Comparable and Comparator interfaces-Part 2

We have already seen the Comparable interface at work now let us see how to create comparators.

We will use the same Employee class.But without any Comparable interface implmentation. Now we have EmployeePojo class listed below:

package blog.javaespresso.comparable.example.bean;

import java.util.Date;

public class EmployeePojo {
 public EmployeePojo(){}
 public EmployeePojo(int empId,String name,double salary,Date dateOfJoining){
  this.empId = empId;this.name =  name;
  this.salary =  salary;this.dateOfJoining = dateOfJoining;
 }
 private int empId;
 private String name;
 private double salary;
 private Date dateOfJoining;

 // setters and getters
 public int getEmpId() {return empId;}
 public void setEmpId(int empId) {this.empId = empId;}
 public String getName() {return name;}
 public void setName(String name) {this.name = name;}
 public double getSalary() {return salary;}
 public void setSalary(double salary) {this.salary = salary;}
 public Date getDateOfJoining() {return dateOfJoining;}
 public void setDateOfJoining(Date dateOfJoining) {this.dateOfJoining = dateOfJoining;}
}

So objective is we need to display a report and report has options of sorting the employees either by name or date of joining.
take a look at the code listings:
Employee Name Comparator Class

package package blog.javaespresso.comparator.example.customcomparator;

import java.util.Comparator;
import blog.javaespresso.comparable.example.bean.EmployeePojo;

public class EmployeeNameComparator implements Comparator<EmployeePojo>{

 @Override
 public int compare(EmployeePojo e1, EmployeePojo e2) {
  if(e1 == null || e2 == null){
   throw new NullPointerException("compareTo: Argument passed is null");
  }
   return e1.getName().compareTo(e2.getName());
 }

}

Employee Date Of Joining Comparator Class

package package blog.javaespresso.comparator.example.customcomparator;

import java.util.Comparator;
import blog.javaespresso.comparable.example.bean.EmployeePojo;

public class EmployeeDOJComparator implements Comparator<EmployeePojo>{

 @Override
 public int compare(EmployeePojo e1, EmployeePojo e2) {
  if(e1 == null || e2 == null){
   throw new NullPointerException("compareTo: Argument passed is null");
  }
   return new Integer(e1.getDateOfJoining().compareTo(e2.getDateOfJoining()));
 }

}

Employee Comparator sorting test class:
We first create some employee objects and then first we sort them using name comparator and then using DOJ comparator

package blog.javaespresso.comparator.example.test;

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

import blog.javaespresso.comparable.example.bean.EmployeePojo;
import blog.javaespresso.comparator.example.customcomparator.EmployeeDOJComparator;
import blog.javaespresso.comparator.example.customcomparator.EmployeeNameComparator;

public class TestEmployeeComparatorSorting {
 public static void main(String[] args) {
  EmployeePojo e1 = new EmployeePojo(1,"A",20000.00,new Date(2010,12,11));
  EmployeePojo e2 = new EmployeePojo(2,"A",22000.00,new Date(2009,12,11));
  EmployeePojo e3 = new EmployeePojo(3,"A",10000.00,new Date(1990,12,11));
  EmployeePojo e4 = new EmployeePojo(4,"F",19000.00,new Date(2001,12,11));
  EmployeePojo e5 = new EmployeePojo(5,"E",24000.00,new Date(2006,12,11));
  List<EmployeePojo> list = new ArrayList<EmployeePojo>();
  list.add(e1);list.add(e2);list.add(e3);list.add(e4);list.add(e5);

  Collections.sort(list,new EmployeeNameComparator());
  // PRINT AFTER SORTED BY NAME
  System.out.println("AFTER SORTED BY NAME");
  System.out.println("===============================================================");
  System.out.println("ID  Name  Salary  Date Of Joining");
  System.out.println("===============================================================");
  for (EmployeePojo employee : list) {
   System.out.println(employee.getEmpId()+"\t\t "+employee.getName()
     +"\t\t"+employee.getSalary()+"\t\t "+
     employee.getDateOfJoining().getDay()+"-"+employee.getDateOfJoining().getMonth()
     +"-"+employee.getDateOfJoining().getYear());
  }

  // sorting the EmployeePojo object

  Collections.sort(list,new EmployeeDOJComparator());

  // PRINT AFTER SORTED BY AGE
  System.out.println("AFTER SORTED BY DATE OF JOINING");
  System.out.println("===============================================================");
  System.out.println("ID  Name  Salary  Date Of Joining");
  System.out.println("===============================================================");
  for (EmployeePojo employee : list) {
   System.out.println(employee.getEmpId()+"\t\t "+employee.getName()
     +"\t\t"+employee.getSalary()+"\t\t "+
     employee.getDateOfJoining().getDay()+"-"+employee.getDateOfJoining().getMonth()
     +"-"+employee.getDateOfJoining().getYear());
  }
 }
}

Comparable and Comparator interfaces-Part 1
Part-3:Sorting objects with more than one attribute