How to implement a java.lang.Comparable

Java.lang.Comparable is an interface used for sorting collections. The classes implementing Comparables must implement the compareTo() method. Here is a simple example of how a comparable can be used. The example sorts a list of employees on the basis of their age. In this example we have a simple pojo named Employee.java implementing a java.lang.Comparable interface by overriding the compareTo method and a main class to demonstrate the functionality.

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 o) {

            if(this.age>((Employee)o).getAge()){

                        return 1;

            } else if(this.age<((Employee)o).getAge()){

                        return -1;

            } else{

                        return 0;

            }

}

}

ComparableExample:

package com.soft.examples;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import com.soft.model.Employee;

public class ComparableExample {

            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);

                        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("************ 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());

                        }

                       

            }

}

This functionality can also be achieved with a java.util.Comparator, the implementation of which is given at

 How to implement a comparator

The differences between java.util.Comparator and java.lang.Comparable interfaces are given at

 Differences between Comparator and Comparable