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What is compareTo() method in Java ?

compareTo() method is defined in interface java.lang.Comparable and it is used to implement natural sorting on java classes. natural sorting means the the sort order which naturally applies on object e.g. lexical order for String, numeric order for Integer or Sorting employee by there ID etc. most of the java core classes including String and Integer implements CompareTo() method and provide natural sorting.

Sorting ArrayList in Java with natural Order

In Order to Sort Java ArrayList on natural order of elements, object stored in ArrayList must implement Comparable interface in Java and should override compareTo() method as per there natural order.


package test;


import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;


public class ArrayListSortingExample {


   private static class SmartPhone implements Comparable

        private String brand;

        private String model;

        private int price;


        public SmartPhone(String brand, String model, int price){

            this.brand = brand;

            this.model = model;

            this.price = price;




        public int compareTo(SmartPhone sp) {

            return this.brand.compareTo(sp.brand);




        public String toString() {

            return "SmartPhone{" + "brand=" + brand + ", model=" + model + ", price=" + price + '}';





    private static class PriceComparator implements Comparator



        public int compare(SmartPhone sp1, SmartPhone sp2) {

            return (sp1.price < sp2.price ) ? -1: (sp1.price > sp2.price) ? 1:0 ;





    public static void main(String... args) {


        //creating objects for arraylist sorting example

        SmartPhone apple = new SmartPhone("Apple", "IPhone4S",1000);

        SmartPhone nokia = new SmartPhone("Nokia", "Lumia 800",600);

        SmartPhone samsung = new SmartPhone("Samsung", "Galaxy Ace",800);

        SmartPhone lg = new SmartPhone("LG", "Optimus",500);


        //creating Arraylist for sorting example



        //storing objects into ArrayList for sorting






        //Sorting Arraylist in Java on natural order of object



        //print sorted arraylist on natural order



        //Sorting Arraylist in Java on custom order defined by Comparator

        Collections.sort(smartPhones,new PriceComparator());


        //print sorted arraylist on custom order





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