Comparable and Comparator in Java

Employee record with Department, Emp Name and Emp Id:

Original Data:

BI :Kondal :109

HANA :Ban :103

HANA :Anand :115

ERP :Can :102

CRM :Yangi :100

BI :Damn :114

Required Format: Display the emp names in sorted way based on the department name.

BI :Damn :114

BI :Kondal :109

CRM :Yangi :100

ERP :Can :102

HANA :Anand :115

HANA :Ban :103

We can acheive this in two different ways.

1.  By implementing comparable interface in Employee class.

 - Override compareTo method

 - Invoke Collections.sort(arraylist);

2. By implementing comparator interface, as specified below without even touching the employee class

- Override compare method

- Invoke Collections.sort(arraylist, new EmployeeComparator());

Employee class

public

class Employee /* implements Comparable<Employee>*/ {

private int empId;

private String empName;

private String department;

public Employee(int empId, String empName, String department) {

this.empId = empId;

this.empName = empName;

this.department = department;

}

public void setEmpId(int empId) {

this.empId = empId;

}

public void setEmpName(String empName) {

this.empName = empName;

}

public int getEmpId() {

return empId;

}

public String getEmpName() {

return empName;

}

public String getDepartment() {

return department;

}

public void setDepartment(String department) {

this.department = department;

}

/* @Override

public int compareTo(Employee o) {

if (this.getDepartment().compareTo(o.getDepartment()) == 0) {

return this.getEmpName().compareTo(o.getEmpName());

}

return this.getDepartment().compareTo(o.getDepartment());

}*/

}

 

EmployeeComparator class

import

java.util.Comparator;

　

public

class EmployeeComparator implements Comparator<Employee>{

@Override

public

int compare(Employee e1, Employee e2) {

if

(e1.getDepartment().compareTo(e2.getDepartment()) == 0) {

return

e1.getEmpName().compareTo(e2.getEmpName());

}

return

e1.getDepartment().compareTo(e2.getDepartment());

}

}

EmployeProfiles class

import

java.util.ArrayList;

import

java.util.Collections;

public

class EmployeProfiles {

public

static void main(String[] args) {

ArrayList<Employee> empList = new

ArrayList<Employee>();

empList.add(new

Employee(109, "Kondal", "BI"));

empList.add(new

Employee(103, "Ban", "HANA"));

empList.add(new

Employee(115, "Anand", "HANA"));

empList.add(new

Employee(102, "Can", "ERP"));

empList.add(new

Employee(100, "Yangi", "CRM"));

empList.add(new

Employee(114, "Damn", "BI"));

// Natural order in the array list

for

(Employee employee : empList) {

System.out

.println(employee.getDepartment() + " :"

+ employee.getEmpName() + " :" + employee.getEmpId());

}

// Apply sorting

Collections.sort(empList, new

EmployeeComparator());

System.out

.println("------------");

// sorted list

for

(Employee employee : empList) {

System.out

.println(employee.getDepartment() + " :"

+ employee.getEmpName() + " :" + employee.getEmpId());

}

}

}