Java Comparator Example for custom sorting by employee age and department

This program illustrates , how to sort custom object using Comparator<T>. We have used Employee list to sort by age and department. As per the default ordering it will follow the natural ordering.

The below Employee class is our POJO , we will use this class to sort the employee list by age and department.

Employee.java

package com.javadevelopersguide.lab.basic;
/**
 * @author manoj.bardhan
 *
 */
public class Employee {
private String name;
private int age;
private String department;
public Employee(String name, int age, String department) {
super();
this.name = name;
this.age = age;
this.department = department;
}
@Override
public String toString() {
return "\n Employee [name=" + name + ", age=" + age + ", department=" + department + "]";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getDepartment() {
return department;
}
public void setDepartment(String department) {
this.department = department;
}
}

Now, we need to create a comparator to compare two same objects. We can create as many comparators by implementing each field/attributes of the POJO. Its purely business requirement, how you need your sorting functionality. Here we need the sorting based on the employee  age and employee department.

EmployeeAgeComparator.java

package com.javadevelopersguide.lab.basic;
import java.util.Comparator;
/**
 * EmployeeAgeComparator is a comparator by Age.
 *
 * @author manoj.bardhan
 *
 */
public class EmployeeAgeComparator implements Comparator<Employee> {
@Override
public int compare(Employee emp1, Employee emp2) {
return emp1.getAge() - emp2.getAge();
}
}

EmployeeDeptComparator.java

package com.javadevelopersguide.lab.basic;
import java.util.Comparator;
/**
 * EmployeeDeptComparator is comparator by department.
 *
 * @author manoj.bardhan
 *
 */
public class EmployeeDeptComparator implements Comparator<Employee> {
@Override
public int compare(Employee emp1, Employee emp2) {
// Internally for comparing String we need to use compareTo()
return emp1.getDepartment().compareTo(emp2.getDepartment());
}
}

In the above we created two comparator for age and department. Now, we need to action on our comparators. We will call our newly created comparator from main() and see the result. Below EmployeeComparatorExample class show the comparator in action.

EmployeeComparatorExample.java

package com.javadevelopersguide.lab.basic;
import java.util.ArrayList;
import java.util.Collections;
/**
 * This program illustrates the simple use of Comparator<t> interface.
 *
 * @author manoj.bardhan
 *
 */
public class EmployeeComparatorExample {
public static void main(String[] args) {
Employee e1 = new Employee("Matt Kuban", 32, "IT");
Employee e2 = new Employee("Andrew Smith", 42, "HR");
Employee e3 = new Employee("Butler Jason", 52, "HR");
Employee e4 = new Employee("Miss Linda", 35, "HR");
Employee e5 = new Employee("Bradley Head", 23, "IT");
Employee e6 = new Employee("Peter Parker", 34, "ADMIN");
// Create an arraylist and add all the employee object into that list.
ArrayList<Employee> employeeList = new ArrayList<Employee>();
employeeList.add(e1);
employeeList.add(e2);
employeeList.add(e3);
employeeList.add(e4);
employeeList.add(e5);
employeeList.add(e6);
System.out.println("Employee Before Sort ::" + employeeList);
// Using EmployeeAgeComparator - to sort the employee by Age
EmployeeAgeComparator ageComparator = new EmployeeAgeComparator();
Collections.sort(employeeList, ageComparator);
// Using EmployeeDeptComparator - to sort the employee by Department
EmployeeDeptComparator deptComparator = new EmployeeDeptComparator();
Collections.sort(employeeList, deptComparator);
System.out.println("Employee After Sort ::" + employeeList);
}
}

Output :- 

Employee Before Sort ::[
 Employee [name=Matt Kuban, age=32, department=IT],
 Employee [name=Andrew Smith, age=42, department=HR],
 Employee [name=Butler Jason, age=52, department=HR],
 Employee [name=Miss Linda, age=35, department=HR],
 Employee [name=Bradley Head, age=23, department=IT],
 Employee [name=Peter Parker, age=34, department=ADMIN]]

Employee After Sort ::[
 Employee [name=Peter Parker, age=34, department=ADMIN],
 Employee [name=Miss Linda, age=35, department=HR],
 Employee [name=Andrew Smith, age=42, department=HR],
 Employee [name=Butler Jason, age=52, department=HR],
 Employee [name=Bradley Head, age=23, department=IT],
 Employee [name=Matt Kuban, age=32, department=IT]]

Happy Learning.

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