Sorting an List of Objects

Elements in an ArrayList can be sorted using the Collections.sort() method.
If we want to sort Objects in an ArraList based on any particular field(s) then we need to implement the Comparator interface and override the compare method.
For Example :

I have a class called Employee.

public class Employee {

 private String empName;
 private int empId;
 public String empLocation;
 
 /**
  * @return the empName
  */
 public String getEmpName() {
  return empName;
 }

 /**
  * @param empName the empName to set
  */
 public void setEmpName(String empName) {
  this.empName = empName;
 }

 /**
  * @return the empId
  */
 public int getEmpId() {
  return empId;
 }

 /**
  * @param empId the empId to set
  */
 public void setEmpId(int empId) {
  this.empId = empId;
 }

 /**
  * @return the empLocation
  */
 public String getEmpLocation() {
  return empLocation;
 }

 /**
  * @param empLocation the empLocation to set
  */
 public void setEmpLocation(String empLocation) {
  this.empLocation = empLocation;
 }

}

Sorting :

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

/**
*
*/

/**
* @author ADMIN
*
*/
public class Main {

 /**
  * @param args
  */
 public static void main(String[] args) {
  Employee e1 = new Employee("Baskar",1,"Chennai");
  Employee e2 = new Employee("Vinay",2,"Chennai");
  Employee e3 = new Employee("Mani",3,"Chennai");
  Employee e4 = new Employee("Raj",4,"Chennai");

  List employeeList = new ArrayList();
  employeeList.add(e1);
  employeeList.add(e2);
  employeeList.add(e3);
  employeeList.add(e4);
  System.out.println("List before sorting "+employeeList.toString());
  Collections.sort(employeeList, new Comparator(){
   
           public int compare(Object o1, Object o2) {
               Employee e1 = (Employee) o1;
               Employee e2 = (Employee) o2;
              return e1.getEmpName().compareToIgnoreCase(e2.getEmpName());
           }

       });
  
  System.out.println("List after sorting "+employeeList.toString());
 }

}


Result :

List before sorting [Baskar -- 1 -- Chennai, Vinay -- 2 -- Chennai, Mani -- 3 -- Chennai, Raj -- 4 -- Chennai]
List after sorting [Baskar -- 1 -- Chennai, Mani -- 3 -- Chennai, Raj -- 4 -- Chennai, Vinay -- 2 -- Chennai]