How to implement ReverseOrderComparator

Java.Util.Comparator is an interface used for sorting collections. In previous example, we used a MultyField Comparator to sort a list in ascending order by multiple fields. In this example, we will implement a reverse order multy field Comparator in order to achieve a sorting in descending order or in other words in reverse order of whatever is implemented in the Comparator. This can be achieved just by a single line of code as

Comparator c= Collections.reverseOrder(new mployeeMultyFieldComparator());

 This example is almost a replica of the previous example. It consists of the following 3 classes.

Employee.java:

package com.soft.model;

public class Employee{

private String name;

private String department;

private int age;

public String getName() {

            return name;

}

public void setName(String name) {

            this.name = name;

}

public String getDepartment() {

            return department;

}

public void setDepartment(String department) {

            this.department = department;

}

public int getAge() {

            return age;

}

public void setAge(int age) {

            this.age = age;

}

}

EmployeeMultyFieldComparator.java:

package com.soft.model;

import java.util.Comparator;

public class EmployeeMultyFieldComparator implements Comparator

            @Override

            public int compare(Object obj1, Object obj2) {

                        Employee e1=(Employee)obj1;

                        Employee e2=(Employee)obj2;

                        if(e1.getName().compareTo(e2.getName())==0){

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

                                                return e1.getAge()-e2.getAge();

                                    }else{

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

                                    }

                        }else{

                                    return e1.getName().compareTo(e2.getName());

                        }

            }

}

MultyFieldComparatorExample.java:

package com.soft.examples;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import com.soft.model.Employee;

import com.soft.model.EmployeeMultyFieldComparator;

public class MultyFieldComparatorExample {

            public static void main(String[] args) {

                        List<Employee> list= new ArrayList<Employee>();

                        Employee e=new Employee();

                        e.setName("Danial Fritz");

                        e.setDepartment("Field Based Development");

                        e.setAge(36);

                        list.add(e);

                        e=new Employee();

                        e.setName("Denis Khoo");

                        e.setDepartment("Project Management");

                        e.setAge(30);

                        list.add(e);

                        e=new Employee();

                        e.setName("Joe Kum");

                        e.setDepartment("Adminstration");

                        e.setAge(40);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(26);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(26);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(25);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Project Management");

                        e.setAge(26);

                        list.add(e);

                        System.out.println("************ Before Sorting ***********");

                        for (int i=0;i< list.size();i++){

                                    System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

                        }

                        System.out.println("************ Name, Department, Age Sorting through Comparator ***********");

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

                        for (int i=0;i< list.size();i++){

                                    System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

                        }

System.out.println("** Name, Department, Age Sorting through Comparator In Descending Order**");

Collections.sort(list,Collections.reverseOrder(new EmployeeMultyFieldComparator()));

for (int i=0;i< list.size();i++){

System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

}

                       

            }

}

Output:

************ Before Sorting ***********

Danial Fritz   ----- Field Based Development   ----- 36

Denis Khoo     ----- Project Management        ----- 30

Joe Kum        ----- Adminstration             ----- 40

Anil Kumar     ----- Information Technology    ----- 26

Anil Kumar     ----- Information Technology    ----- 26

Anil Kumar     ----- Information Technology    ----- 25

Anil Kumar-----Project Management-----26

****** Name, Department, Age Sorting through Comparator *******

Anil Kumar     ----- Information Technology     ----- 25

Anil Kumar     ----- Information Technology     ----- 26

Anil Kumar     ----- Information Technology     ----- 26

Anil Kumar     ----- Project Management         ----- 26

Danial Fritz   ----- Field Based Development    ----- 36

Denis Khoo     ----- Project Management         ----- 30

Joe Kum        ----- Adminstration              ----- 40

** Name, Department, Age Sorting through Comparator in Descending Order**

Joe Kum        ----- Adminstration                     ----- 40

Denis Khoo   ----- Project Management           ----- 30

Danial Fritz   ----- Field Based Development   ----- 36

Anil Kumar   ----- Project Management           ----- 26

Anil Kumar   ----- Information Technology     ----- 26

Anil Kumar   ----- Information Technology     ----- 26

Anil Kumar   ----- Information Technology     ----- 25

An example of a simple MultyFieldComparator can be found at

How to implement MultyFieldComparator

You may also find the following articles helpful.

How to implement ReverseOrderComparable

How to implement MultyFieldComparable

How to implement a java.lang.Comparable

How to implement a java.UtilComparator

Differences between Comparator and Comparable  

How to implement MultyFieldComparable

Java.Util.Comparable is an interface used for sorting collections. In previous example, we used Comparable for sorting by only one field. In this example, we will see a more complex Comparable which can be used to sort a list of employees based on the name, then on department and then on age. The example consists of the following 2 classes.

Employee.java:

package com.soft.model;

public class Employee implements Comparable

private String name;

private String department;

private int age;

public String getName() {

            return name;

}

public void setName(String name) {

            this.name = name;

}

public String getDepartment() {

            return department;

}

public void setDepartment(String department) {

            this.department = department;

}

public int getAge() {

            return age;

}

public void setAge(int age) {

            this.age = age;

}

@Override

public int compareTo(Object obj) {

            Employee employee=(Employee)obj;

            if(this.getName().compareTo(employee.getName())==0){

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

                                    return this.getAge()-employee.getAge();

                        }else{

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

                        }

            }else{

                        return this.getName().compareTo(employee.getName());

            }

}

}

MultyFieldComparableExample.java:

package com.soft.examples;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import com.soft.model.Employee;

public class MultyFieldComparableExample {

            public static void main(String[] args) {

                        List<Employee> list= new ArrayList<Employee>();

                        Employee e=new Employee();

                        e.setName("Danial Fritz");

                        e.setDepartment("Field Based Development");

                        e.setAge(36);

                        list.add(e);

                        e=new Employee();

                        e.setName("Denis Khoo");

                        e.setDepartment("Project Management");

                        e.setAge(30);

                        list.add(e);

                        e=new Employee();

                        e.setName("Joe Kum");

                        e.setDepartment("Adminstration");

                        e.setAge(40);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(26);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(26);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(25);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Project Management");

                        e.setAge(26);

                        list.add(e);

                        System.out.println("************ Before Sorting ***********");

                        for (int i=0;i< list.size();i++){

                                    System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

                        }

                        System.out.println("************ Name, Department, Age Sorting through Comparable ***********");

                        Collections.sort(list);

                        for (int i=0;i< list.size();i++){

                                    System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

                        }

                       

            }

}

Output:

************ Before Sorting ***********

Danial Fritz   ----- Field Based Development   ----- 36

Denis Khoo     ----- Project Management        ----- 30

Joe Kum        ----- Adminstration             ----- 40

Anil Kumar     ----- Information Technology    ----- 26

Anil Kumar     ----- Information Technology    ----- 26

Anil Kumar     ----- Information Technology    ----- 25

Anil Kumar-----Project Management-----26

****** Name, Department, Age Sorting through Comparable *******

Anil Kumar     ----- Information Technology     ----- 25

Anil Kumar     ----- Information Technology     ----- 26

Anil Kumar     ----- Information Technology     ----- 26

Anil Kumar     ----- Project Management         ----- 26

Danial Fritz   ----- Field Based Development    ----- 36

Denis Khoo     ----- Project Management         ----- 30

Joe Kum        ----- Adminstration              ----- 40

An example of a MultyFieldComparator can be found at

How to implement MultyFieldComparator 

An example of a simple Comparable can be found at

How to implement a java.lang.Comparable 

You may also find the following articles helpful.

How to implement a comparator

Differences between Comparator and Comparable  

_________________________________________________________________________

How to implement MultyFieldComparator

Java.Util.Comparator is an interface used for sorting collections. In previous example, we used comparator for sorting by only one field. In this example, we will see a more complex comparator which can be used to sort a list of employees based on the name, then on department and then on age. The example consists of the following 3 classes.

Employee.java:

package com.soft.model;

public class Employee{

private String name;

private String department;

private int age;

public String getName() {

            return name;

}

public void setName(String name) {

            this.name = name;

}

public String getDepartment() {

            return department;

}

public void setDepartment(String department) {

            this.department = department;

}

public int getAge() {

            return age;

}

public void setAge(int age) {

            this.age = age;

}

}

EmployeeMultyFieldComparator.java:

package com.soft.model;

import java.util.Comparator;

public class EmployeeMultyFieldComparator implements Comparator

            @Override

            public int compare(Object obj1, Object obj2) {

                        Employee e1=(Employee)obj1;

                        Employee e2=(Employee)obj2;

                        if(e1.getName().compareTo(e2.getName())==0){

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

                                                return e1.getAge()-e2.getAge();

                                    }else{

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

                                    }

                        }else{

                                    return e1.getName().compareTo(e2.getName());

                        }

            }

}

MultyFieldComparatorExample.java:

package com.soft.examples;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import com.soft.model.Employee;

import com.soft.model.EmployeeMultyFieldComparator;

public class MultyFieldComparatorExample {

            public static void main(String[] args) {

                        List<Employee> list= new ArrayList<Employee>();

                        Employee e=new Employee();

                        e.setName("Danial Fritz");

                        e.setDepartment("Field Based Development");

                        e.setAge(36);

                        list.add(e);

                        e=new Employee();

                        e.setName("Denis Khoo");

                        e.setDepartment("Project Management");

                        e.setAge(30);

                        list.add(e);

                        e=new Employee();

                        e.setName("Joe Kum");

                        e.setDepartment("Adminstration");

                        e.setAge(40);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(26);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(26);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Information Technology");

                        e.setAge(25);

                        list.add(e);

                        e=new Employee();

                        e.setName("Anil Kumar");

                        e.setDepartment("Project Management");

                        e.setAge(26);

                        list.add(e);

                        System.out.println("************ Before Sorting ***********");

                        for (int i=0;i< list.size();i++){

                                    System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

                        }

                        System.out.println("************ Name, Department, Age Sorting through Comparator ***********");

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

                        for (int i=0;i< list.size();i++){

                                    System.out.println(list.get(i).getName()+"-----"+list.get(i).getDepartment()+"-----"+list.get(i).getAge());

                        }

                       

            }

}

Output:

************ Before Sorting ***********

Danial Fritz   ----- Field Based Development   ----- 36

Denis Khoo     ----- Project Management        ----- 30

Joe Kum        ----- Adminstration             ----- 40

Anil Kumar     ----- Information Technology    ----- 26

Anil Kumar     ----- Information Technology    ----- 26

Anil Kumar     ----- Information Technology    ----- 25

Anil Kumar-----Project Management-----26

****** Name, Department, Age Sorting through Comparator *******

Anil Kumar     ----- Information Technology     ----- 25

Anil Kumar     ----- Information Technology     ----- 26

Anil Kumar     ----- Information Technology     ----- 26

Anil Kumar     ----- Project Management         ----- 26

Danial Fritz   ----- Field Based Development    ----- 36

Denis Khoo     ----- Project Management         ----- 30

Joe Kum        ----- Adminstration              ----- 40

An example of a simple Comparator can be found at

 How to implement a comparator

You may also find the following articles helpful.

 How to implement a java.lang.Comparable

 Differences between Comparator and Comparable