, thenComparingLong : specialized for primitive types.

Example: 

 

In the given example we have made flexibility to sort the employee List by firstName, lastName or Salary and sorting order can be asc/desc

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
 
public class ComparatorTest
{
    public static void main(String[] args) 
    {
        ArrayList<Employee> employees = getUnsortedEmployeeList();
         
        //Compare by first name and then last name
        Comparator<Employee> compareByName = getCompareBy("salary");

        System.out.println(getSortedList(employees, "asc", compareByName));
    }

    static Comparator<Employee> getCompareBy(String field)
    {
        if(field.equalsIgnoreCase("salary"))
        {

            return Comparator.comparing((Employee e1)->e1.getSalary().getValue())
                .thenComparing(Employee::getFirstName)
                .thenComparing(Employee::getLastName);
        }
        else if (field.equalsIgnoreCase("lastName"))
        {
            return Comparator
                .comparing(Employee::getLastName)
                .thenComparing(Employee::getFirstName)
                .thenComparing((Employee e1)->e1.getSalary().getValue());
        }
        return Comparator
            .comparing(Employee::getFirstName)
            .thenComparing(Employee::getLastName)
            .thenComparing((Employee e1)->e1.getSalary().getValue());
    }

    static List<Employee> getSortedList(ArrayList<Employee> employees, String order, Comparator<Employee> compareByName)
    {
        if(order.equalsIgnoreCase("desc"))
        {
            compareByName = compareByName.reversed();
        }
        return employees.stream()
            .sorted(compareByName)
            .collect(Collectors.toList());
    }
    private static ArrayList<Employee> getUnsortedEmployeeList() 
    {
        ArrayList<Employee> list = new ArrayList<>();
        list.add( new Employee(new Salary(new BigDecimal(500000)), "Bipin", "Gupta"));
        list.add( new Employee(new Salary(new BigDecimal(800000)), "Umesh", "Mehta"));
        list.add( new Employee(new Salary(new BigDecimal(600000)), "Ramesh", "Dangi"));
        list.add( new Employee(new Salary(new BigDecimal(1000000)), "Atin", "Kapoor"));
        list.add( new Employee(new Salary(new BigDecimal(800000)), "Aman", "Verma"));
        list.add( new Employee(new Salary(new BigDecimal(550000)), "Rahi", "Akela"));
        list.add( new Employee(new Salary(new BigDecimal(500000)), "Dinesh", "Mehta"));
        return list;
    }
}

public class Employee {

  private Salary salary;
  private String firstName;
  private String lastName;

  public Employee(Salary salary, String firstName, String lastName) {
    this.salary    = salary;
    this.firstName = firstName;
    this.lastName  = lastName;
  }

  public Salary getSalary() {
    return salary;
  }

  public void setSalary(Salary salary) {
    this.salary = salary;
  }

  public String getFirstName() {
    return firstName;
  }

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

  public String getLastName() {
    return lastName;
  }

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

  @Override
  public String toString() {
    return firstName+":"+lastName+":"+ salary.getValue().toString();
  }
}

import java.math.BigDecimal;

public class Salary
{
private BigDecimal value;

  public Salary(BigDecimal i) {
    this.value = i;
  }

  public BigDecimal getValue() {
    return value;
  }

  public void setValue(BigDecimal value) {
    this.value = value;
  }
}


Output:
[Bipin:Gupta:500000, Dinesh:Mehta:500000, Rahi:Akela:550000, Ramesh:Dangi:600000, Aman:Verma:800000, Umesh:Mehta:800000, Atin:Kapoor:1000000]